Partial revision of northern European Prionospio Malmgren, 1867 (Annelida: Spionidae)

1 European Journal of Taxonomy 1027: 1–58 https://doi.org/10.5852/ejt.2025.1027.3127 europeanjournaloftaxonomy.eu ISSN 2118-9773 2025 · Hektoen M.M. et al. This work is licensed under a Creative Commons Attribution License (CC BY 4.0) Received: 16 February 2025 • Accepted: 26 August 2025 • Published: 3 December Topic editor: Magalie Castelin • Section editor: Nataliya Budaeva • Desk editor: Eva-Maria Levermann Monograph urn:lsid:zoobank.org:pub:E566239D-16A5-4DCA-A21E-BE607419ADC7 Partial revision of northern European Prionospio Malmgren, 1867 (Annelida: Spionidae) Martin M. HEKTOEN 1,* , Vasily I. RADASHEVSKY 2,* & Torkild BAKKEN 3 1 Lab Trondheim, Åkerblå a DNV Company, Sluppenvegen 6, 7037 Trondheim, Norway. 2 A.V. Zhirmunsky National Scientific Center of Marine Biology, Far Eastern Branch of the Russian Academy of Sciences, 17 Palchevsky Street, Vladivostok 690041, Russia. 1,3 Department of Natural History, NTNU University Museum, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway. * Corresponding authors: [email protected]; [email protected] 3 Email: [email protected] Abstract. This study continues our revision of Prionospio Malmgren, 1867 from the Northeast Atlantic aiming to describe the morphology of the worms that we have previously examined using molecular methods. Nine species of Prionospio are described or redescribed and illustrated, including two new species, P.fiordicasp. nov. and P. sigvaldadottirae sp. nov. A neotype is designated for P. plumosa M. Sars, and P. tripinnata Maciolek, 1985 is considered a junior synonym of this species. We found no evidence to support the presence of P. steenstrupi Malmgren, 1867 in coastal or shelf waters of mainland Europe. Prionospio sp. 6 is distinguished but not formally described due to poor material available. An identification key for Prionospio from northern Europe is presented. Several species of Prionospio in this study demonstrate a broad geographic and bathymetric range. Keywords. Polychaeta, taxonomy, Prionospio, Norway, Europe. Hektoen M.M., Radashevsky V.I. & Bakken T. 2025. Partial revision of northern European Prionospio Malmgren, 1867 (Annelida: Spionidae). European Journal of Taxonomy 1027: 1–58. https://doi.org/10.5852/ejt.2025.1027.3127 Introduction Spionidae Grube, 1850 is one of the most specious polychaete families, currently comprising more than 600 species (Read & Fauchald 2025). Prionospio Malmgren, 1867 is the most species-rich genus of the family with more than 100 species (Blake et al. 2020). Prionospio worms are common globally from the intertidal to the deep sea and often form populations of high density. Some species are vital bioindicators in European waters (Borja et al. 2000; Borgersen et al. 2019), and thus of special interest to study. The genus Prionospio was established to accommodate P. steenstrupi Malmgren, 1867 from northern Iceland. After Malmgren (1867), Prionospio from European waters were studied and described by many European Journal of Taxonomy 1027: 1–58 (2025) 2 authors (see reviews by Mackie 1984; Maciolek 1985; Sigvaldadóttir & Mackie 1993; Sigvaldadóttir 1998). Recent reviews and revisions recognize 17 species of Prionospio from the Northeast Atlantic (from the Barents Sea south to the Strait of Gibraltar). These include P. aluta Maciolek, 1985, P. banyulensis Laubier, 1966, P. caspersi Laubier, 1962, P. cirrifera Wirén, 1883, P. cristaventralis Delgado-Blas, Díaz-Díaz & Viéitez, 2018, P. dubia Day, 1961, P. ehlersi Fauvel, 1928, P. fallax Söderström, 1920, P. malmgreni Claparède, 1868, P. multibranchiata Berkeley 1927, P. multisetosa Delgado-Blas & Peraza, 2024 P. parapari Delgado-Blas, Díaz-Díaz & Viéitez, 2018, P. plumosa M. Sars in G.O. Sars, 1872, P. pulchra Imajima, 1990, P. rikardoi Martinez & Adarraga, 2019, P. sanmartini Delgado-Blas, Díaz-Díaz & Viéitez, 2019, and P. steenstrupi. It is, however, unlikely that either P. dubia or P. multibranchiata occur in the region based on recent studies (Delgado-Blas et al. 2019; DelgadoBlas & Peraza 2024; Hektoen et al. 2024). Thus, in northern Europe (Barents, Norwegian and North seas, and the British Channel), seven species are currently thought to occur: P. banyulensis, P. cirrifera, P. fallax, P. multisetosa, P. plumosa, P. sanmartini, and P. steenstrupi. Fig. 1. Phylogram modified from Hektoen et al. (2024) based on all mitochondrial genes. The species considered in this study are marked in blue. In addition to the species marked in blue, Prionospio cirrifera Wiren, 1883 and Prionospio sp. 1 also occur in northern European waters but are not treated in this study. Species names are given in correspondence with results in this study: Prionospio multisetosa DelgadoBlas & Peraza, 2024 is Prionospio cf. dubia in Hektoen et al. (2024); Prionospiofiordicasp. nov. is Prionospio sp. 3; Prionospio sanmartini Delgado-Blas, Díaz-Díaz & Viéitez, 2019 is Prionospio cf. sanmartini; Prionospio sigvaldadottirae sp. nov. is Prionospio sp. 7. HEKTOEN M.M. et al., Partial revision of Northern European Prionospio (Annelida: Spionidae) 3 Molecular data of Prionospio are scarce, and phylogenetic relationships have been studied mainly on Asian species (Abe & Sato-Okoshi 2021; Lee et al. 2023) or species from the deep sea (Guggolz et al. 2020; Neal et al. 2022). In northern Europe, short fragments of COI were obtained by Aylagas et al. (2016) for two individuals of P. dubia and four individuals of P. ehlersi from the Bay of Biscay, Spain. The first comprehensive molecular analysis of Northeast Atlantic Prionospio was performed by Hektoen et al. (2024). Ten species from the region were studied and four of them were suggested as new to science (Prionospio sp. 1, Prionospio sp. 3, Prionospio sp. 6, and Prionospio sp. 7.; Fig. 1). It was shown that worms earlier morphologically assigned to P. multibranchiata belong to two different species and P. multibranchiata is absent in East Atlantic waters. Prionospio banyulensis was found nested within Prionospio (where it was originally assigned) and therefore transferred from Aurospio Maciolek, 1981 where it was placed by some authors (e.g., Sigvaldadóttir 1998, 2002). The purpose of the present study is to continue our revision of Prionospio from northern Europe and describe the morphology of the worms that we have previously examined using molecular methods. Prionospio cirrifera is not treated in this paper but will be discussed in an upcoming study. Material and methods New material was obtained from biomonitoring surveys conducted by Åkerblå AS, STIM AS, and the Norwegian Institute of Water Research (NIVA) along the Norwegian coast. The samples were collected and treated in accordance with the International Standard ISO:16665; collected with a 0.1 m2 Van Veen grab and washed on a 1 mm mesh sieve. The residues were fixed in 4% formaldehyde solution buffered with 10% borax and stained with rose bengal. The specimens of Prionospio were sorted and examined using a light microscope in the laboratory and transferred to 70% ethanol. Some material was conserved directly in 96% ethanol and was previously used for phylogenetics and the delimination of the species (Hektoen et al. 2024). After examination, the newly collected material was deposited in the collections of the Norwegian University of Science and Technology, NTNU University Museum (NTNU-VM) (Bakken et al. 2025). Museum collections, including specimens from outside of northern Europe, and existing types of most northern European species of Prionospio, were also studied. In total, approximately 2500 specimens of Prionospio spp. were examined. In the Taxonomy section below, species are listed alphabetically, except for Prionospio cf. sanmartini which is discussed before Prionospiofiordicasp. nov., and P. multisetosa which is placed after P. dubia. In the Material examined section, specimens previously sequenced by Hektoen et al. (2024) are listed separately. A list of museums and their acronyms holding the samples which are reported in this study is given below. Institutional abbreviations LACM-AHF = Allan Hancock Foundation Polychaete Collection, Natural History Museum of Los Angeles County, USA MNCN = National Museum of Natural History, Madrid, Spain NHMO = Natural History Museum, University of Oslo, Oslo, Norway NTNU-VM = NTNU University Museum, Trondheim, Norway SMNH = Swedish Natural History Museum, Stockholm, Sweden UPSZTY = Museum of Evolution, Uppsala, Sweden USNM = National Museum of Natural History, Washington DC, USA ZMBN = University Museum of Bergen, University of Bergen, Bergen, Norway For morphology, specimens were stained with a water solution of Methylene Green, Zinc Chloride Double Salt (Chroma) to increase contrast, and then studied using a compound microscope equipped with a digital camera LEICA DMC5400. Twenty-five specimens were dehydrated using a critical point European Journal of Taxonomy 1027: 1–58 (2025) 4 dryer, mounted on stubs, sputter coated with gold-palladium and then examined using a Teneo Scanning Electron Microscope (SEM) at NTNU Cellular & Molecular Imaging Core Facility (CMIC). Due to the lack of complete specimens, for size estimates, we used the width of the specimens on the 10th chaetiger. Plates and line drawings were created and edited in Adobe Photoshop ver. 24.3.0. The morphological terminology used for the descriptions of the species follows that of Radashevsky (2012). A list of abbreviations used to mark morphological details on the figures is given below. Morphological abbreviations br = branchia ca = caruncle ch = chaetiger ci = cilia cr = dorsal crest es = esophagus fo = dorsal fold lc = dorsolateral longitudinal ciliation ls = lateral swelling me = median eye ne = neuropodial postchaetal lamella no = notopodial postchaetal lamella nu = nuchal organ pa = palp pe = peristomium pe+ch1 = fold formed by fusion of posterior dorsolateral part of peristomium and notopodial postchaetal lamella of chaetiger 1 pr = prostomium sa = sabre chaeta sc = scar Results Taxonomy Phylum Annelida Lamarck, 1809 Class Polychaeta Grube, 1850 Family Spionidae Grube, 1850 Genus Prionospio Malmgren, 1867 Prionospio Malmgren, 1867: 201. Prionospio – Blake & Kudenov 1978: 211–212. — Maciolek 1985: 325–283. — Blake et al. 2020: 61–62. Type species Prionospio steenstrupi Malmgren, 1867, by monotypy. Diagnosis Prostomium anteriorly rounded to truncate, with frontal margin entire to weakly incised, rarely with fronto-lateral horns; subtriangular, rectangular or oval in shape, extending posteriorly at least to end of chaetiger 1 as a low caruncle. Nuchal organs U-shaped lateral to caruncle. Red, rarely black eyes HEKTOEN M.M. et al., Partial revision of Northern European Prionospio (Annelida: Spionidae) 5 present or absent. Occipital antenna absent. Peristomium at least partially fused with notopodial postchaetal lamellae of chaetiger 1, forming low wings to prominent ear-shaped structures on lateral sides of prostomium. Notopodial lamellae of chaetiger 1 small, usually fused with dorsal posterior parts of peristomium; neuropodia lamellae small. Notoand neuropodial postchaetal lamellae largest on branchiate chaetigers, reduced thereafter. Notopodial lamellae on postbranchiate chaetigers often interconnected by dorsal transverse low ridges to high crests. Interparapodial pouches or membranous folds present or absent. Branchiae usually from chaetiger 2, rarely from chaetiger 3 or absent, limited to anterior part of body, cylindrical or flattened with surfaces perpendicular to body axis, free from notopodial lamellae, smooth, apinnate or with digitiform pinnules. Hooks bi-, tri-, quadrior multidentate, with inner and / or rarely only outer hoods, present in notoand neuropodia; shaft slightly curved, without constriction. Sabre chaetae usually present in neuropodia, rarely absent. Pygidium with one long middorsal cirrus and two shorter ventral cirri; rarely ventral cirri reduced. Remarks This diagnosis mainly follows that of Blake et al. (2020), with addition of characters described by Radashevsky (2012) and as required by accommodation of Prionospio cerastae Radashevsky, 2015 which has fronto-lateral horns on the prostomium. Prionospio banyulensis Laubier, 1966 Figs 2–3 Prionospio banyulensis Laubier, 1966: 258. Prionospio ockelmanni Pleijel, 1985: 177–181, figs 1–3. Prionospio banyulensis – Laubier 1968: 99–105, figs 10–15. — Sigvaldadóttir 1992: 210–217, figs 1–5, table 1. — Kirkegaard 1996: 79, fig. 35. — Hektoen et al. 2024: figs 1, 4. Prionospio (Minuspio) banyulensis – Hartmann-Schröder 1996: 328–329. Aurospio banyulensis – Sigvaldadóttir 1998: 186. — Sigvaldadóttir 2002: 210. Diagnosis Prostomium anteriorly rounded, posteriorly extending to end of chaetiger 1 as a short, thick caruncle. Median eyes large, crescentic. Three pairs of apinnate branchiae on chaetigers 3–5 similar in size to notopodial postchaetal lamellae. Neuropodial lamellae of chaetiger 2 quadrangular, upwards-turned, of chaetiger 3 subrectangular, upwards-turned. Sabre chaetae in neuropodia from chaetiger 10. Hooded hooks in neuropodia from chaetigers 11–14. Type material of Prionospio banyulensis Neotype FRANCE • Banyuls-sur-Mer, Cap d’Osne; 42°29.8′ N, 3°8.48′ E; depth 24 m; 9. Oct. 1991; stn Banyuls1991h; van Veen grab; designated by Sigvaldadóttir (1992); SMNH Type-4422. Type material of Prionospio ockelmanni Holotype SWEDEN • Öresund; depth 29 m; 11 Sep. 1976; Fredrik Pleijel leg.; stn Öresund1976; SMNH Type3358. Paratypes SWEDEN • 3 specs; Öresund; depth 29 m; 11 Sep. 1976; Fredrik Pleijel leg.; stn Öresund1976; SMNH Type-3358. European Journal of Taxonomy 1027: 1–58 (2025) 6 Other material examined FRANCE • 1 spec.; Banyuls-sur-Mer, Coralligene; 42°30.220′ N, 3°8.300′ E; depth 18 m; 14 Jan. 1991; stn Banyuls1991f; van Veen grab; SMNH 111890 • 1 spec.; Banyuls-sur-Mer; Arne Nygren leg.; stn 257; NTNU-VM 84125 • 3 specs; Banyuls-sur-Mer; Fredrik Pleijel leg.; 1 Oct. 1993; LACM-AHF Poly 4424. NORWAY – Møre og Romsdal • 1 spec.; Smøla, Andholman; 63°28.017′ N, 7°51.455′ E; depth 22 m; 17 Dec. 2019; Åkerblå AS leg.; stn AND-7; van Veen grab; NTNU-VM 84030. – Trøndelag • 1 spec.; Hitra Singsholmen; 63°24.876′ N, 8°25.368′ E; depth 41 m; 18 Nov. 2020; Åkerblå AS leg.; stn SIN-2; van Veen grab; SEM stub; NTNU-VM 84148 • 1 spec.; same data as for preceding; NTNU-VM 84035 • 1 spec.; Frøya, Olaugsskjæret; 63°47.664′ N, 8°31.230′ E; depth 36 m; 6 Nov. 2019; Åkerblå AS leg.; stn OLA-1; van Veen grab; NTNU-VM 84026 • 4 specs; Bjugn Havsund; 63°48.073′ N, 9°26.799′ E; depth 22 m; 27 Aug. 2019; Åkerblå AS leg.; stn HAV-3; van Veen grab; NTNU-VM 84024 • 1 spec.; Frøya, Tennøya; 63°48.327′ N, 8°27.493′ E; depth 120 m; 13 Aug. 2020; Åkerblå AS leg.; stn TEN-4; van Veen grab; SEM stub; NTNU-VM 84147 • 7 specs; Steinskjær Tjuin; 64°4.367′ N, 11°14.203′ E; depth 25 m; 16 Jul. 2020; Åkerblå AS leg.; stn TJU-3; van Veen grab; NTNU-VM 84036 • 1 spec.; same data as for preceding; SEM stub; NTNU-VM 84149 • 1 spec.; Frøya, Kya; 63°46.216′ N, 8°19.535′ E; depth 41 m; 27 Jul. 2022; stn Kya-5; van Veen grab; NTNU-VM 84142. – Nordland • 3 specs; Herøy, Nordgåsvær; 66°4.639′ N, 12°4.353′ E; depth 75 m; 27 Sep. 2021; Åkerblå AS leg.; stn NGÅ-2; van Veen grab; NTNU-VM 84031. – Troms • 5 specs; Tranøy, Hallvarsøya; 69°9.284′ N, 16°54.531′ E; depth 60 m; 29 Oct. 2019; Åkerblå AS leg.; stn HAL-4; van Veen grab; NTNU-VM 84023 • 1 spec.; Senja, Ørnfjordbotn; 69°29.640′ N, 17°39.969′ E; depth 80 m; 14 Jul. 2021; Åkerblå AS leg.; stn ØRN-3; van Veen grab; NTNU-VM 84025 • 1 spec.; Karlsøy, Korsnes; 69°59.065′ N, 19°55.377′ E; depth 101 m; 18 Sep. 2019; Åkerblå AS leg.; stn KOR-1; van Veen grab; SEM stub; NTNU-VM 84150 • 1 spec.; same data as for preceding; SEM stub; NTNU-VM 84151 • 2 specs; Karlsøy, Karanes; 70°4.132′ N, 19°18.715′ E; depth 73 m; 11 Aug. 2021; Åkerblå AS leg.; stn KAR-4; van Veen grab; NTNU-VM 84068 • 1 spec.; Karlsøy, Mjønes; 70°6.477′ N, 19°35.958′ E; depth 216 m; 7 Dec. 2021; Åkerblå AS leg.; stn MJØ-3; van Veen grab; NTNU-VM 84072 • 4 specs; Tromsø, Nordnibba; 70°9.855′ N, 19°21.322′ E; depth 73 m; 11 Oct. 2021; Åkerblå AS leg.; stn NOR-REF; van Veen grab; NTNU-VM 84034 • 2 specs; Tromsø, Nordnibba; 70°9.993′ N, 19°22.469′ E; depth 67 m; 11 Oct. 2021; Åkerblå AS leg.; stn NOR5; van Veen grab; NTNU-VM 84033. – Finnmark • 2 specs; Alta, Langnes; 70°6.537′ N, 23°0.061′ E; depth 26 m; 22 Jun. 2022; Åkerblå AS leg.; stn LAN-1; van Veen grab; NTNU-VM 84066 • 11 specs; Hammerfest, Bårdfjord; 70°25.701′ N, 22°51.086′ E; depth 61 m; 3 Nov. 2021; Åkerblå AS leg.; stn BÅR-REF; van Veen grab; NTNU-VM 84032. SWEDEN – Halland • 1 spec.; Varberg, Värö; 57°10.000′ N, 12°5.000′ E; depth 20 m; 1980; stn Varö spring 1980 2; van Veen grab; SMNH 9556. – Bohuslän • 2 specs; Stora Fjädern; depth 35 m; stn St. Fjädern; SMNH 111891 • 1 spec.; Väderöarna, SE of Hamnerö; depth 22–30 m; 10 Jul 1984; SMNH 111892 • 1 spec.; Kostergrund; depth 40 m; 29 Jun 1990; stn Koster1991; SMNH 111894. UNITED KINGDOM • 5 specs; Plymouth, Stoke point, Millbay channel; depth 35–40 m; 6 Jun. 1986; stn Ply1986i; SMNH 111878. Examined material with sequence data FRANCE • 1 spec.; Banyuls sur Mer; leg. Arne Nygren leg.; stn 256; NTNU-VM 84037. NORWAY – Viken • 1 spec.; Drøbak; 59°38.694′ N, 10°36.702′ E; depth 125–130 m; 22 Oct. 2014; POLYSKAG exped.; stn POLYSKAG-2014/10-19; dredge; ZMBN 152614. — Finnmark • 1 spec.; Hammerfest Borvika; 70°44.517′ N, 23°25.965′ E; depth 49 m; 26 Aug. 2020; Åkerblå AS leg.; stn BOR-REF; van Veen grab; NTNU-VM 84027 • 1 spec.; same data as for preceding; NTNU-VM 84028 HEKTOEN M.M. et al., Partial revision of Northern European Prionospio (Annelida: Spionidae) 7 • 1 spec.; Hammerfest, Borvika; 70°45.454′ N, 23°26.833′ E; depth 46 m; 26 Aug. 2020; Åkerblå AS leg.; stn BOR-2; van Veen grab; NTNU-VM 84029. Description (adults) Neotype (SMNH Type-4422) complete, 7 mm long, 0.15 mm wide, with 47 chaetigers, laterally flattened, likely due to previously being mounted on slide. Other complete specimens up to 12.6 mm long, 0.4 mm wide, with up to 65 chaetigers. Color in alcohol pale white. Prostomium anteriorly broadly rounded, posteriorly extending to end of chaetiger 1 as a thick caruncle (Fig. 2A). Nuchal organs U-shaped ciliary bands lateral to caruncle. Two pairs of eyes arranged trapezoidally, bright red in alcohol, red to dark brown in formalin, color fading during storage in alcohol. Median eyes large, crescentto oval-shaped; lateral eyes large round spots, situated anteriorly and set wider apart. Dorsolateral parts of peristomium fused with notopodial postchaetal lamellae of chaetiger 1, forming ear-shaped structures lateral to prostomium (Fig. 2A). Palps missing in neotype, in other specimens as long as 10–15 chaetigers. Fig. 2. Adult morphology of Prionospio banyulensis Laubier, 1966. A–B. SEM micrographs. C–F. Line drawings of parapodia. A. Anterior end, dorsal view (NTNU-VM 84148). B. Neuropodium of chaetiger 10, showing two vertical rows of capillary chaetae and two inferior sabre chaetae (NTNU-VM 84148). Scale bars: A = 100 µm; B = 20 µm; C–F = 100 µm. European Journal of Taxonomy 1027: 1–58 (2025) 8 Branchiae on chaetigers 3–5, apinnate, with dense ciliation on lateral edges, approximately equal in size, slightly longer than notopodial postchaetal lamellae (Fig. 2A, 3A). Nototrochs transverse ciliary bands on chaetiger 2 and between bases of branchiae of chaetigers 3 and 4. Dorsolateral longitudinal ciliation absent. Notopodial prechaetal lamellae small, rounded on chaetigers 2 and 3, inconspicuous on succeeding chaetigers. Notopodial postchaetal lamellae of chaetiger 1 fused with dorsal posterior parts of peristomium; lamellae subrectangular on chaetiger 2, largest on chaetigers 3 and 4, sometimes with short tips on branchiate chaetigers (Figs 2A, C–D), smaller on postbranchiate chaetigers (Figs 2A, 3A), oval from chaetigers 7–8 onwards. Low dorsal crests present between notopodial lamellae from chaetigers 6–9 to chaetigers 10–15 (Figs 2A, 3A). Neuropodial prechaetal lamellae inconspicuous. Neuropodial postchaetal lamellae of chaetiger 1 small and oblong, of chaetiger 2 subtriangular, higher than long and slightly upwards-pointed (Fig. 2C), of chaetiger 3 triangular with upwards-pointed tip (Fig. 2D), rounded, small from chaetiger 4 onwards (Fig. 2E–F). Interneuropodial pouches absent. Notopodial capillaries on anterior chaetigers arranged in two rows, unilimbate and slightly granulated. Anterior row shorter than posterior row. Notopodial capillaries in middle and posterior chaetigers alimbate, long, thin, sometimes coiled. Neuropodial capillaries arranged in two rows on anterior chaetigers unilimbate, granulated, anterior row shorter than posterior row. Sabre chaetae in neuropodia from chaetiger 10, with slight granulation on distal part, one or rarely two per fascicle (Fig. 2B). Hooded hooks in notopodia from chaetigers 23–43; in neuropodia from chaetigers 12–14, up to nine in a series, alternating with 1–3 capillary chaetae. Both notoand neuropodial hooks with 4–5 pairs of upper teeth arranged in two vertical rows above main fang, with outer and inner hoods. Pygidium with one long middorsal cirrus and one pair of short ventral cirri. Reproduction Prionospio banyulensis is dioecious. Of the 12 sexually mature individuals studied, seven were males and five were females. The smallest mature worms had about 45 chaetigers. In both females and males, gametes develop from chaetiger 10 to chaetigers 33–60. Spermatids were interconnected in tetrads; spermatozoa were ect-aquasperm with spherical nucleus about 2 µm in diameter. Largest oocytes were about 70 µm in diameter, with smooth envelope about 2 µm thick having single depression about 10 µm in diameter and 5-6 µm deep; nucleus was about 27 µm in diameter, with a single nucleolus about 8 µm in diameter. The mature individuals had notopodial capillaries essentially longer than capillaries in juveniles, indicating possible swimming and swarming during spawning event. Remarks Prionospio banyulensis was originally described from Banyuls-sur-Mer, Mediterranean Sea, France. Laubier (1966) first provided brief notes about the ecology of P. banyulensis and then described the morphology of this species (Laubier 1968) but never designated type specimens. Sigvaldadóttir (1992) redescribed P. banyulensis, designated a neotype, and for the first time reported the species from northern Europe. Moreover, Sigvaldadóttir (1992) treated Prionospio ockelmanni Pleijel, 1985, described from Öresund, Sweden, as a junior synonym of P. banyulensis. Based on the results of a phylogenetic analysis of morphological characters of the species of the Prionospio-complex, where P. banyulensis formed a monophyletic group with Aurospio dibranchiata, Sigvaldadóttir (1998) transferred P. banyulensis to Aurospio. Blake et al. (2020: 59) noted that some species of Prionospio have erroneously been assigned to Aurospio “based almost entirely on the first occurrence of branchiae from chaetiger 3 instead of chaetiger 2”. They proposed that several species listed among Aurospio should be referred to Prionospio but did not act at that time. Hektoen et al. (2024) moved banyulensis back to Prionospio according to the results of a phylogenetic analysis of molecular data and noted that the remaining species of Aurospio HEKTOEN M.M. et al., Partial revision of Northern European Prionospio (Annelida: Spionidae) 9 should be further studied. Our re-examination of the types of P. banyulensis and P. ockelmanni supports their conspecificity. The neotype of P. banyulensis is not imaged here as camera-equipped microscopes were not available at SMNH. Sigvaldadóttir (1992) found specimens of P. banyulensis with two and three pairs of branchiae from chaetiger 3. We examined a greater number of specimens than in previous studies, some of larger sizes than previously reported. We found specimens with a greater variation in branchial configuration that potentially belongs to P. banyulensis. In addition to dibranchiate (two pairs) and tribranchiate (three pairs) specimens, worms with four (Fig. 3B, D) and five pairs of branchiae occurred. All worms with more than three pairs of branchiae were found from Norwegian coastal waters, while specimens with two and three pairs of branchiae occurred in both Norway and the type locality of Banyuls. No other differences in morphological characters were apparent, and the specimens with 4 and 5 pairs of branchiae were always found together with P. banyulensis with three pairs of branchiae, and were generally larger in size, indicating the number of branchiae could be a size related character. In dibranchiate specimens, Fig. 3. Adult morphology of Prionospio banyulensis Laubier, 1966. A–C. SEM micrographs. D. Light microscope image. A. Anterior end, dorsal view, showing three pairs of branchiae from chaetiger 3 (NTNU-VM 84151). B. Anterior end, left lateral view, showing four pairs of branchiae from chaetiger 2 (NTNU-VM 84147). C. Anterior end, left lateral view, showing three pairs of branchiae from chaetiger 2 (NTNU-VM 84150). D. Anterior end stained with methylene green, left dorsolateral view, showing four pairs of branchiae from chaetiger 2 (NTNU-VM 84023). Abbreviations: see Material and methods. Scale bars = 100 µm. European Journal of Taxonomy 1027: 1–58 (2025) 16 Slettnes Vest; 62°57.660′ N, 7°50.739′ E; depth 135 m; 27 May 2021; Åkerblå AS leg.; stn SLE-REF; van Veen grab; NTNU-VM 84014 • 5 specs; Gjemnes, Slettnes Vest; 62°57.670′ N, 7°51.966′ E; depth 163 m; 27 May 2021; Åkerblå AS leg.; stn SLE-5; van Veen grab; NTNU-VM 84013 • 1 spec.; Tingvoll, Halsbukta; 63°4.952′ N, 8°8.815′ E; depth 343 m; 2 Jun. 2021; Åkerblå AS leg.; stn hal-3; van Veen grab; NTNU-VM 84011 • 1 spec.; Tingvoll, Halsbukta; 63°4.219′ N, 8°8.888′ E; depth 304 m; 2 Jun. 2021; Åkerblå AS leg.; stn hal-4; van Veen grab; SEM stub; NTNU-VM 84153 • 1 spec.; same data as for preceding; NTNU-VM 84012 • 9 specs; Averøy, Skjellingen; 63°8.698′ N, 7°33.211′ E; depth 111 m; 5 Jul. 2021; Åkerblå AS leg.; stn SKJ-1.4; van Veen grab; NTNU-VM 84017 • 1 spec.; Aure Hagahammaren; 63°8.027′ N, 8°1.332′ E; depth 207 m; 22 May 2019; Åkerblå AS leg.; stn HAG-2; van Veen grab; SEM stub; NTNU-VM 84155 • 1 spec.; same data as for preceding; NTNU-VM 83992 • 5 specs; Aure, Hagahammaren; 63°8.187′ N, 8°2.185′ E; depth 213 m; 22 May 5 2019; Åkerblå AS leg.; stn HAG-5; van Veen grab; NTNU-VM 83991. – Trøndelag • 1 spec.; Hitra, Værøya; 63°24.700′ N, 8°28.885′ E; depth 205 m; 21 May 2021; Åkerblå AS leg.; stn VÆR-REF; van Veen grab; SEM stub; NTNU-VM 84154 • 4 specs; same data as for preceding; NTNU-VM 84018 • 6 specs; Indre Fosen, Frengåsen; 63°42.106′ N, 9°52.857′ E; depth 91 m; 23 Jun. 2021; Åkerblå AS leg.; stn FRE-2; van Veen grab; NTNU-VM 83994 • 1 spec.; Indre Fosen, Frengåsen; 63°42.157′ N, 9°53.129′ E; depth 98 m; 23 Jun. 2021; Åkerblå AS leg.; stn FRE-3.2; van Veen grab; NTNU-VM 83995 • 4 specs; Indre Fosen, Frengåsen; 63°42.210′ N, 9°53.399′ E; depth 120 m; 23 Jun. 2021; Åkerblå AS leg.; stn FRE-1; van Veen grab; NTNU-VM 83993 • 2 specs; Indre Fosen, Frengåsen; 63°42.334′ N, 9°53.802′ E; depth 162 m; 23 Jun. 2021; Åkerblå AS leg.; stn FRE-4; van Veen grab; NTNU-VM 83996 • 1 spec.; Indre Fosen, Frengåsen; 63°42.436′ N, 9°53.802′ E; depth 196 m; 23 Jun. 2021; Åkerblå AS leg.; stn FRE-5.1; van Veen grab; NTNU-VM 83997 • 1 spec.; Skjoldryggen; 65°30.034′ N, 6°16.109′ E; depth 397 m; 23 Jun. 2013; MAREANO leg.; stn R1119-67; van Veen grab; ZMBN 152585. – Troms • 1 spec.; Tranøy, Gjervika; 69°2.628′ N. 16°51.239′ E; depth 160 m; 30 Oct. 2019; Åkerblå AS leg.; stn GJE-REF; van Veen grab; NTNU-VM 83999 • 1 spec.; Tranøy Gjervika; 69°2.796′ N, 16°53.047′ E; depth 250 m; 30 Oct. 2019; Åkerblå AS leg.; stn GJE-4.1; van Veen grab; SEM stub; NTNU-VM 84152 • 4 specs; same data as for preceding; NTNU-VM 83998. SENEGAL • 3 specs; 14°27.576′ N, 17°36.624′ W; depth 489 m; 5 Nov. 2011; CCLME exped.; stn 2011410-GR08; van Veen grab; ZMBN 152596 • 3 specs; 15°28.812′ N, 17°13.566′ W; depth 504 m; 7 Nov. 2011; CCLME exped.; stn 2011410-GR09; van Veen grab; ZMBN 152588. SWEDEN • 1 spec.; Varberg, Värö; 57°10′ N, 12°1′ E; depth 47 m; 1981; stn VÄRH81#3; van Veen grab; SMNH 11281 • 1 spec.; same data as for preceding; 1978; stn VÄRH78#3; van Veen grab; SMNH 8105 • 1 spec.; same data as for preceding; SMNH 6450 • 1 spec.; same data as for preceding; 1979; stn VÄRV79#3; van Veen grab; SMNH 9009 • 1 spec.; same data as for preceding; SMNH 8716 • 2 specs; same data as for preceding; 1980; VÄRV80#3; van Veen grab; SMNH 9667 • 3 specs; same data as for preceding; 1984; VÄRV84#3; van Veen grab; SMNH 53676. WESTERN SAHARA • 1 spec.; 25°3.900′ N, 16°18.612′ W; depth 568 m; 25 Nov. 2011; CCLME exped.; stn 2011410-GR20; van Veen grab; ZMBN 152587 • 19 specs; 26°27.402′ N, 14°30.612′ W; depth 435 m; 29 Nov. 2011; CCLME exped.; stn 2011410-GR24; van Veen grab; ZMBN 152595. Examined material with sequence data GUINEA • 1 spec.; 9°38.724′ N, 16°40.002′ W; depth 509 m; 15 May 2012; CCLME exped.; stn 2012404-GR03; van Veen grab; ZMBN 152594. MAURITANIA • 1 spec.; 16°22.698′ N, 16°51.972′ W; depth 509 m; 8 Nov. 2011; CCLME exped.; stn 2011410-GR10; van Veen grab; ZMBN 152602 • 1 spec.; 17°20.538′ N, 16°46.590′ W; depth 572 m; 1 Jun. 2012; CCLME exped.; stn 2012404-GR28; van Veen grab; ZMBN 114671. HEKTOEN M.M. et al., Partial revision of Northern European Prionospio (Annelida: Spionidae) 17 MOROCCO • 1 spec.; 28°52.026′ N, 12°34.176′ W; depth 495 m; 6 Jun. 2011; CCLME exped.; stn 2011410-GR35; van Veen grab; ZMBN 152581 • 1 spec.; 33°46.164′ N, 7°41.424′ W; depth 99 m; 15 Nov. 2011; CCLME exped.; stn 2011410-GR55; van Veen grab; ZMBN 152759. NORWAY – Norwegian Sea • 1 spec.; 61°13.050′ N, 2°16.677′ E; depth 218 m; 28 May 2014; stn GFC-30; van Veen grab; ZMBN 152598 • 1 spec.; 61°22.629′ N, 2°6.581′ E; depth 284 m; 28 May 2011; stn VGPT2-10_2011; van Veen grab; ZMBN 152583. – Akershus • 1 spec.; Drøbak; 59°38.664′ N, 10°37.152′ E; depth 100–106 m; 20 Oct. 2014; POLYSKAG leg.; stn POLYSKAG2014/10-4; sledge; ZMBN 152603. – Rogaland • 1 spec.; Stavanger, Boknafjorden; 59°12.833′ N, 5°46.519′ E; depth 168 m; 10 Jun. 2014; Bergen University Museum leg.; stn HM2014/06-56; van Veen grab; ZMBN 152584 • 1 spec.; Sandnes Strand; 58°56.913′ N, 5°59.179′ E; depth 250–251 m; 10 Jun. 2014; Bergen University Museum leg.; stn HM2014/06-43; sledge; ZMBN 152589. – Vestland • 1 spec.; Øygarden Nautnes; 60°37.544′ N, 4°39.917′ E; depth 253 m; 1 May 2017; Bergen University Museum leg.; stn KB66; van Veen grab; ZMBN 152601 • 1 spec.; Øygarden, Sund; 60°11.061′ N, 5°11.737′ E; depth 665 m; 26 Apr. 2017; Bergen University Museum leg.; stn KB-03; van Veen grab; ZMBN 152599 • 1 spec.; Aurland Aurlandsvangen; 60°54.233′ N, 7°10.088′ E; depth 115 m; 17 Nov. 2012; Bergen University Museum leg.; stn HM2012-11-12; van Veen grab; ZMBN 152597 • 1 spec.; Selje, Beitveit; 62°8.171′ N, 5°19.906′ E; depth 138 m; 10 Oct. 2019; Åkerblå AS leg.; stn BEI-3; van Veen grab; SEM stub; NTNUVM 83989. – Trøndelag • 1 spec.; Ørland, Brekstad; 63°39.444′ N, 9°38.025′ E; depth 260–278 m; 24 Oct. 2016; stn 2016041; sledge; ZMBN 114364 • 1 spec.; Haltenbanken; 64°8.214′ N, 8°43.170′ E; depth 233 m; 5 Oct. 2013; MAREANO leg.; stn R890-105; van Veen grab; ZMBN 152600 – Troms • 1 spec.; Tranøy, Gjervika; 69°2.628′ N. 16°51.239′ E; depth 250 m; 30 Oct. 2019; Åkerblå AS leg.; stn GJE-4; van Veen grab; NTNU-VM 83990. REPUBLIC OF THE CONGO • 1 spec. 4°29.616′ S, 10°55.878′ E; depth 202 m; 12 May 2008; GCLME exped.; stn 8CR-01; van Veen grab; ZMBN 114799. SENEGAL • 1 spec.; 15°28.812′ N, 17°13.566′ W; depth 504 m; 7 Nov. 2011; CCLME exped.; stn 2011410-GR09; van Veen grab. WESTERN SAHARA • 1 spec.; 26°27.402′ N, 14°30.612′ W; depth 435 m; 29 Nov. 2011; CCLME exped.; stn 2011410-GR24; van Veen grab; ZMBN 152592. Comparative material Prionospio gayheadia Delgado-Blas & Peraza, 2024 UNITED STATES – Massachusetts • > 25 specs; 40°1.248′ N, 70°55.086′ W; depth 250 m; 4 May 1985; Battelle-New England Marine Lab For BLM/ MMS leg.; USNM 1002841 • > 25 specs;same data as for preceding; USNM 1002842 • > 25 specs; 40°1.302′ N, 70°55.098′ W; depth 250 m; 4 May 1985; Battelle-New England Marine Lab For BLM/ MMS leg.; USNM 1002843 • 2 specs; Georges Bank, Lydonia Canyon; 40°27.468′ N, 67°40.266′ W; depth 556 m; 6 Jul. 1985; Battelle-New England Marine Lab For BLM/ MMS leg.; USNM 1002845 • 1 spec.; 39°48.252′ N, 70°54.948′ W; depth 1273 m; 30 Jul. 1986; Battelle-New England Marine Lab For BLM/ MMS leg.; USNM 1002854 • 1 spec.; 30°3.420′ N, 88°38.080′ W; depth 20 m; 20 Aug. 1988; D. Harper leg.; box corer; USNM 1573961 • 2 specs; 29°4.932′ N, 88°45.516′ W; depth 150 m; 11 Mar. 1988; D. Harper leg.; box corer; USNM 1573962 • 1 spec.; 29°16.302′ N, 88°6.498′ W; depth 150 m; 21 Aug. 1988; D. Harper leg.; box corer; USNM 1573963 • 1 spec.; 29°16.302′ N, 88°6.498′ W; depth 150 m; 16 Mar. 1988; D. Harper leg.; box corer; USNM 1573964 • 3 specs; 29°42.084′ N, 87°20.166′ W; depth 100 m; 13 Mar. 1988; D. Harper leg.; box corer; USNM 1573965. – Florida • 1 spec.; 29°40.500′ N, 89°16.002′ W; depth 200 m; 23 Aug. 1988; D. Harper leg.; box corer; USNM 1573982 • 2 specs; 29°42.084′ N, 87°20.166′ W; depth 100 m; 16 Mar. 1988; D. Harper leg.; box corer; USNM 1573983 • 2 specs; same data as for European Journal of Taxonomy 1027: 1–58 (2025) 18 preceding; USNM 1573987 • 1 spec.; 30°2.118′ N, 88°38.082′ W; depth 20 m; 19 Aug. 1988; D. Harper leg.; box corer; USNM 1573984 • 1 spec.; 30°2.118′ N, 88°38.082′ W; depth 20 m; 12 Mar. 1988; D. Harper leg.; box corer; USNM 1573985 • 1 spec.; same data as for preceding; USNM 1573986 • 1 spec.; 29°24.000′ N, 88°7.002′ W; depth 100 m; 17 Mar. 1988; D. Harper leg.; box corer; USNM 1573988 • 1 spec.; 29°42.084′ N, 87°20.166′ W; depth 100 m; 22 Aug. 1988; D. Harper leg.; box Fig. 6. Adult morphology of Prionospio multisetosa Delgado-Blas & Peraza, 2024. A–B. SEM micrographs. C. Light microscope image. A. Anterior end, dorsal view (NTNU-VM 84156). B. Anterior end, dorsal view (NTNU-VM 84152). C. Anterior end stained with methylene green, left lateral view (NTNU-VM 84000). Abbreviations: see Material and methods. Scale bars = 200 µm. HEKTOEN M.M. et al., Partial revision of Northern European Prionospio (Annelida: Spionidae) 19 corer; USNM 1573989 • 3 spec.; 29°24.000′ N, 88°7.002′ W; depth 100 m; 20 Aug. 1988; D. Harper leg.; box corer; USNM 1573990 • 3 specs; same data as for preceding; USNM 1573991 • 2 specs; 29°42.084′ N, 87°20.166′ W; depth 100 m; 16 Mar. 1988; D. Harper leg.; box corer; USNM 1573992 • 3 specs; 29°40.500′ N, 89°16.002′ W; depth 200 m; 23 Aug. 1988; D. Harper leg.; box corer; USNM 1573993 • 1 spec.; 29°48.000′ N, 87°22.800′ W; depth 40 m; 16 Mar. 1988; D. Harper leg.; box corer; USNM 1573994 • 1 spec.; 29°24.000′ N, 88°7.002′ W; depth 100 m; 20 Aug. 1988; D. Harper leg.; box corer; USNM 1573995 • 2 specs; 29°14.898′ N, 88°7.284′ W; depth 200 m; 20 Aug. 1988; D. Harper leg.; box corer; USNM 1573996. Remarks Prionospio multisetosa was described by Delgado-Blas & Peraza (2024) during the preparation of the present manuscript. We were not able to examine the type material, and given the thorough and detailed original description, we did not find it necessary to provide a full redescription here. Instead, we present additional observations based on a larger number of specimens from a broader geographic and bathymetric range, contributing further information on the intraspecific variability and distribution of the species. Delgado-Blas & Peraza (2024) based the description of P. multisetosa on 15 specimens from the west coast of Sweden, which they compared with the descriptions (not specimens) of P. dubia from South Africa provided by Day (1961) and Wilson (1990). Earlier, Prionospio with same characteristics from northern Europe were referred by various authors to P. dubia (Sigvaldadóttir & Mackie 1993; Sigvaldadóttir 2002). Delgado-Blas & Peraza (2024: table 1) noticed that the described South African Fig. 7. Parapodia and chaetal morphology of Prionospio multisetosa Delgado-Blas & Peraza, 2024 (NTNU-VM 84022). A–F. Posteriorly facing parapodia of chaetigers 1–5 and 10. G. Hooded hook from neuropodium of chaetiger 20. H. Sabre chaeta from neuropodium of chaetiger 20. Abbreviations: see Material and methods. Scale bars: A–F = 100 μm; G–H = 10 μm. European Journal of Taxonomy 1027: 1–58 (2025) 20 specimens of P. dubia had 26–50 chaetigers while Swedish specimens, which they described as P. multisetosa, had 60–98 chaetigers, despite that all worms from South Africa were anterior fragments. They noted a series of morphological characters to distinguish P. multisetosa and P. dubia: presence or absence of eyes, size of the branchiae, position of the pinnules on the branchiae of chaetiger 5, whether the notopodial postchaetal lamellae extend slightly onto the dorsum or not, size of the notopodial prechaetal lamellae, shape of the notopodial postchaetal lamellae of chaetiger 3, shape of the neuropodial capillaries of chaetigers 2–5, the appearance and shape of sabre chaetae and the notopodial and neuropodial hooded hooks. In this study, we examined 313 specimens previously identified as P. dubia from northern Norway south to the Republic of the Congo and could not find any morphological differences between Nordic and West African worms. We provide more insight into the intraspecific variation in P. multisetosa, and new images of anterior morphology (Fig. 6A–C) and drawings of parapodia and chaetae (Fig. 7A–H) of this species. We found some specimens with branchiae of chaetiger 2 extending to chaetiger 9, rather than to chaetiger 5, as reported by Delgado-Blas & Peraza (2024) for North Atlantic specimens, and that the branchiae of chaetigers 3 and 4 are similar in length to the notopodial postchaetal lamellae on the same chaetiger rather than shorter (Fig. 7C–D). While it was common for the notopodial postchaetal lamellae of chaetiger 2 to have a short ventral edge, not all worms had lamellae shaped like this. The neuropodial lamellae of chaetiger 3 were dorsally pointed in most worms (Fig. 8C), which was not clearly expressed or illustrated in the original description of P. multisetosa by Delgado-Blas & Peraza (2024). We also found slightly larger ranges of the first appearance of hooded hooks and sabre chaetae in neuropodia. The smallest juveniles (0.1 mm wide) had hooded hooks in neuropodia from chaetiger 14 and sabre chaetae from chaetiger 13. In comparison, Delgado-Blas & Peraza (2024) reported the first appearance of hooded hooks and sabre chaetae in neuropodia from chaetigers 16 and 14, respectively, likely due to their studying slightly larger specimens (0.2 mm wide). The studied material includes all specimens sequenced by Hektoen et al. (2024), which came from the same broad geographic range, from northern Norway to the Republic of the Congo, and depths from 106 m to 665 m. Their molecular analysis confirmed their conspecificity. To summarize, we observed a wide range of ontogenetic variability of specimens with diagnostic characters of P. dubia but could not find distinct morphological differences between them to assume the presence of more than one species. Our previous molecular analysis confirmed the conspecificity of worms collected from northern Norway south to the Republic of the Congo (Hektoen et al. 2024). This wide distribution range combined with the minute morphological differences between P. dubia and P. multisetosa may indicate that P. multisetosa is a junior synonym of P. dubia. However, this will likely only be resolved once new material of P. dubia from South Africa is collected and sequenced. Habitats and distribution Originally, P. multisetosa was reported from the west coast of Sweden. Here, we provide additional records of this species from East Atlantic waters, from northern Norway south to the Republic of the Congo, from depths of 47–665 m. Adults mainly occur in fine silt and muddy sediments. Prionospio fallax Söderström, 1920 Fig. 8 Prionospio fallax Söderström, 1920: 235–237, figs 135, 144–145. Prionospio malmgreni – Eliason 1920: 51, fig. 13a–b. — Fauvel 1927: 61–62, fig. 21a–c. — Hannerz 1956: 40–46, figs 12–13. HEKTOEN M.M. et al., Partial revision of Northern European Prionospio (Annelida: Spionidae) 21 Prionospio fallax – Sigvaldadóttir & Mackie 1993: 207–211, figs 3–5. — Kirkegaard 1996: 82–83, fig. 37 — Hektoen et al. 2024: figs 1, 4. Diagnosis Prostomium anteriorly truncate, posteriorly extending to end of chaetiger 1 as a thick caruncle. Two pairs of dark red eyes (appear black when fixed in ethanol or formalin); median eyes small single spots to large patches; lateral eyes single spots. Four pairs of branchiae on chaetigers 2–5; branchiae of chaetigers 2 and 5 long, pinnate, with pinnules arranged in single lateral rows; branchiae of chaetigers 3 and 4 apinnate, similar in size to notopodial postchaetal lamellae. Dorsolateral longitudinal ciliation present between successive notopodia on chaetigers 4–7. High dorsal crest on chaetiger 7 only. Neuropodial postchaetal lamellae of chaetiger 2 elongated ventrally. Sabre chaetae in neuropodia from chaetiger 10. Hooded hooks in neuropodia from chaetigers 12–13. Type material Lectotype SWEDEN • Bohuslän, Lysekil, Islandsberg; 1891; A. Wirén leg.; designated by Sigvaldadóttir & Mackie (1993); UPSZTY 2255. Paralectotypes SWEDEN • 11 specs; Bohuslän, Lysekil, Islandsberg; 1891; A. Wirén leg.; designated by Sigvaldadóttir & Mackie (1993); UPSZTY 2255. Other material examined FRANCE • 14 specs; Banyuls-sur-Mer; 42°29.000′ N, 3°9.000′ E; depth 32 m; 1991; F. Pleijel leg.; Banyuls2; van Veen grab; SMNH 111902 • 9 specs; Banyuls-sur-Mer; 42°30.000′ N, 3°9.000′ E; depth 4 m; 1991; F. Pleijel leg.; van Veen grab; SMNH 111900 • 18 specs; Banyuls-sur-Mer; 42°30.102′ N, 3°9.288′ E; depth 40 m; 7 Oct. 1991; F. Pleijel leg.; stn Banyuls1991c; van Veen grab; SMNH 180570. ITALY • 17 specs; Siracusa, Brucoli; 37°16.300′ N, 15°11.500′ E; depth 60 m; 23 May 1990; F. Pleijel leg.; stn Sicily7; van Veen grab; SMNH 180568 • 10 specs; Catania; 37°35.500′ N, 15°11.800′ E; depth 140 m; 18 May 1990; F. Pleijel leg.; stn Acitrezza7; van Veen grab; SMNH 180567. NORWAY – Skagerrak • 8 specs; Oslofjorden; 28 Mar. 1952; van Veen grab; NHMO. – Østfold • 10 specs; Halden, Sponvika; 59°5.500′ N, 11°11.000′ E; depth 85 m; 23 Sep. 1992; stn Singlefjord 1992; van Veen grab; SMNH 111896 • 1 spec.; Halden, Sponvika; depth 25 m; 16 Sep. 1984; stn Sponvika2; van Veen grab; SMNH 111883. – Akershus • 1 spec.; Frogn, Drøbak; 59°38.682′ N, 10°37.302′ E; depth 10–45 m; 22 Oct. 2014; stn POLYSKAG 2014/10-18; van Veen grab; ZMBN 152633. – Vestfold • 1 spec.; Larvik; 59°2.667′ N, 10°1.537′ E; depth 43 m; 2020; NIVA leg.; stn lar-S27; van Veen grab; NTNU-VM 84043 • 4 specs; Holmestrand, Sande; 59°32.952′ N, 10°16.932′ E; depth 20–29 m; 30 May 2011; ZMBN leg; stn TR6; van Veen grab; ZMBN 152631 • 14 specs; 58°49.716′ N, 10°34.626′ E; depth 127–148 m; 17 May 2009; ZMBN leg.; stn BS48-82; sledge; ZMBN 152630. – Telemark • 1 spec.; Brevik, 59°3.620′ N, 9°41.891′ E; depth 10 m; 26 Aug. 2019; T. Bakken leg.; stn 2019091; van Veen grab; NTNU VM 77612. – Agder • 3 specs; Kristiansand, Skoltebukta; 58°7.503′ N, 7°58.788′ E; depth 31 m; 2020; NIVA leg.; stn K17; van Veen grab; NTNU-VM 84115 • 1 spec.; Tvedestrand, Sandvika; 58°34.080′ N, 9°1.860′ E; depth 22 m; 27 May 2011; NIVA leg.; stn GR3; van Veen grab; ZMBN 152616. – Vestland • 2 specs; Alver, Jibbersholmen; 60°45.052′ N, 4°53.330′ E; depth 80 m; 18 Dec. 2019; Åkerblå AS leg.; stn JIB-4; van Veen grab; NTNU-VM 84095 • 3 specs; Alver, Jibbersholmen; 60°45.169′ N, 4°53.273′ E; depth 115 m; 18 Dec. 2019; Åkerblå AS leg.; stn JIB-1; van Veen grab; NTNU-VM 84063 • 5 specs; Gulen, Hardbakkeneset; 61°1.035′ N, 4°56.645′ E; depth 110 m; 19 Sep. 2019; Åkerblå AS leg.; stn HAR-3; van Veen grab; NTNU-VM 84067 • 1 spec.; European Journal of Taxonomy 1027: 1–58 (2025) 22 Fjaler, Hegnes; 61°21.470′ N, 5°17.110′ E; depth 243 m; 4 Dec. 2019; Åkerblå AS leg.; stn HEG-1; van Veen grab; SEM stub; NTNU-VM 84157 • 1 spec.; same data as for preceding; SEM stub; NTNU-VM 84158 • 1 spec.; Fjaler, Hegnes; 61°21.579′ N, 5°17.270′ E; depth 244 m; 4 Dec. 2019; Åkerblå AS leg.; stn Heg-2; van Veen grab; NTNU-VM 84050 • 17 specs; same data as for preceding; NTNU-VM 84051 • 15+ specs; Bremanger Gulestø; 61°45.701′ N, 5°4.096′ E; depth 146 m; 8 Oct. 2019; Åkerblå AS leg.; stn GUL-3; van Veen grab; NTNU-VM 84059 • 11 specs; Bremanger Gulestø; 61°45.868′ N, 5°4.050′ E; depth 170 m; 8 Oct. 2019; Åkerblå AS leg.; stn GUL-2; van Veen grab; NTNU-VM 84057 • 10 specs; Sogndal, Beitveit; 62°8.171′ N, 5°19.906′ E; depth 138 m; 10 Oct. 2019; Åkerblå AS leg.; stn BEI-3; van Veen grab; NTNU-VM 84097 • 20 specs; Sogndal, Beitveit; 62°8.551′ N, 5°20.113′ E; 10 Oct. 2019; Åkerblå AS leg.; stn BEI-5; van Veen grab; NTNU-VM 84040 • 1 spec.; Bergen, Mortholmosen; 60°12.864′ N, 5°20.736′ E; depth 42–60 m; 9 Feb. 2006; ZMBN leg.; stn HB2006.02.09-2; sledge; ZMBN 152620 • 17 specs; Øygarden, Sund; 60°10.080′ N, 5°0.420′ E; depth 17 m; 23 Apr. 2014; ZMBN leg.; stn HB2014.04.24-3; van Veen grab; ZMBN 152627 • 1 spec.; Øygarden, Sund; 60°10.380′ N, 5°0.180′ E; depth 6 m; 23 Apr. 2014; ZMBN leg.; stn HB2014.04.24-4; van Veen grab; ZMBN 152626 • 50+ specs; Øygarden, Sund; 60°12.000′ N, 5°2.460′ E; depth 60 m; 23 Apr. 2014; ZMBN leg.; stn HB2014.04.24-5; van Veen grab; ZMBN 152623 • 35 specs; Øygarden, Sund; 60°12.046′ N, 5°2.305′ E; depth 30–60 m; 7 Sep. 2016; ZMBN leg.; stn HB2016.09.07-2; sledge; ZMBN 152621 • 7 specs; Bergen, Flesland; 60°17.052′ N, 5°12.087′ E; depth 72 m; 2 Sep. 2014; ZMBN leg.; stn HB2014.09.021; van Veen grab; ZMBN 152625 • 37 specs; Alver, Håøysundet; 60°32.984′ N, 5°13.738′ E; depth 37 m; 20 Apr. 2017; ZMBN leg.; stn HB2017.04.20-2; van Veen grab; ZMBN 152632 • 3 specs; Alver, Radfjorden; 60°36.009′ N, 5°9.262′ E; depth 106m; 6 Mar. 2017; ZMBN leg.; stn HB2017.03.06-5; van Veen grab; ZMBN 152624. – Møre og Romsdal • 10 specs; Rauma, Lybergsvika; 62°38.678′ N, 7°26.648′ E; depth 104 m; 18 Jul. 2019; Åkerblå AS leg.; stn LYB-5; van Veen grab; NTNU-VM 84058 • 5 specs; Rauma, Lybergsvika; 62°38.777′ N, 7°27.359′ E; depth 95 m; 18 Jul. 2019; Åkerblå AS leg.; stn LYB-6; van Veen grab; NTNU-VM 84056 • 1 spec.; Kristiansund, Or; 63°2.087′ N, 7°50.760′ E; depth 60 m; 13 Nov. 2019; Åkerblå AS leg.; stn OR-2; van Veen grab; NTNU-VM 84159 • 2 specs; same data as for preceding; NTNU-VM 84047 • 4 specs; Kristiansund, Or; 63°2.527′ N, 7°51.402′ E; depth 56 m; 13 Nov. 2019; Åkerblå AS leg.; stn OR-4; van Veen grab; NTNU-VM 84046 • 1 spec.; Smøla, Andholmane; 63°28.525′ N, 7°51.111′ E; depth 53 m; 17 Dec. 2019; Åkerblå AS leg.; stn AND-8; van Veen grab; NTNU-VM 84042 • 1 spec.; same data as for preceding; SEM stub; NTNU-VM 85853. – Trøndelag • 1 spec.; Trondheim, Grillstad; 63°26.340′ N, 10°30.329′ E; depth 3 m; 4 Sep. 2018; M. Capa et al. leg.; stn 2018033; van Veen grab; NTNU-VM 76719 • 1 spec.; Hitra, Reitholmen; 63°37.339′ N, 9°7.762′ E; depth 38 m; 27 Jan. 2022; Åkerblå AS leg.; stn REI-3; van Veen grab; NTNU-VM 84044 • 5 specs; Ørland, Havsund; 63°47.870′ N, 9°26.236′ E; depth 35 m; 30 Oct. 2019; Åkerblå AS leg.; stn HAV-5; van Veen grab; NTNU-VM 84055 • 1 spec.; Ørland, Havsund; 63°48.073′ N, 9°26.799′ E; depth 22 m; 30 Oct. 2019; Åkerblå AS leg; stn HAV-3; van Veen grab; NTNU-VM 84053 • 6 specs; Ørland, Havsund; 63°48.091′ N, 9°26.385′ E; depth 26 m; 30 Oct. 2019; Åkerblå AS leg.; stn HAV4; van Veen grab; NTNU-VM 84054. – Nordland • 1 spec.; Bodø, Brønnøyskjæran; 67°25.242′ N, 13°54.936′ E; depth 15 m; 25 Nov. 2021; Åkerblå AS leg.; stn BRØ-REF; van Veen grab; NTNUVM 84045. – Troms • 2 specs; Gratangen, Follesøy; 68°41.586′ N, 17°25.972′ E; depth 34 m; 28 Jan. 2022; Åkerblå AS leg.; stn FOL-2; van Veen grab; NTNU-VM 84065 • 4 specs; Hamarøy, Jøvik; 69°8.155′ N, 17°19.840′ E; depth 20 m; 21 Oct. 2020; Åkerblå AS leg.; stn JØV-1; van Veen grab; NTNU-VM 84060 • 1 spec.; Hamarøy, Hallarøy; 69°8.820′ N, 16°51.778′ E; depth 97 m; 29 Oct. 2019; Åkerblå AS leg.; stn HAL-REF; van Veen grab; NTNU-VM 84061 • 1 spec.; Tromsø; 69°46.362′ N 19°13.869′ E; 29 Mar. 2021; Åkerblå AS leg.; stn R1-4; van Veen grab; NTNU-VM 84052 • 2 specs; Karlsøy, Dåvøy; 70°3.313′ N, 19°18.781′ E; depth 72 m; 11 Nov. 2021; Åkerblå AS leg; stn DÅV-REF; van Veen grab; NTNU-VM 84069 • 5 specs; Karlsøy, Karaneset; 70°3.586′ N, 19°18.296′ E; depth 63 m; 11 Aug. 2021; Åkerblå AS leg.; stn KAR-2; van Veen grab; NTNU-VM 84070 • 9 specs; Karlsøy, Karaneset; 70°3.734′ N, 19°18.379′ E; depth 97 m; 11 Aug. 2021; Åkerblå AS leg.; stn KAR-3; van Veen grab; NTNU-VM 84071 • 1 spec.; Karlsøy Karaneset; 70°4.132′ N, 19°18.715′ E; depth 73 m; 11 Aug. HEKTOEN M.M. et al., Partial revision of Northern European Prionospio (Annelida: Spionidae) 23 2021; Åkerblå AS leg.; stn KAR-4; van Veen grab; NTNU-VM 84064 • 2 specs; Karlsøy, Karaneset; 70°6.109′ N, 19°35.191′ E; depth 134 m; 11 Aug. 2021; Åkerblå AS leg.; stn KAR-5; van Veen grab; NTNU-VM 84073 • 5 specs; Karlsøy, Nordnibba; 70°9.855′ N, 19°21.322′ E; depth 73 m; 11 Oct. 2021; Åkerblå AS leg.; stn NOR-REF; van Veen grab; NTNU-VM 84038 • 1 spec.; Karlsøy, Nordnibba; 70°9.993′ N, 19°22.469′ E; depth 67 m; 11 Oct. 2021; Åkerblå AS leg.; stn NOR-5; van Veen grab; NTNU-VM 84039. SWEDEN • 1 spec.; depth 10–20 m; 1991; stn Krugglö91; sledge; SMNH 111893. – Halland • 7 specs; Varberg, Värö; 57°10.000′ N, 12°1.000′ E; depth 47 m; 1984; stn VÄRV84#3; van Veen grab; SMNH 53678 • 88 specs; Varberg, Värö; 57°10.000′ N, 12°5.000′ E; depth 20 m; 1980; stn Varö spring 1980 2; van Veen grab; SMNH 9554 • 50 specs; Varberg, Värö; 57°10.000′ N, 12°1.000′ E; depth 47 m; 1978; stn Varö spring 1980 3; van Veen grab; SMNH 6453 • 30 specs; Varberg Värö; 57°10.000′ N, 12°5.000′ E; depth 20 m; 1984; stn VÄRH84#2; van Veen grab; SMNH 52794 • 100 specs; Varberg, Värö; 57°10.000′ N, 12°1.000′ E; depth 47 m; 1979; stn VÄRV79#3; van Veen grab; SMNH 8710 • 20 specs; Varberg, Värö; 57°13.000′ N, 12°1.000′ E; depth 39 m; 1984; stn VÄRH84#4; van Veen grab; SMNH 53565 • 20 specs; Varberg, Värö; 57°13.000′ N, 12°4.000′ E; depth 21 m; 1987; stn VÄRV87#1; van Veen grab; SMNH, 54728 • 50 specs; Varberg, Värö; 57°13.000′ N, 12°4.000′ E; depth 21 m; 1984; stn VÄRH84#1; van Veen grab; SMNH 52763 • 13 specs; Varberg, Värö; 57°16.000′ N, 12°5.000′ E; depth 19 m; 1981; stn VÄRH81#7; van Veen grab; SMNH, 11431 • 150 specs; Varberg, Värö; 57°16.000′ N, 12°5.000′ E; depth 19 m; 1984; stn VÄRV84#7; van Veen grab; SMNH 53617. UNITED KINGDOM • 10 specs; Loch Creran; 56.523511 N, 5.355115 W; depth 25 m; 31 May 1905; stn Loch Creran4; van Veen grab; SMNH 180569. Examined material with sequence data NORWAY – Akershus • 2 specs; Asker, Sætre; 59°39.372′ N, 10°36.486′ E; depth 18–45 m; 20 Oct. 2014; stn POLYSKAG 2014/10-3; van Veen grab; ZMBN 152617. – Oslo • 1 spec.; Oslo; 59°54.434′ N, 10°44.013′ E; depth 13 m; 18 Sep. 2018; M. Capa leg; stn 2018188; van Veen grab; NTNU-VM 76527. – Vestfold • 1 spec.; 58°49.716′ N, 10°34.626′ E; depth 127–148 m; 17 May 2009; ZMBN leg.; stn BS48-82; sledge; ZMBN 152618. – Agder • 1 spec.; Kristiansand, Skoltebukta; 58°9.026′ N, 8°2.060′ E; depth 8 m; 23 Aug. 2019; T. Bakken leg.; etsn. 2019060; van Veen grab; NTNU-VM 77485. Fig. 8. Adult morphology of Prionospio fallax Söderström, 1920. SEM micrographs. A. Anterior end, left dorsolateral view (NTNU-VM 85853). B. Anterior end, left ventro-lateral view (NTNU-VM 84159). Abbreviations: see Material and methods. Scale bars = 100 μm. European Journal of Taxonomy 1027: 1–58 (2025) 24 – Vestland • 12 specs; Bergen, Bergsvika; 60°19.133′ N, 5°15.317′ E; depth 48 m; 12 Sep. 2019; M. Capa leg.; stn SØR D1; van Veen grab; NTNU-VM 76741 • 1 spec.; Alver, Jibbersholmen; 60°45.052′ N, 4°53.330′ E; depth 80 m; 18 Dec. 2019; Åkerblå AS leg.; stn JIB-4; van Veen grab; NTNU-VM 84096 • 1 spec.; Fjaler, Hegnes; 61°21.470′ N, 5°17.110′ E; depth 243 m; 4 Dec. 2019; Åkerblå AS leg.; stn HEG-1; van Veen grab; NTNU-VM 84049 • 1 spec.; Sogndal, Beitveit; 62°8.171′ N, 5°19.906′ E; depth 138 m; 10 Oct. 2019; Åkerblå AS leg.; stn BEI-3; van Veen grab; NTNU-VM 84098 • 1 spec.; Øygarden, Fjell; 60°19.591′ N, 5°8.451′ E; depth 75 m; 2 Sep. 2014; ZMBN leg.; stn HB2014.09.022; van Veen grab; ZMBN 152629 • 1 spec.; Øygarden, Sund; 60°10.080′ N, 5°0.420′ E; depth 17 m; 23 Apr. 2014; ZMBN leg.; stn HB2014.04.24-3; van Veen grab; ZMBN 152615 • 1 spec.; Øygarden, Sund; 60°12.046′ N, 5°2.305′ E; depth 30–60 m; 7 Sep. 2016; ZMBN leg.; stn HB2016.09.07-2; sledge; ZMBN 152628 • 1 spec.; Bergen, Flesland; 60°17.052′ N, 5°12.087′ E; depth 72 m; 2 Sep. 2014; ZMBN leg.; stn HB2014.09.02-1; van Veen grab; ZMBN 152619 • 1 spec.; Alver, Håøysundet; 60°32.984′ N, 5°13.738′ E; depth 37 m; 20 Apr. 2017; ZMBN leg.; stn HB2017.04.20-2; van Veen grab; ZMBN 152622 • 1 spec.; Alver, Radfjorden; 60°36.009′ N, 5°9.262′ E; depth 106m; 6 Mar. 2017; ZMBN leg.; stn HB2017.03.06-5; van Veen grab; ZMBN 152634. – Møre og Romsdal • 1 spec.; Kristiansund, Or; 63°2.087′ N, 7°50.760′ E; depth 60 m; 13 Nov. 2019; Åkerblå AS leg.; stn OR-2; van Veen grab; NTNUVM 84048. – Trøndelag • 1 spec.; Trondheim; 63°26.308′ N, 10°23.940′ E; depth 6 m; 5 Sep. 2018; M. Capa et al. leg.; stn 2018044; van Veen grab; NTNU-VM 75547. Remarks The new material agrees well with the type specimens and original and later descriptions of P. fallax (Söderström 1920; Sigvaldadóttir & Mackie 1993). Among Northeast Atlantic species of Prionospio, P. fallax is uniquely distinguished by the presence of a prominent single dorsal crest on chaetiger 7. Although the type material was made available for examination at UPSZTY, the microscopy facilities on site were inadequate for detailed morphological study or for obtaining diagnostic photographs. Additionally, the types were not available for loan. Due to these limitations, we did not attempt a full redescription or imaging of the type material. Some morphological features not previously described for P. fallax were observed in the present study in the non-type material. Some large individuals had pinnules present almost to the tip of branchiae (Fig. 8A), rather than absent on long distal part of branchiae (Fig. 8B), as described by Söderström (1920) and Sigvaldadóttir & Mackie (1993). Large specimens had notopodial postchaetal lamellae of chaetiger 6 and / or chaetiger 8 basally extending halfway across the dorsum; however, these extensions never met middorsally to form transverse crests (Fig. 8A). Dorsolateral longitudinal ciliation between chaetigers 4–7 is documented here for P. fallax for the first time. Prionospio fallax has been reported from Norway, Sweden, Scotland, and the Mediterranean Sea (Sigvaldadóttir & Mackie 1993). We found no morphological differences between populations from northern Europe and the Mediterranean. However, it should be noted that molecular data are currently only available for specimens from Norwegian waters. Broader sampling and genetic analysis might be needed to confirm the identity of the Mediterranean populations. Habitats and distribution Prionospio fallax is known from Norway, Sweden, Scotland and the western Mediterranean Sea between 4 and 244 m depth. Prionospio sanmartini Delgado-Blas, Díaz-Díaz & Viéitez, 2019 Figs 9–11 Prionospio (Minuspio) sanmartini Delgado-Blas, Díaz-Díaz & Viéitez, 2019: 568–573, fig. 3, table 1. HEKTOEN M.M. et al., Partial revision of Northern European Prionospio (Annelida: Spionidae) 25 Prionospio (Minuspio) multibranchiata – Mackie 1984: 40–42, fig. 3, table 2. Prionospio multibranchiata – Kirkegaard 1996: 84–85, fig. 38. Prionospio (Minuspio) cirrifera – Hartmann-Schröder 1996: 329–330 (partim). Prionospio cf. sanmartini – Hektoen et al. 2024: figs 1, 4. Diagnosis Prostomium narrow, anteriorly rounded, posteriorly extending to middle of chaetiger 2 as a narrow caruncle. Two pairs of eyes present; median eyes single or multiple spots sometimes fused together. Eight to 13 pairs of apinnate branchiae from chaetiger 2. Low dorsal crests from chaetigers 12–14. Neuropodial postchaetal lamellae of chaetiger 2 not elongated ventrally. Sabre chaetae in neuropodia from chaetigers 12–17. Hooded hooks in notopodia from chaetigers 35–41, in neuropodia from chaetigers 13–19. Type material Paratypes SPAIN • 9 specs; Galicia, Ría de Foz; 43°33′ N, 7°15′ W; J. Junoy leg.; stn CC1. XII.85; MNCN 16.01/18448. Other material examined FRANCE • 20 specs; Banyuls sur Mer; 42°30.000′ N, 3°9.000′ E; depth 4 m; F. Pleijel leg.; stn Banyuls1; van Veen grab; SMNH 111901 • 3 specs; Banyuls sur Mer; 42°29.000′ N, 3°9.000′ E; depth 32 m; F. Pleijel leg.; stn Banyuls2; van Veen grab; SMNH 111903. ITALY • 11 specs; Sicily, Brucoli; 37°17.000′ N, 15°11.000′ E; depth 40 m; 1990; Mission Sicile Orientale 1990 leg.; stn Sicily1 1990; van Veen grab; SMNH 111895. NORWAY – Vestfold • 3 specs; Larvik, Larviksfjorden; 59°2.667′ N, 10°1.537′ E; depth 43 m; 2020; NIVA leg.; stn LAR-S27; van Veen grab; NTNU-VM 84121 • 1 spec.; Sandefjord; 59°0.786′ N, 10°22.301′ E; depth 57 m; 2019; NIVA leg.; stn A05/BT40; van Veen grab; NTNU-VM 84118 • 8 specs; Larvik, Stavern; 58°59.815′ N, 10°2.710′ E; depth 13 m; 2020; NIVA leg.; stn STA-1; van Veen grab; NTNU-VM 84119. – Telemark • 7 specs; Porsgrunn; 59°3.220′ N, 9°45.069′ E; depth 31 m; 2018; NIVA leg.; stn F04-C; van Veen grab; NTNU-VM 84122. – Agder • 6 specs; Kristiansand, Skoltebukta; 58°7.503′ N, 7°58.788′ E; depth 31 m; 2020; NIVA leg.; stn K17; van Veen grab; NTNU-VM 84116 • 18 specs; Kristiansand, Skoltebukta; 58°7.465′ N, 7°58.472′ E; depth 20 m; 2020; NIVA leg.; stn EC1; van Veen grab; NTNU-VM 84117 • 3 specs; Kristiansand, Skoltebukta; 58°7.161′ N, 7°58.661′ E; depth 17 m; 2020; NIVA leg.; stn KH03; van Veen grab; NTNU-VM. 84120. SWEDEN – Bohuslän • 1 spec.; Strömstad, Tjärnö; 58°52.860′ N, 11°6.480′ E; 2019; A. Nygren leg.; stn KAU-02; van Veen grab; NTNU-VM 84124 • 5 specs; Tanum, Väderöarna; depth 118 m; 1985; stn Väderöarna2; van Veen grab; SMNH 111879 • 4 specs; Tanum, Väderöarna; depth 40 m; 1984; van Veen grab; SMNH 111880. – Halland • 2; Varberg, Värö; 57°10.000′ N, 12°5.000′ E; depth 20 m; 1978; stn VÄRV78#2; van Veen grab; SMNH 6442 • 50 specs; Varberg, Värö; 57°10.000′ N, 12°1.000′ E; depth 47 m; 1978; stn VÄRV78#3; van Veen grab; SMNH 6452 • 100 specs; Varberg, Värö; 57°10.000′ N, 12°1.000′ E; depth 47 m; 1979; stn VÄRV79#3; van Veen grab; SMNH 8706 • 50 specs.; Varberg, Värö; 57°10.000′ N, 12°1.000′ E; depth 47 m; 1980; stn VÄRV80#3; van Veen grab; SMNH 9630 • 50 specs; Varberg, Värö; 57°16.000′ N, 12°5.000′ E; depth 19 m; 1980; stn VÄRV80#7; van Veen grab; SMNH 10104 • 2 specs; Varberg, Värö; 57°13.000′ N, 12°4.000′ E; depth 21 m; 1984; stn VÄRH84#1; van Veen grab; SMNH 52762 • 4 specs; Varberg, Värö; 57°16.000′ N, 12°5.000′ E; depth 19 m; 1984; stn VÄRV84#7; van Veen grab; SMNH 53618 • 12 specs; Varberg, Värö; 57°10.000′ N, 12°1.000′ E; depth 47 m; 1984; stn VÄRV84#3; van Veen grab; SMNH 53677 • 5 specs; Varberg, Värö; 57°13.000′ N, 12°1.000′ E; depth 39 m; 1984; stn VÄRH84#4; van Veen grab; SMNH 53565 • 5 specs; Varberg, Värö; European Journal of Taxonomy 1027: 1–58 (2025) 32 ventrally (Fig. 14B), subrectangular on chaetigers 3 and 4 (Fig. 14C–D), from chaetiger 5 evenly rounded (Fig. 14E–I), from chaetiger 13 low and oval. Notopodial capillaries on anterior and middle chaetigers arranged in two rows, unilimbate and granulated. Neuropodial capillaries arranged in two rows in anterior chaetigers, unilimbate and granulated; anterior row shorter than posterior row in both rami. Chaetae on posterior chaetigers not observed. Sabre chaetae in neuropodia from chaetigers 16–17 (chaetiger 17 in holotype), up to two per fascicle, with granulation on distal part of shaft (Fig. 14K). Hooded hooks in notopodia present only in holotype, from chaetiger 34 onwards (other specimens are shorter anterior fragments). Hooded hooks first appearing in neuropodia from chaetigers 17–18 (chaetiger 18 in holotype), alternating with capillary chaetae. Neuropodial hooded hooks usually appear in next chaetiger after the first sabre chaetae, up to eight in series. Both notoand neuropodial hooks with 4–5 pairs of small upper teeth arranged in two vertical rows above main fang (Fig. 14J), with outer and a small inner hoods. Fig. 13. Adult morphology of Prionospiofiordicasp. nov. Anterior ends stained with methylene green. A. Paratype (NTNU-VM 84110 ), dorsal view. B. Paratype (NTNU-VM 84114), left lateral view. Abbreviations: see Material and methods. Scale bars = 200 μm. HEKTOEN M.M. et al., Partial revision of Northern European Prionospio (Annelida: Spionidae) 33 Pygidium missing in all specimens. Remarks Fixed specimens of Prionospiofiordicasp. nov. are fragile, making detailed study challenging. All specimens were anterior fragments, often damaged, lacking notopodial postchaetal lamellae and branchiae. Only the holotype had more than 30 chaetigers and was the only specimen with hooded hooks in notopodia. The species was sequenced by Hektoen et al. (2024) and was found to be genetically different from all other species studied. Prionospiofiordica sp. nov. can be distinguished from P. multibranchiata (based on the redescription by Delgado-Blas et al. 2018) primarily by the dorsal crests (present in P.fiordica sp. nov. and absent in P. multibranchiata). Other differences include the shape of the eyes (small and represented by single eyespots in the former and large and conspicuous in the latter). It can be distinguished from P. maciolekae (based on the description by Dagli & Çinar, 2011) by the shape of prostomium (triangular, anteriorly truncate in P.fiordica and subrectangular, anteriorly rounded in P. maciolekae), the shape of the neuropodial postchaetal lamellae of chaetiger 3 (broadly rounded in the former and narrowly rounded, becoming finger-like in the latter). Prionospio fiordica sp. nov. can be distinguished from P. sanmartini primarily by the shape of prostomium (triangular and truncate anteriorly with a short thick caruncle in the former, and anteriorly Fig. 14. Morphology of parapodia and chaetae of Prionospiofiordicasp. nov. (ZMBN 152606). A–I. Chaetigers 1–5, 7, 9, 11, 12. J. Hooded hook from neuropodium of chaetiger 15. K. Sabre chaeta from neuropodium of chaetiger 20. Abbreviations: see Material and methods. Scale bars: A–I = 100 μm; J–K = 10 μm. European Journal of Taxonomy 1027: 1–58 (2025) 34 rounded, widest just before the lateral eyes, with a narrow caruncle in the latter), and the shape of the peristomium (more developed in P.fiordica). Other differences include the shape of eyes (always indistinct small single spots in the former, and larger in the latter), and sabre chaetae and hooded hooks in neuropodia, generally starting later in P.fiordica(from chaetigers 16–17 and 17–18, respectively) than in P. sanmartini (from chaetigers 12–17 and 13–18). Prionospiofiordicasp. nov. was referred in the molecular study by Hektoen et. al. (2024) as Prionospio sp. 3. The species is genetically distinct from multibranchiate Prionospio from Skagerrak and southern Europe (Prionospio cf. sanmartini in Hektoen et al. 2024, assigned here to P. sanmartini), and from the Eastern and Western Pacific (referred in Hektoen et al. 2024 as P. multibranchiata). Based on the current data, there seems to be a geographic and bathymetric separation between P.fiordicaand P. sanmartini, where P. sanmartini has not yet been recorded from Western Norway, and not deeper than 118 m, while P.fiordicahas exclusively been found in fjords and offshore western Norway deeper than 328 m. Habitats and distribution Adults ofP.fiordicasp. nov. were collected from the northern part of the North Sea and southern part of the Norwegian Sea, both offshore and in fjords in Vestland and Møre og Romsdal counties of Norway. They were found in fine silt and muddy sediments at depts of 328–1236 m. The conspecificity of individuals from such a wide bathymetric range was confirmed with molecular analysis by Hektoen et al. (2024). Prionospio plumosa M. Sars in G.O. Sars, 1872 Figs 15–17 Prionospio plumosus M. Sars in G.O. Sars, 1872: 410–411. Prionospio (Prionospio) tripinnata Maciolek, 1985: 343–345, fig. 6. Syn. nov. Prionospio plumosus – Sars 1873: 263–268, figs 13–29. — Bidenkap 1894: 94. Prionospio steenstrupi – Bidenkap 1894: 93. Prionospio plumosa – Söderström 1920: 233–234, fig. 141. — Kirkegaard 1996: 86, fig. 39. — Hektoen et al. 2024: figs 1, 4. Prionospio (Prionospio) plumosa – Hartmann-Schröder 1996: 326–327. Prionospio sp. – Gaudron et al. 2010: 5 (genetic data). — Rubin-Blum et al. 2014 (genetic data). Diagnosis Prostomium triangular, anteriorly truncate, posteriorly extending to end of chaetiger 1 as a short caruncle. Eyes absent in adults. Four pairs of branchiae on chaetigers 2–5; those of chaetigers 2, 3 and 5 with digitiform pinnules, branchiae of chaetiger 4 apinnate. Branchiae of chaetigers 2 and 5 long, with naked distal tips, on chaetigers 3 and 4 short and stout. Neuropodial postchaetal lamellae of chaetiger 2 not elongated ventrally. Dorsal crests from chaetiger 6 or 7. Sabre chaetae in neuropodia from chaetigers 10– 12, with heavily granulated distal part. Hooded hooks in notopodia from chaetigers 26–43, in neuropodia from chaetigers 12–14. Type material of Prionospio plumosa Neotype (designated here) NORWAY • Filtvedt, Brændtangen, Drøbaksundet; 18 Aug. 1910; Hvitfisken Kristianiafjorden leg.; van Veen grab; NHMO C7075. HEKTOEN M.M. et al., Partial revision of Northern European Prionospio (Annelida: Spionidae) 35 Type material of Prionospio tripinnata Holotype LIBYA • 33°57.000′ N, 15°8.202′ E; depth 500–509 m; 2 Sep. 1970; Atlantis II R/V 59 leg.; stn 211; USNM 67678. Other material examined SWEDEN – Bohuslän • 5 specs; Väderön; depth 109 m; 29 Jun. 1869; stn VädOls6; SMNH 120288. NORWAY – Rogaland • 1 spec.; Sauda; depth 38 m; 6 May 1981; stn7; NTNU-VM 25670 • 10 specs; Bokn, Lådeskjera; 59°11.893′ N, 5°28.880′ E; depth 102 m; 4 Apr. 2021; Åkerblå AS leg.; stn LÅD-1; van Veen grab; NTNU-VM 84075. – Vestland • 2 specs.; Ullensvang, Hessvik; 0°07.754′ N, 6°09.062′ E; depth 66 m; 1 Jul. 2010; SAM leg.; stn HES 1-1; van Veen grab; SMNH 129904 • 1 spec.; Bergen, Lyreneset; 60°23.692′ N, 5°16.214′ E; depth 34 m; 6 Jun. 1999; SAM leg.; stn Lyr2-1, van Veen grab; SMNH 129905 • 20 specs; Gulen, Hardbakkeneset; 61°01.003′ N, 4°57.039′ E; depth 80 m; 19 Sep. 2019; Åkerblå AS leg.; stn HAR-1; van Veen grab; NTNU-VM 84082 • 15 specs; Fjaler, Hegnes; 61°21.470′ N, 5°17.110′ E; depth 244 m; 4 Dec. 2019; Åkerblå AS leg.; stn HEG-1; van Veen grab; NTNU-VM 84079 • 2 specs; Flora, Vågsøya; 61°29.177′ N, 5°01.489′ E; depth 71 m; 31 Oct. 2019; Åkerblå AS leg.; stn VÅG-1; van Veen grab; NTNU-VM 84080 • 30 specs; Bremanger Gulestø; 61°45.515′ N, 5°04.437′ E; depth 145 m; 8 Oct. 2019; Åkerblå AS leg.; stn GUL-1; van Veen grab; NTNU-VM 84078 • 2 specs; same data as for preceding; SEM stub; NTNU-VM 85856 • 1 spec.; same data as for preceding; SEM stub; NTNU-VM 85855 • 2 specs; Selje, Beitveit; 62°08.325′ N, 5°19.764′ E; depth 117 m; 10 Oct. 2019; Åkerblå AS leg.; stn BEI-1; van Veen grab; NTNU-VM 84091 • 20 specs; Alver, Jibbersholman; 60°45.052′ N, 4°53.330′ E; depth 80 m; 18 Dec. 2019; Åkerblå AS leg; stn JIB-4; van Veen grab; NTNU-VM 84076 • 5 specs; Gulen, Lyngholmen; 61°00.924′ N, 5°00.550′ E; depth 112 m; 20 Apr. 2021; Åkerblå AS leg.; stn LYN-1; van Veen grab; NTNU-VM 84084 • 10 specs; Fjaler, Kyravika; 61°19.115′ N, 5°09.559′ E; depth 400 m; 14 Dec. 2021; Åkerblå AS leg.; stn KYR-1; van Veen grab; NTNU-VM 84081 • 20 specs; Bremanger, Juvika B; 61°53.805′ N, 5°38.062′ E; depth 186 m; 9 Dec. 2021; Åkerblå AS leg.; stn JUV-1; van Veen grab; NTNU-VM 84088 • 2 specs; Bergen, Brettesnes; depth 36–55 m; M. Sars leg.; van Veen grab; NHMO C7022. – Møre og Romsdal • 25 specs; Stranda, Opshaugvik; 62°17.350′ N, 6°59.630′ E; depth 376 m; 31 Mar. 2020; Åkerblå AS leg.; stn OPS-3; van Veen grab; NTNU-VM 84093 • 17 specs; Fræna, Storvika; 62°48.113′ N, 6°58.539′ E; depth 182 m; 24 Sep. 2019; Åkerblå AS leg.; stn STO-1; van Veen grab; NTNU-VM 84074 • 1 spec.; Gjemnes, Høybuvika; 62°57.443′ N, 8°03.334′ E; depth 285 m; 14 Dec. 2021; Åkerblå AS leg.; stn HØY-3; van Veen grab; NTNU-VM 84077 • 20 specs; Høybuvika; 62°57.545′ N, 8°03.082′ E; depth 281 m; 14 Dec. 2021; Åkerblå AS leg.; stn HØY-1; van Veen grab; NTNU-VM 84086 • 15+ specs; Ørsta, Sagelva; 62°20.277′ N, 6°23.084′ E; depth 186 m; 7 Oct. 2020; Åkerblå AS leg.; stn SAG-1; van Veen grab; NTNU-VM 84085 • 1 spec.; same data as for preceding; SEM stub; NTNU-VM 85857 • 1 spec.; same data as for preceding; SEM stub; NTNU-VM 85858 • 10 specs; Kristiansund, Endreset; 63°01.893′ N, 7°42.726′ E; depth 203 m; 10 Sep. 2019; Åkerblå AS leg.; stn END-4; van Veen grab; NTNU-VM 84087. – Trøndelag • 5+ specs; Heim, Vullum; 63°02.888′ N, 8°12.819′ E; depth 282 m; 3 Aug. 2021; Åkerblå AS leg.; stn VUL-1; van Veen grab; NTNU-VM 84090 • 13 specs; Fiborgtangen; 63.7165° N, 11.1457°; depth 30 m; 1983; stn 13; van Veen grab; NTNU-VM 25391 • 3 specs; same data as for preceding; NTNU-VM 25389 • 5 specs; same data as for preceding; NTNU-VM 25390 • 1 spec.; Ørland, Storforsna, Vågen; 63.6541° N, 9.4069° E; depth 80–120 m; 1951; E. Sivertsen leg.; NTNU-VM 25797. – Troms • 5 specs; Tromsø, Tromsø; depth 273 m; 30 Jun. 2010; van Veen grab; SMNH 129903. Examined material with sequence data NORWAY – Vestland • 1 spec.; Fjaler, Hegnes; 61°21.470′ N, 5°17.110′ E; depth 244 m; 4 Dec. 2019; Åkerblå AS leg.; stn HEG-1; van Veen grab; NTNU-VM 84089 • 1 spec.; Selje, Beitveit; 62°08.325′ N, European Journal of Taxonomy 1027: 1–58 (2025) 36 5°19.764′ E; depth 117 m; 10 Oct. 2019; Åkerblå AS leg.; stn BEI-1; van Veen grab; NTNU-VM 84092 • 1 spec.; Alver, Jibbersholman; 60°45.052′ N, 4°53.330′ E; depth 80 m; 18 Dec. 2019; Åkerblå AS leg.; stn JIB-4; van Veen grab; NTNU-VM 84094 • 1 spec.; Bergen, Flesland; 60°17.052′ N, 5°12.087′ E; depth 72 m; 2 Sep. 2014; Bergen University Museum leg.; stn HB2014.09.02-1; van Veen grab; ZMBN 152635. – Nordland • 1 spec.; Alstahaug, Skorpa; 66°01.900′ N, 12°28.864′ E; depth 107 m; 22 Nov. 2019; Åkerblå AS leg.; stn NSK-1; van Veen grab; NTNU-VM 84083. Description (adults) Neotype (NHMO C7075) anterior fragment, 18 mm long, 1.7 mm wide, with 30 chaetigers, too damaged for close morphological examination after chaetiger 20. Color in alcohol pale brown to white. Prostomium triangular, anteriorly truncate, posteriorly extending to end of chaetiger 1 as a short, narrow caruncle. Nuchal organs U-shaped ciliary bands lateral to caruncle (Fig. 15A). Neotype without eyes, some small specimens with faint lateral eyespots (NTNU-VM 84077, 84085; Fig. 15B–C). Posterior dorsolateral parts of peristomium fused with notopodial postchaetal lamellae of chaetiger 1, forming ear-shaped structures lateral to prostomium. Palps missing in all specimens. Branchiae on chaetigers 2–5; those of chaetigers 2, 3 and 5 with digitiform pinnules on anterior sides; branchiae of chaetiger 4 apinnate. Branchiae of chaetigers 2 and 5 long, rounded in cross section, those of chaetigers 3 and 4 shorter, triangular in cross section (Fig. 15A) with dense lateral ciliation, distally flattened, foliaceous (Figs 15C–D, 16C–D). Branchiae of chaetiger 2 with apinnate basal part, densely pinnate on anterior side three-fourths up the branchiae, ending in apinnate tip (Fig. 16B). Branchiae of chaetiger 3 sparsely pinnate on anterior side halfway to two-thirds up branchiae (Fig. 16C). Branchiae of chaetiger 4 apinnate, with raised edge running up the branchia (Figs 15A, 16D); branchiae of chaetiger 5 densely pinnate on anterior side along almost entire length, with short slender apinnate tip (Fig. 16E). Nototrochs transverse ciliary bands between branchial bases on chaetigers 2–5. Dorsolateral longitudinal ciliation present between chaetigers 4–6. Notopodial prechaetal lamellae small, rounded on anterior chaetigers, reduced in posterior chaetigers. Notopodial postchaetal lamellae of chaetiger 1 triangular (Figs 16A, 17A), fused with peristomium, on chaetigers 2–5 large and subtriangular, largest on chaetiger 3 (Figs 16B–E, 17A). Lamellae rapidly diminishing in size, lower and rounded in postbranchial chaetigers, assuming low oval shape from chaetigers 8–9 (Fig. 16F–H). Notopodial postchaetal lamellae joined across dorsum forming transverse crests from chaetiger 6 to chaetigers 10–15, crest highest on chaetiger 7 (Figs 15A, C–D, 16F–H). Crest not visible at all on chaetiger 6 in some smaller specimens. Neuropodial prechaetal lamellae inconspicuous. Neuropodial postchaetal lamellae of chaetiger 1 broadly rounded, about one third to half the size of lamellae on subsequent chaetigers (Figs 16A, 17A); lamellae of chaetiger 2 subrectangular, higher than broad with rounded edges (Figs 16B, 17A); lamellae of chaetiger 3 oval, broad (Figs 16C, 17A); lamellae of chaetiger 4 quadrangular with rounded edges (Figs 16D, 17A); lamellae of subsequent chaetigers rounded, low and oval by chaetiger 12 (Fig. 16E–H), reduced on succeeding chaetigers. Interneuropodial pouches absent. Notopodial capillaries on anterior chaetigers arranged in numerous rows (7+), unilimbate and slightly granulated. Notopodial capillaries on middle chaetigers in two rows, unilimbate and slightly granulated. Neuropodial capillaries arranged in two rows in anterior chaetigers, unilimbate, granulated, anterior row shorter than posterior row. Posterior chaetae not observed in neotype, but notopodial capillaries in posterior chaetigers long, thin, alimbate and granulated in other specimens (NTNU-VM 85856). Sabre chaetae in neuropodia from chaetigers 10–12 (chaetiger 10 in neotype) with strong granulation on median and distal parts of shaft, up to 10 per fascicle in neotype, up to three in smaller specimens (Fig. 17B). Hooded hooks in notopodia not present in neotype, from chaetigers 26–47 in other specimens (NTNUVM 84090), up to six per ramus. Hooded hooks in neuropodia from chaetiger 12–14 (14 in neotype), up HEKTOEN M.M. et al., Partial revision of Northern European Prionospio (Annelida: Spionidae) 37 Fig. 15. Adult morphology of Prionospio plumosa M. Sars in G.O. Sars, 1872. A, D. SEM micrographs. B–C. Light microscope images. A–D. Anterior ends, dorsal view. A. NTNU-VM 85856. B. NTNU-VM 84085 (arrow pointing to small red eye). C. Neotype (NHMO C7075) stained with methylene green. D. NTNU-VM 84085. Abbreviations: see Material and method. Scale bars: A–B, D = 200 μm; C = 500 μm. European Journal of Taxonomy 1027: 1–58 (2025) 38 to eight per ramus. Both notopodial and neuropodial hooks with 3–4 pairs of upper teeth arranged in two vertical tows above main fang, with only outer hood, secondary inner hood absent (Fig. 17C). Pygidium with one long middorsal cirrus and one pair of short ventral cirri (NTNU-VM 84084, 84086, 84093), missing in neotype. Remarks A brief original description of Prionospio plumosus by Michael Sars was published after his death (22 October 1869) by his son, a Norwegian marine and freshwater biologist and professional illustrator Georg Ossian Sars (1872). The original description was based on an unknown number of specimens from the Drøbak sound, southern Norway. Later, Sars (1873) provided a detailed description and illustrations of this species. The type material was likely originally stored in the Natural History Museum, Oslo, but was not located by us or the curator of the NHMO (Ann-Helén Rønning pers. Fig. 16. Morphology of anteriorly facing parapodia of Prionospio plumosa M. Sars in G.O. Sars, 1872 (NTNU-VM 84088). A–G. Chaetigers 1–7. H. Chaetiger 10. Abbreviations: see Material and methods. Scale bars = 200 μm. HEKTOEN M.M. et al., Partial revision of Northern European Prionospio (Annelida: Spionidae) 39 comm.). Sigvaldadóttir (1998) listed the type material of P. plumosa as deposited in the polychaete collection of the Smithsonian Institution, Washington D.C. (USNM 32698). However, neither the authors or curators were able to locate this material in the museum and the noted catalogue number is currently assigned to the holotype of Prionospio ornata Berkeley & Berkeley, 1961 from Peru (http://n2t.net/ark:/65665/308a8bc18-4af6-4154-8d3b-e822fb633267). Therefore, we consider the types of P. plumosa to be lost. To ensure nomenclatural stability, we designate here a neotype (NHMO C7075). The specimen was collected in 1910 between Filtvet and Brenntangen in the Oslofjord, which is a narrow stretch of approximately 1.5 km long and depth up to 200 m. No further information is given on the label. The noted location is about 10 km south of the original type locality at Drøbak (Sars 1872; Oug et al. 2014). Prionospio plumosa is rare, if still occurring, in the Oslofjord. The species has not been reported in the region in over a century, despite targeted sampling of Sars’ type localities in the past decade (Oug et al. 2015). Prionospio tripinnata Maciolek, 1985 was described based on a single specimen from a depth of 500 m in the Mediterranean Sea (Maciolek 1985). The species was differentiated from P. plumosa by the branchiae of chaetigers 3 and 4 being shorter and stouter than those on chaetigers 2 and 5, and the branchiae of chaetiger 3 having only a basal patch of pinnules instead of having pinnules along ⅔ of the length. Sars (1873) noted regarding the length of the branchiae that “3 die og 2 det Par omtrent ligestore og kun halvt saa lange som første og sidste Par” (the 3rd and 2nd pairs are approximately equal in size, and ½ as long as the first and last pairs). This is also apparent in the provided illustrations (Sars 1873: pl. xvii figs 13–14). Regarding the differences in the distribution of the pinnules on the branchiae of chaetiger 3, it can be considered due to worms studied being of different sizes. Sars (1873) described a specimen that was 30 mm long and 1.5 mm wide, while the only specimen of P. tripinnata was 12 mm long and 0.75 mm wide. Upon examination of the holotype of P. tripinnata, we found it similar to smaller specimens of P. plumosa from Norway and Sweden. Prionospio tripinnata is accordingly considered Fig. 17. Adult and chaetal morphology of Prionospio plumosa M. Sars in G.O. Sars, 1872, neoptype (NHMO C7075). A. Anterior end stained with methylene green, left lateral view. B. Sabre chaetae from neuropodium of chaetiger 30. C. Hooded hooks from neuropodium of chaetiger 30. Abbreviations: see Material and methods. Scale bars: A = 50 μm; B = 10 μm; C = 5 μm. European Journal of Taxonomy 1027: 1–58 (2025) 40 a junior synonym of P. plumosa. The molecular analysis by Hektoen et. al. (2024) also indicated that P. plumosa is present in deep waters in the Eastern Mediterranean. Prionospio plumosa can be distinguished from all other Prionospio by the presence of digitiform pinnules on the branchiae of chaetigers 2, 3 and 5. To our knowledge, it is the only species, together with Prionospio kirrae Wilson, 1990, with pinnules covering the anterior side of the branchiae (the branchiae of chaetiger 5 in P. kirrae) rather than the posterior and/or lateral sides. Dorsal crests in the examined specimens of P. plumosa were present from either chaetiger 6 or 7. The worms sequenced by Hektoen et al. (2024) included specimens with dorsal crests both from chaetiger 6 and 7, indicating that the absence of crest on chaetiger 6 is either intraspecific variation or a preservation artifact. Prionospio plumosa has been noted as rare in taxonomic literature (Sars 1872; Bidenkap 1894; Söderström 1920; Kirkegaard 1996), with sparse records in the 20th century. However, in the last decade, P. plumosa has been frequently reported in ecological surveys near aquaculture sites in Norway. The species was originally described from dead algal fragments (Sars 1873), indicating that the type locality was an area where organic matter accumulated, perhaps mirroring conditions close to modern day finfish farms. Through the examination of unidentified material in various museum collections, additional specimens collected in the 20 th century were discovered, amending the spotty records, including the 1910 neotype (NHMO C7075) and specimens from the Trondheimsfjord (Norway) collected in 1951 (NTNU-VM 25797) and the 1980s (NTNU-VM 25389–25391). Habitats and distribution Prionospio plumosa is common along the Norwegian coast, most often in muddy and silty sediments affected by high organic load at depths of 34–500 m. It has also been recorded from the Mediterranean Sea at depths of 500–1000 m. Prionospio sigvaldadottirae sp. nov. urn:lsid:zoobank.org:act:72F6B797-4133-4B15-937A-C30AF6215151 Figs 18–20; Table 2 Prionospio sp. 7 – Hektoen et al. 2024: figs 1, 4. Diagnosis Prostomium anteriorly truncate, posteriorly extending to end of chaetiger 2 as a narrow caruncle. Four pairs of branchiae on chaetigers 2–5; those on chaetiger 2 long, with lateral pinnules, on chaetiger 5 long or shorter, with lateral pinnules, on chaetigers 3 and 4 shorter, apinnate. Dorsal crests from chaetiger 7 to chaetigers 20–22, highest on chaetiger 7. Neuropodial postchaetal lamellae of chaetiger 2 pointed and elongated ventrally. Sabre chaetiger in neuropodia from chaetiger 10. Hooded hooks in notopodia from chaetigers 43–58, in neuropodia from chaetigers 15–17. Etymology The species is named in honor of Dr Elin Sigvaldadóttir, an Icelandic zoologist who made a great contribution to the study of the Northeastern Atlantic Prionospio. Type material Holotype NORWAY • Norwegian Sea, Vigdis D oil field; 61°21.000′ N 2°4.200′ E; depth 246 m; Aug.–Sep. 2020; STIM AS leg.; stn VTD-10; van Veen grab; NTNU-VM 84143. HEKTOEN M.M. et al., Partial revision of Northern European Prionospio (Annelida: Spionidae) 41 Paratypes NORWAY • 6 specs; Norwegian Sea, Vigdis D oil field; 61°22.009′ N, 2°2.079′ E; depth 246 m; 31 May 2014; STIM AS leg.; stn VTD-R; van Veen grab; NTNU-VM 84145 • 2 specs; Norwegian Sea, Vigdis D oil field; 61°21.000′ N, 2°4.200′ E; depth 246 m; Aug.–Sep. 2020; STIM AS leg.; stn VTD-10; van Veen grab; NTNU-VM 84144 • 6 specs; Norwegian Sea, Vigdis D oil field; 61°20.923′ N, 2°4.176′ E; depth 248 m; Aug.–Sep. 2020; STIM AS leg.; stn VTD-12; van Veen grab; NTNU-VM 84146 • 1 spec.; Vigdis D oil field; 61°20.923′ N, 2°4.176′ E; depth 248 m; Aug.–Sep. 2020; STIM AS leg.; stn VTD-12; van Veen grab; SEM stub; NTNU-VM 85860. Other material examined NORWAY – Norwegian Sea • 1 spec.; Vigdis D oil field; 61°20.923′ N, 2°4.176′ E; depth 250 m; 31 May 2014; STIM AS leg.; stn VTD12_14; van Veen grab; ZMBN 105363 • 1 spec.; Vigdis D oil field; 61°21.000′ N, 2°4.200′ E; depth 246 m; Aug.–Sep. 2020; STIM AS leg.; stn VTD-10; van Veen grab; SEM stub; NTNU-VM 85859.– North Sea • 1 spec.; Oseberg oil field; 60°27′ N, 2°43′ E; depth 104 m; 14 Apr. 1983; stn A10.5; van Veen grab; NTNU-VM 25276 • 1 spec.; Oseberg oil field; 60°27′ N, 2°43′ E; depth 104 m; 5 Jul 1983; stn b7.4; van Veen grab; NTNU-VM 25285 • 1 spec.; Oseberg oil field; 60°27′ N, 2°43′ E; depth 104 m; 5 Jul. 983; stn b5.7; van Veen grab; NTNU-VM 25287 • 1 spec.; Oseberg oil field; 60°27′ N, 2°43′ E; depth 104 m; 5 Jul. 1983; stn b1.gr1; van Veen grab; NTNU-VM 25286 • 1 spec.; Oseberg oil field; 23 Feb. 1984; van Veen grab; NTNU-VM 25275 • 1 spec.; Oseberg oil field; 17 Feb. 1984; van Veen grab; NTNU-VM 25217. Examined material with sequence data NORWAY – Norwegian Sea • 1 spec.; Vigdis D oil field; 61°20.923′ N, 2°4.176′ E; depth 250 m; 31 May 2014; STIM AS leg.; stn VTD12_14; van Veen grab; ZMBN 152646. Fig 18. Prionospio sigvaldadottirae sp. nov., holotype (NTNU-VM 84143), lateral view of anterior end, black spots are sediment rests stuck to the animal. Abbreviations: see Material and methods. Scale bar = 200 μm. European Journal of Taxonomy 1027: 1–58 (2025) 48 either to P. fallax or P. plumosa, while the offshore worms are here referred to P. sigvaldadottirae sp. nov. (see remarks on P. sigvaldadottirae above). No evidence has been found to support the presence of P. steenstrupi in the coastal or shelf waters of mainland Europe, suggesting that the species, if present, is rare in this region. Dagli & Çinar (2009) reported P. steenstrupi from the Eastern Mediterranean, Turkey, with dorsolateral membranous folds as in the Icelandic specimens. However, the Turkish specimens had dorsal crests from chaetiger 7 (rather than from chaetiger 6) and caruncle reaching the end of chaetiger 1 (rather than the end of chaetiger 2) and might represent a yet undescribed species. Species Eye number, shape and size Prostomium shape Caruncle length P. cooki Radashevsky, 2015 two pairs; single spots anteriorly broadly rounded end of chaetiger 4 P. atrovitta Gopal et al., 2020 no eyes narrow, anteriorly rounded end of chaetiger 1 P. cristata Foster, 1971 two pairs; lateral single spot, median comma-shaped anteriorly blunt or rounded end of chaetiger 1 P. depauperata Imajima, 1990 two pairs; lateral single spot, median comma-shaped anteriorly truncate end of chaetiger 2 P. komaeti Hylleberg & Nateewathana, 1991 two pairs; lateral single spot, median larger irregular in shape composed of multiple ocelli anteriorly truncate end of chaetiger 2 P. kulin Wilson, 1990 0-2 pairs; large commashaped anteriorly truncate end of chaetiger 2 P. multicristata Hutchings & Rainer, 1979 two pairs; median commashaped anteriorly broadly rounded end of chaetiger 3 P. oligopinnulata Delgado-Blas, 2015 two pairs; both cup-shaped anteriorly truncate end of chaetiger 1 P. orensanzi Blake, 1983 two pairs; lateral single spot, median larger irregular in shape composed of multiple ocelli anteriorly broadly rounded Middle of chaetiger 2 P. parapari Delgado-Blas, DíazDíaz & Viéitez, 2018 two pairs; lateral pair small, median large crescent anteriorly truncate end of chaetiger 1 P. runei Hylleberg & Nateewathana 1991 one pair, small narrow, anteriorly rounded end of chaetiger 2 P. sigvaldadottirae sp. nov. two pairs; lateral single spot, median weakly crescentic or spots anteriorly truncate end of chaetiger 2 P. steenstrupi sensu Dagli & Çinar, 2009 two pairs of small indistinct subdermal eyes anteriorly truncate end of chaetiger 1 P. variegata Imajima, 1990 two pairs; lateral single spot, median comma-shaped widest anteriorly, rounded end of chaetiger 1 Table 2 (continued on next page). Morphological characteristics of species of the Prionospio steenstrupi Malmgren, 1867 group with dorsal crests on chaetiger 7 and a series of subsequent chaetigers. HEKTOEN M.M. et al., Partial revision of Northern European Prionospio (Annelida: Spionidae) 49 Habitats and distribution Prionospio steenstrupi is only known from Iceland, between 73 and 160 m depth. Prionospio sp. 6 Fig. 22; Table 3 Prionospio sp. 6 – Hektoen et al. 2024: figs 1, 4. Species Sabre chaetae start [chaetiger] Neuropodial hooks start [chaetiger] Lower part of neuropodial lamellae of chaetiger 2 Dorsal crest size Dorsal crest end [chaetiger] Region P. cooki Radashevsky, 2015 10 12–14 ventrally pointed all low 22 Australia P. atrovitta Gopal et al., 2020 15–16 16–18 rounded all low 17 North Indian Ocean P. cristata Foster, 1971 10 11–12 ventrally rounded 7 and 9 high, rest low 12 West Atlantic P. depauperata Imajima, 1990 10 15–16 ventrally pointed 7 high, rest low 13 Japan P. komaeti Hylleberg & Nateewathana, 1991 10 12–18 ventrally pointed 7 high, rest low 11 Thailand P. kulin Wilson, 1990 10 13–21 ventrally pointed 7 high, rest low 17–21 Australia P. multicristata Hutchings & Rainer, 1979 10 14–18 ventrally pointed All low 25–30 Australia P. oligopinnulata Delgado-Blas, 2015 10 12–14 ventrally pointed 7 high, rest low 14 Gulf of Mexico P. orensanzi Blake, 1983 10 20 rounded ? 19 Argentina P. parapari Delgado-Blas, Díaz-Díaz & Viéitez, 2018 10–13 11–15 ventrally pointed 7 high, rest low 9 Spain P. runei Hylleberg & Nateewathana, 1991 10 8–12 rounded all low 9 Thailand P. sigvaldadottirae sp. nov.10 16–18 ventrally pointed 7 high, rest low 20–22 East Atlantic P. steenstrupi sensu Dagli & Çinar, 2009 10 14–16 ventrally pointed 7 high, rest low 18 Eastern Mediterranean P. variegata Imajima, 1990 10 11 rounded all low 14 Japan Table 2 (continued). European Journal of Taxonomy 1027: 1–58 (2025) 50 Diagnosis Prostomium narrow, anteriorly rounded, posteriorly extending to middle of chaetiger 1 as a short caruncle. Eyes absent. One pair of apinnate branchiae on chaetiger 3. Notopodial postchaetal lamellae of chaetiger 3 largest, rounded, of chaetigers 2 and 4 triangular. Dorsal crests absent. Neuropodial postchaetal lamellae oblong. Sabre chaetae in neuropodia from chaetiger 10. Hooded hooks in neuropodia from chaetigers 10–11. Material examined NORWAY – Vestland • 1 spec.; Høyanger, Torvund; 61.13583° N, 5.75473° E; depth 1255 m; 3 May 2017; Bergen University Museum leg.; stn KB2017-05-05GR; van Veen grab; SEM stub; ZMBN 152561 • 1 spec.; Bømlo, Sveio; 59.56729° N, 5.21568° E; depth 328 m; 28 Apr. 2017; Bergen University Museum leg.; stn KB-20; van Veen grab; ZMBN 152636. Examined material with sequence data NORWAY – Vestland • 1 spec; Sognefjorden; 61.05012° N, 5.40056° E; depth 1236 m; 3 May 2017; Bergen University Museum leg.; stn kb2017-05-02; van Veen grab; ZMBN 152637. Description Three specimens examined, all 0.1 mm wide or smaller. One specimen likely complete, but damaged posteriorly, in three fragments totaling 40 chaetigers. Color in alcohol pale white. Prostomium narrow, anteriorly rounded (Fig. 22A–B), extending to middle of chaetiger 1 as a short caruncle. Eyes absent. Posterior dorsolateral parts of peristomium fused with notopodial postchaetal lamellae of chaetiger 1 forming ear-shaped structures lateral to prostomium. Palps in one specimen, broken, as long as four chaetigers (Fig. 22A). One pair of branchiae on chaetiger 3 in all three specimens, with no scars visible on other chaetigers. Branchiae apinnate, with lateral ciliation, triangular, shorter than notopodial postchaetal lamellae on the same chaetiger (Fig. 22A). Nototrochs transverse ciliary bands between branchial bases. Dorsolateral longitudinal ciliation absent. Fig. 22. Morphology of Prionospio sp. 6 (ZMBN 152561), SEM micrographs. A. Anterior end, left dorsolateral view. B. Closeup of same specimen. Abbreviations: see Material and methods. Scale bars: A = 200 μm; B = 50 μm. HEKTOEN M.M. et al., Partial revision of Northern European Prionospio (Annelida: Spionidae) 51 Notopodial prechaetal lamellae inconspicuous. Notopodial postchaetal lamellae of chaetiger 1 rounded, fused with peristomium. Lamellae of chaetiger 2 triangular; lamellae of chaetiger 3 greatly enlarged, rounded, with a small, elongated tip; lamellae triangular on chaetiger 4, rounded on chaetiger 5, lower and oval-shaped on succeeding chaetigers. Dorsal crests absent. Neuropodial prechaetal lamellae inconspicuous. Neuropodial postchaetal lamellae of chaetiger 1 small and oblong; lamellae of chaetigers 2–7 rectangular, broader than high; lamellae lower and rounded on succeeding chaetigers (Fig. 22A–B). Interneuropodial pouches absent. Capillary chaetae in single rows in all chaetigers, alimbate and smooth. Sabre chaetae in neuropodia from chaetiger 10. Hooded hooks in notopodia not observed. Hooded hooks in neuropodia from chaetigers 10–11. Pygidium missing in all specimens. Species No. of chaetigers with branchiae Branchae from [chaetiger] Dorsal crests Sabre chaetae start [chaetiger] Neuropodial hooded hooks start [chaetiger] Distribution Width (mm) A. abranchiata Neal, Paterson & Soto, 2016 0 – present 10 11–12 Porcupine abyssal plain 0.2 A. dibranchiata Maciolek, 1981 2 3 present or absent 9–11 10 Atlantic Ocean 0.2 A. foodbancsia Mincks, Dyal, Paterson, Smith & Glover, 2009 1 3 present 10 11 Antarctica 0.2 P. alexandrae Peixoto & Paiva, 2020 2 2 absent absent 10–20 Brazil 0.25 P. branchilucida Altamira, Glover & Paterson, 2016 2 2 present absent 11 Brazil 0.08 P. hermesia Neal & Paterson, 2016 2 2 present absent 13–14 Portugal, deep sea 0.08 P. kaplani Altamira, Glover & Paterson, 2016 2 2 present absent 11 Atlantic and Pacific deep sea 0.08 P. nonatoi Peixoto & Paiva, 2019 0 – present 10 11–12 Brazil 0.18 P. solisi Peixoto & Paiva, 2019 2 3 absent 9–11 9–14 Brazil 0.25 P. sp. 6 1 3 absent 10 10–11 Norwegian coast 0.1 Table 3. Morphological characters of species of Prionospio Malmgren, 1867 and Aurospio Maciolek 1981 with less than three pairs of branchiae. European Journal of Taxonomy 1027: 1–58 (2025) 52 Remarks Prionospio sp. 6 is represented only by three small incomplete specimens which could be juveniles with not yet fully developed features. Although molecular data of one of these specimens distinguished it from other Prionospio (Hektoen et al. 2024: figs 1, 4), we do not formally name it pending examination of additional specimens. The species does bear resemblance to other small-sized species of Prionospio and Aurospio but can be distinguished morphologically from all such species (Table 3). Habitats and distribution Prionospio sp. 6 was collected from Norwegian fjords in the northern part of the North Sea and southern part of the Norwegian Sea. Worms were found in silty and muddy sediments at depths of 328–1255 m. Identification key to the species of adult Prionospio Malmgren, 1867 in Northern Europe 1. At least some branchiae with pinnules ............................................................................................. 2 – All branchiae apinnate ...................................................................................................................... 6 2. Pinnate branchiae on chaetigers 2, 3 and 5, pinnules on branchiae of chaetiger 3 may only be present basally .................................................................... Prionospio plumosa M. Sars in G.O. Sars, 1872 – Pinnate branchiae otherwise ............................................................................................................. 3 3. Dorsal crests absent ......................................Prionospio multisetosa Delgado-Blas & Peraza, 2024 – Dorsal crests present ......................................................................................................................... 4 4. High dorsal crest present on chaetiger 7 only ........................... Prionospio fallax Söderström, 1920 – Dorsal crests present on more than one chaetiger ............................................................................ 5 5. Dorsal crests from chaetiger 6, membranous folds between successive notopodia on some chaetigers between chaetigers 4 and 17 ...............................................Prionospio steenstrupi Malmgren, 1867 – Dorsal crests from chaetiger 7, membranous folds between successive notopodia absent ................. ...................................................................................................Prionospio sigvaldadottirae sp. nov. 6. One pair of branchiae on chaetiger 3 ........................................................................ Prionospio sp. 6 – More than one pair of branchiae ....................................................................................................... 7 7. 2–5 pairs of branchiae from chaetiger 2 or 3 (usually three pairs of branchiae from chaetiger 3). Low dorsal crests from chaetiger 6–9 ............................................Prionospio banyulensis Laubier, 1966 – At least five pairs of branchiae from chaetiger 2. Dorsal crests from chaetiger 10 or later ............. 8 8. Up to six pairs of branchiae. Prostomium extending to end of chaetiger 2. Lower part of neuropodial postchaetal lamellae of chaetiger 2 elongated and pointed downwards ............................................. ................................................................................................Prionospio cirrifera Wirén, 1883 agg. – Up to 13 pairs of branchiae. Prostomium extending at the most to the middle of chaetiger 2. Lower part of neuropodial postchaetal lamellae of chaetiger 2 rounded ..................................................... 9 9. Prostomium anteriorly rounded, narrow caruncle extending to middle of chaetiger 2. Median eyes small or large ..............................Prionospio sanmartini Delgado-Blas, Díaz-Díaz & Viéitez, 2019 – Prostomium triangular, anteriorly truncate, thick caruncle extending to end of chaetiger 1. Eyes indistinct in all individuals ..................................................................... Prionospio fiordica sp. nov. HEKTOEN M.M. et al., Partial revision of Northern European Prionospio (Annelida: Spionidae) 53 Discussion A commonality between many contemporary studies on polychaete diversity is that species have less intraspecific morphological variation and more limited geographical distribution than previously estimated (e.g., Hutchings & Kupriyanova 2018; Nygren et al. 2018; Grosse et al. 2020). Species of Prionospio seem to be at least partly an exception to this. Molecular studies have shown that species of Prionospio can be widely distributed in both the deep sea (Guggolz et al. 2020; Neal et al. 2022) and coastal waters (Hektoen et al. 2024). In addition to what was already found by Hektoen et al. (2024) we here found no morphological distinctions between East and West Atlantic specimens of P. steenstrupi, or Norwegian and West African specimens of P. multisetosa and P. sigvaldadottirae sp. nov. In addition to their broad geographic ranges, several species of Prionospio in our study also displayed substantial bathymetric distributions. The most notable examples include P.fiordica, recorded from depths between 328 and 1236 meters, and P. multisetosa, found between 47 and 665 meters. These depth ranges were largely confirmed by molecular species delimitation (Hektoen et al. 2024). However, it is important to note that many of the deeper records originate from Norwegian fjords. These fjord systems, while deep, are enclosed and exhibit oceanographic conditions that differ markedly from those of the open deep sea (Oug et al. 2010). As such, the ecological barriers associated with depth in these environments may not be as pronounced as in non-coastal ecosystems. With this review, we have identified ten species of Prionospio in samples from northern European waters, up from seven reported previously. The diversity of Prionospio is much better understood than in previous centuries; however, there is still much to be studied and understood. For example, Prionospio sp. 6 was left unresolved here. More specimens are needed to describe and name this species. The small size of available specimens and their morphology could indicate that we dealt with juveniles. These specimens are morphologically similar to species of Prionospio and Aurospio described from the deep sea (Paterson et al. 2016; João et al. 2019; Peixoto & Paiva 2019) or the Antarctic shelf (Mincks et al. 2009), such as very small size, greatly enlarged notopodial postchaetal lamellae and reduced number of branchiae. Prionospio sanmartini also require further revision. Additional specimens of P. sanmartini of different sizes are needed to better understand the morphological variability of this species and taxonomic relationships between the Spanish and Nordic populations. The molecular study of Hektoen et al. (2024) also indicated that P. cirrifera likely comprises two or three species in Northeast Atlantic and Arctic waters. This species complex will be treated separately in an upcoming study. We decided not to designate a neotype and redescribe P. dubia based on the 13 available specimens from South Africa. Since these specimens were a mix from nine different stations, it was impossible to know the sampling locality of a potential neotype. The type of P. dubia may also still exist under a different name, as it was first described as a variety of P. malmgreni and later referred to P. steenstrupi. It is even unclear whether the 13 studied specimens are conspecific or comprise more than one species as some of them have eyes while others lack. It becomes clear that more specimens from South Africa should be collected and studied to elucidate the specific morphological and molecular characteristics of P. dubia. Acknowledgments This work is a part of the project “Monitoring of marine ecosystems: Challenges in cryptic speciation and eDNA metabarcoding” supported by the Research Council of Norway project no. 298961. This project would not have been possible without access to material deposited in different institutions. In this regard we would like to thank Jon A. Kongsrud and Tom Alvestad (ZMBN), Lena Gustavsson (SMNH), Karen Osborn and Karen Reed (USNM), Javier Ignacio Sánchez Almazán (MNCN), Hans Mejlon (UPSZTY), and Ann-Helén Rønning (NHMO). We would also like to thank Martin Skarsvåg (STIM AS) and Gunhild Borgersen (NIVA) for providing specimens for the study. We wish to thank Thi My Linh Hoang (Cellular & Molecular Imaging Core Facility, NTNU) for assistance in the scanning European Journal of Taxonomy 1027: 1–58 (2025) 54 electron microscopy lab. We thank two reviewers for constructive comments that helped to improve the manuscript. 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