New species of Anguillosyllis Day, 1963 (Annelida, Syllidae) from polymetallic nodule exploration areas, eastern Clarion-Clipperton Zone, central Pacific Ocean

30 European Journal of Taxonomy 1026: 30–64 https://doi.org/10.5852/ejt.2025.1026.3105 europeanjournaloftaxonomy.eu ISSN 2118-9773 2025 · Neal L. et al. This work is licensed under a Creative Commons Attribution License (CC BY 4.0) Received: 8 August 2024 • Accepted: 12 August 2025 • Published: 11 November 2025 Topic editor: Magalie Castelin • Section editor: Nataliya Budaeva • Desk editor: Pepe Fernández Research article urn:lsid:zoobank.org:pub:A9D6F837-22FC-4371-98CC-E1E6D6812BA8 New species of Anguillosyllis Day, 1963 (Annelida, Syllidae) from polymetallic nodule exploration areas, eastern Clarion-Clipperton Zone, central Pacific Ocean Lenka NEAL1,* , Regan DRENNAN 2 , Helena WIKLUND3 , Eva C.D. STEWART 4 , Muriel RABONE 5 , Thomas G. DAHLGREN 6 & Adrian G. GLOVER 7 1,2,3,4,5,7 Life Sciences Department, Natural History Museum, London, SW7 5BD, UK. 3,6 Department of Marine Sciences, University of Gothenburg, Box 463, 40530 Gothenburg, Sweden. 3,6 Gothenburg Global Biodiversity Centre, Box 463, 40530 Gothenburg, Sweden. 4 School of Ocean and Earth Sciences, University of Southampton, Southampton, SO14 3ZH, UK. 6 NORCE Norwegian Research Centre, P.O.B. 22 Nygårdsgaten, NO-5838 Bergen, Norway. *Corresponding author: [email protected] 2 Email: r[email protected] 3 Email: [email protected] 4 Email: [email protected] 5 Email: [email protected] 6 Email: [email protected] 7 Email: [email protected] Abstract. The benthic annelid fauna of polymetallic nodule fields in the eastern Clarion-Clipperton Zone (CCZ), abyssal Central Pacific has recently been the subject of taxonomic investigations aiming to document the biodiversity of this region. While annelids are abundant and diverse within the CCZ, particularly high diversity was discovered within the syllid genus Anguillosyllis Day, 1963 from material collected during environmental surveys targeting exploration contract areas ‘UK-1’, ‘OMS’ and ‘NORI-D’, as well as Area of Particular Environmental Interest, ‘APEI-6’. From the total Anguillosyllis material examined (134 specimens), 37 specimens were amenable to the formalization of three new species: Anguillosyllis dalgleishae sp. nov., A. finnelli sp. nov., and A. villarae sp. nov. Prior to this study, 20 species of Anguillosyllis were known worldwide and only two species were known from the CCZ – A. truebloodi Maciolek, 2020 and A. hessleri Maciolek, 2020. Keywords. CCZ, deep-sea mining, taxonomic novelty, species distribution, molecular phylogeny, 18S, 16S, COI. Neal L., Drennan R., Wiklund H., Stewart E.C.D., Rabone M., Dahlgren T.G. & Glover A.G. 2025. New species of Anguillosyllis Day, 1963 (Annelida, Syllidae) from polymetallic nodule exploration areas, eastern ClarionClipperton Zone, central Pacific Ocean. European Journal of Taxonomy 1026: 30–64. https://doi.org/10.5852/ejt.2025.1026.3105 NEAL L. et al., New species of Anguillosyllis (Syllidae, Annelida) from the CCZ 31 Introduction The Clarion-Clipperton Zone (CCZ) polymetallic nodule area in the central abyssal Pacific Ocean has been explored in recent decades for its deep-sea mineral resources and their potential for commercial mining (e.g., Gollner et al. 2017; Glover et al. 2018; Jones et al. 2021; Smith et al. 2021). The exploration licenses are issued to Sponsoring States by the International Seabed Authority (ISA), which stipulates the need for environmental impact assessments and the establishment of preservation areas (Lodge et al. 2014; Jones et al. 2021; Washburn et al. 2021). Here, we concentrate on such studies within areas of the eastern CCZ prospected by 1) the UK Seabed Resources Ltd (UKSRL) exploration contract area ‘UK-1’, 2) the Ocean Mineral Singapore exploration contract area ‘OMS’, 3) Area of Particular Environmental Interest, ‘APEI-6’ and 4) Nauru Ocean Resources Inc (NORI) (a subsidiary of The Metals Company), which holds exploration rights to four areas (A, B, C and D) and is authorised to carry out its mineral exploration activities in the area of the Republic of Nauru. Knowledge of the biodiversity and distribution of benthic taxa found within areas of potential mining operations is paramount to informed environmental impact assessments and conservation efforts (e.g., Smith et al. 2011, 2021; Jones et al. 2021; Rabone et al. 2023a, 2023b). Both biodiversity and species ranges remain poorly understood mainly due to under-sampling and the lack of comparable datasets produced by different research groups and contractors. The latter factor is compounded by the lack of formal taxonomic descriptions of the fauna, given that most represent species new to science. Sediment infauna, while comparatively better studied and to a higher resolution than other faunal categories such as nodule fauna or megafauna (Rabone et al. 2023a), cannot be captured by video or camera surveys limiting the size of the datasets. In general, annelid worms dominate the abyssal sediment macrofauna, constituting 50–75% of macrofaunal abundance and species richness, and are therefore considered a key component of benthic biodiversity (e.g., Glover et al. 2002; Smith et al. 2008; Stewart et al. 2023). Annelids also exhibit a broad range of feeding types and life-history strategies and are frequently used to evaluate anthropogenic disturbance in shallow-water habitats (Dean 2008). Thus, evaluation of the diversity and species ranges of annelid worms is critical to predicting and managing the impacts of nodule mining in the CCZ. Our main objective has been to provide taxonomic and genetic data on macrofaunal annelids collected from the targeted areas within the CCZ. These data build on previous taxonomic works on annelid worms from the target areas (Wiklund et al. 2019, 2023; Drennan et al. 2021; Neal et al. 2022a, 2022b, 2023), as well as the wider CCZ area (e.g., Janssen et al. 2015; Bonifácio & Menot 2018; Blake 2019; Bonifácio et al. 2020, 2024; Maciolek 2020). Currently, 52 new annelid species have been formally described from the CCZ (Rabone et al. 2023b, 2024), with a focus on Spioniformia (Paterson et al. 2016; Guggolz et al. 2020; Neal et al. 2022a), Polynoidae Kinberg, 1856 (Bonifácio & Menot 2018), Cirratulidae Ryckholt, 1851 (Blake 2019), Opheliidae Malmgren, 1867, Scalibregmatidae Malmgren, 1867 and Travisiidae Hartmann-Schröder, 1971 (Wiklund et al. 2019), Nereididae Blainville, 1818 (Drennan et al. 2021), Amphinomida Lamarck, 1818 (Neal et al. 2022b) and Syllidae Grube, 1850 (Nilsson et al. 2024), including Anguillosyllis Day, 1963 (Maciolek 2020). While targeting the annelid family Syllidae Grube, 1850, it has been noted that the majority of specimens found in the CCZ samples belong to the genus Anguillosyllis. Anguillosyllis is a rather enigmatic taxon within Syllidae, although its placement within this family based on morphology alone is ambiguous as it displays intermediate morphological characters between traditional Syllidae subfamilies (Aguado & San Martín 2008). The absence of pharyngeal armature has been observed in Anoplosyllinae Aguado & San Martín, 2009, while the smooth and long dorsal cirri are known in Eusyllinae Malaquin, 1893 and one pair of peristomial cirri, and ovate to papilliform antennae in Exogoninae Langerhans, 1879 (a subfamily in which Anguillosyllis was originally placed, based on A. capensis Day, 1963 having fused palps). Phylogenetic analyses, that incorporated both molecular and morphological data, recovered this genus as a basal sister taxon to all Syllidae (Aguado et al. 2012). European Journal of Taxonomy 1026: 30–64 (2025) 32 The genus was established for a single species, Anguillosyllis capensis, found in 183 m water depth off South Africa (Day 1963). The distinct appearance of this species due to characters such as short body and greatly elongated palps has made this species ‘easy to recognize’ and as a result it has been reported across a wide geographic and bathymetric range (Böggemann & Purschke 2005; Böggemann 2009). A further two species were assigned to Anguillosyllis by revisional work of Aguado & San Martín (2008). They examined specimens of Braniella pupa Hartman, 1965 from bathyal NW and SW Atlantic and B. palpata Hartman, 1967 from the Southern Ocean and noting the similarities between the two genera, declared Braniella Hartman, 1965 to be a junior synonym of Anguillosyllis. More recently, Barroso et al. (2017) described a new species, A. lanai, from 1035–2997 m on the continental slope off southeastern Brazil. Several undescribed species have also been reported in deep waters worldwide (e.g., Aguado et al. 2012; Langeneck et al. 2018; Neal et al. 2020; Gunton et al. 2021), suggesting that this enigmatic taxon may in fact be more common than previously thought. An important contribution to the taxonomy of this genus was recently made by Maciolek (2020). Using collections from several deep-sea studies worldwide and examining ca 1400 specimens, Maciolek (2020) recognized and newly described 16 species, bringing the total number of species in the genus to 20. Her work provided further observations of morphological characters considered of taxonomic importance by previous workers (e.g., Aguado & San Martín 2008; Barroso et al. 2017) such as number of chaetigers in adults, degree of fusion of the palps, degree of development of parapodial lobes, structure and number of internal and external glands, number of chaetae in anterior chaetigers, shape and size of proventricle, annulation of the dorsum, and presence of four anal cirri. Among the newly described species by Maciolek (2020), two were reported from the CCZ – Anguillosyllis truebloodi Maciolek, 2020 and A. hessleri Maciolek, 2020. However, up to four genetic lineages were recently found in specimens morphologically identified as A. hessleri (Drennan et al. 2025). Ongoing work suggests a much greater diversity of Anguillosyllis existing within the CCZ, with ~ 30 putative species recognized using a combination of morphological and/or molecular approaches (Neal pers. obs.). The majority of remaining putative species will be covered in a separate data publication (sensu Wiklund et al. 2023), as specimen damage and small numbers of individuals prevents full formal description of so many of these species. Here, we concentrate on the material amenable to taxonomic formalization, describing three new species: Anguillosyllis dalgleishae sp. nov., A. finnelli sp. nov., and A. villarae sp. nov., and providing a discussion of notable taxonomic characters in the genus. Material and methods Fieldwork The first UKSR ABYSSLINE cruise (AB01) took place in October 2013 onboard the RV Melville and targeted the UK-1 exploration contract area (Fig. 1). The second cruise (AB02) took place in FebruaryMarch 2015 onboard the RV Thomas G. Thompson and sampled a wider area (Fig. 1), including: UK-1 (depth ~ 4200 m) and OMS (depth ~ 4200 m) exploration contract areas, and APEI-6 (depth ~ 4050 m). The Resource Cruise 01 (RC01) took place aboard the MV Pacific Constructor between February and March 2020 and targeted exploration contract areas UK-1 and OMS (Fig. 1). Nauru Ocean Resources Inc. (NORI) Campaign 05a took place October to November 2020 and campaign 05d from April to June 2021, both onboard the Maersk Launcher, to the NORI-D exploration area (depth ~ 4300 m) (Fig. 1). Nauru Ocean Resources Inc. (NORI) Campaigns 07a and 07b took place onboard the Ocean Infinity vessel Island Pride in August 2022 and between November and December 2022, respectively (Fig. 1). The SMARTEX (Seabed Mining And Resilience To EXperimental impact) cruise JC241 took place between February and March 2023 onboard the RRS James Cook and sampled the Ocean Minerals Company (OMCO) 1979 mining collector test area (depth ~ 4700 m) (Fig. 1). NEAL L. et al., New species of Anguillosyllis (Syllidae, Annelida) from the CCZ 33 Fig. 1. Sampling sites showing occurrence of Anguillosyllis spp. A. Map of the nodule exploration contract areas, reserved areas, and Areas of Particular Environmental Interest (APEI) in the ClarionClipperton Zone (CCZ), central Pacific Ocean, showing the areas considered in this study (in colour), insert shows the position of CCZ to the continent. B. Nauru Ocean Resources Inc. license area D (NORI-D). C. Ocean Minerals Company (OMCO) 1979 mining collector test area. D. Ocean Minerals Singapore license area. E. UK seabed resources UK-1 license area. European Journal of Taxonomy 1026: 30–64 (2025) 34 For a comprehensive description of the methodological pipeline see Glover et al. (2016). Briefly, specimens were collected using box corers or a Brenke Epibenthic Sledge, with sediment sieved on 300 µm mesh size on board the vessels. Geographic data from sampling activities were recorded on a central GIS database (Fig. 1). Live-sorting of specimen samples was carried out onboard the vessels in a ‘cold-chain’ pipeline, with material maintained in chilled (2–4°C), filtered seawater. Specimens were assigned preliminarily identifications and imaged live using stereo microscopes with attached digital cameras (Glover et al. 2016). Specimens were then stored in individual microtube vials filled with aqueous solution of 80% non-denatured ethanol labelled appropriately and entered into a database. Samples were kept chilled throughout their transportation to the Natural History Museum, London, UK. Morphological laboratory work In the laboratory, preserved specimens were re-examined using stereo and compound microscopes with key morphological features photographed with digital camera. ‘Shirlastain A’ (SDL Atlas Textile Testing Solutions) was used during the morphological examination on some specimens, to ease observation of certain characters. Methyl Green stain was used to observe staining of internal glands. Scanning electron microscopy (SEM) using a SEM FEI Quanta 650 FEG was conducted on selected specimens (n = 3), following graded ethanol dehydration, critical point drying, and gold coating. Figures were assembled using Adobe Photoshop CS6 software. Molecular laboratory work Extraction of DNA was done with DNeasy Blood and Tissue Kit (Qiagen) using a Hamilton Microlab STAR Robotic Workstation, or with QuickExtract TM DNA extraction solution (Lucigen), following manufacturer guidelines, and adapted for a digestion time of 45 minutes. One nuclear gene (18S) and two mitochondrial genes (COI, 16S) were targeted for sequencing. Approximately 1800 bp of 18S were amplified using the primers 18SA 5′-AYCTGGTTGATCCTGCCAGT-3′ (Medlin et al. 1988) and 18SB 5′-ACCTTGTTACGACTTTTACTTCCTC-3′ (Nygren & Sundberg 2003). Around 450 bp of 16S were amplified with the primers ann16Sf 5′-GCGGTATCCTGACCGTRCWAAGGTA-3′ (Sjölin et al. 2005) and 16SbrH 5′-CCGGTCTGAACTCAGATCACGT-3′ (Palumbi 1996), and around 650 bp of COI (cytochrome c oxidase subunit 1) were amplified using LCO1490 5′-GGTCAACAAATCATAAAGATATTGG-3′ (Folmer et al. 1994) and COI-E 5′-TATACTTCTGGGTGTCCGAAGAATCA-3′ (Bely & Wray 2004) or polyLCO 5′-GAYTATWTTCAACAAATCATAAAGATATTGG-3′ and polyHCO 5′-TAMACTTCWGGGTGACCAAARAATCA-3′ (Carr et al. 2011). The PCR mix for each reaction contained 10.5 µl of Red Taq DNA Polymerase 1.1X MasterMix (VWR), 0.5 µl of each primer (10 µm), and 1 µl of DNA template. PCR amplification profiles for each marker were as follows: 18S – initial denaturation of 5 mins at 95°C followed by 30 cycles of 30 s at 95°C, 1 min at 59°C, 2 min at 72°C, with a final extension of 2 min at 72°C; 16S – initial denaturation of 5 mins at 94°C followed by 35 cycles of 30s at 94°C, 30s at 57°C, 1 min at 68°C, with a final extension of 7 min at 68°C; COI – initial denaturation of 5 mins at 95°C followed by 35 cycles of 30 s at 95°C, 30 s at 49°C, 1 min at 74°C, with a final extension of 10 min at 74°C. PCR products were purified using a Millipore Multiscreen 96-well PCR Purification System, and sequencing was performed on an ABI 3730XL DNA Analyser (Applied Biosystems) at The Natural History Museum Sequencing Facility, using the same primers as in the PCR reactions plus two internal primers for 18S, 620F 5′-TAAAGYTGYTGCAGTTAAA-3′ (Nygren & Sundberg 2003) and 1324R 5′-CGGCCATGCACCACC-3′ (Cohen et al.1998). Overlapping sequence fragments were merged into consensus sequences using Geneious (Kearse et al. 2012) and aligned using MAFFT (Katoh 2002) for 18S and 16S, and MUSCLE (Edgar 2004) for COI, both programs used as plugins in Geneious, with default settings. COI alignments were translated into amino acids in order to check for stop codons and avoid the inclusion of pseudogenes. Sequences were compared against all COI, 16S, and 18S sequence data available on the public database GenBank (NCBI), using the blastn algorithm (Johnson et al. 2008) via the Geneious plugin with default settings. NEAL L. et al., New species of Anguillosyllis (Syllidae, Annelida) from the CCZ 35 Alignments were also created using all available CCZ Anguillosyllis sequences and all Anguillosyllis sequences available on GenBank. Distances within and between putative species of Anguillosyllis were calculated from these alignments using the p-distance and Kimura’s two parameter (K2P) (Kimura 1980) models with default settings in MEGA ver. 11 (Tamura et al. 2021). A combined Bayesian phylogenetic analysis of all three genes was conducted with MrBayes ver. 3.2.6 (Ronquist et al. 2012). This dataset included representatives of the three Anguillosyllis sp. nov. presented in this study, with representatives of the Anguillosyllis cf. hessleri complex (Drennan et al. 2025), and additional Anguillosyllis sequences and representative syllid outgroups from GenBank (Supp. file 1: Table S1). The most suitable substitution model for each gene was chosen using Modeltest-NG (Darriba et al. 2020) and the Bayesian information criterion (BIC) and adapted for MrBayes. The most suitable model for each gene position was GTR+I+G. Analyses were run for 10 million generations under default settings, with 2.5 million discarded as burnin. The IQ-TREE online web server tool (W-IQ-TREE, Trifinopoulos et al. 2016) was used to perform maximum likelihood (ML) phylogenetic analyses for the combined gene dataset and for separate 16S and COI alignments including all sequenced individuals of the three species of Anguillosyllis presented in this study. The best fitting models for these analyses were assessed and assigned automatically using the W-IQ-TREE ModelFinder function (Kalyaanamoorthy et al. 2017) using the Bayesian information criterion. Substitution models were as follows: combined 18S: TNe+G4, 16S: GTR+F+I+G4, COI: K3Pu+F+I+G4; separate 16S: GTR+F+I+G4; separate COI: TIM+F+I+G4. All ML analyses were conducted with 1000 bootstrap pseudoreplicates using the ultrafast bootstrap approximation algorithm (Minh et al. 2013; Hoang et al. 2018). All trees were visualized using FigTree ver. 1.4.4 (Rambaut 2018) and edited using Adobe Illustrator. Nomenclatural assignments Continuing the tradition of the NHM deep-sea research group, formalized species were named in honour of the scientists, technicians, and crew of the vessels used to collect them, with the names being randomly selected from a list of all on board. Type material, DNA specimen vouchers and DNA extractions are deposited at the Natural History Museum (NHM), London. A full list of all taxa including Natural History Museum Accession Numbers (NHMUK), NHM Molecular Collection Facility (NHM-MCF), and NCBI GenBank accession numbers is provided in Table 1. Data handling The field and laboratory work led to a series of databases and sample sets that were integrated into a ‘data-management pipeline’. This included the transfer and management of data and samples between a central collections database, a molecular collections database and external repositories (GenBank, WoRMS, OBIS, GBIF, GGBN, ZooBank) through Darwin Core archives. This provides a robust data framework to support DNA taxonomy, in which openly available data and voucher material are key to quality data standards. A further elaboration of the data pipeline is published in Glover et al. (2016). List of acronyms ABYSSLINE = ABYSSal baseLINE ANEA = Annelida APEI = Area of Particular Environmental Interest CCZ = Clarion-Clipperton Zone ISA = International Seabed Authority NHM = Natural History Museum London NORI = Nauru Ocean Resources Inc. OMCO = Ocean Minerals Company OMS = Ocean Mineral Singapore European Journal of Taxonomy 1026: 30–64 (2025) 36 TMC = The Metals Company UKSRL = UK Seabed Resources Ltd. RC01 = Resource cruise SMARTEX = Seabed Mining And Resilience To EXperimental Impact Results Phylum Annelida Lamarck, 1802 Class Polychaeta Grube, 1850 Order Phyllodocida Dales, 1962 Family Syllidae Grube, 1850 Genus Anguillosyllis Day, 1963 Type species Anguillosyllis capensis Day, 1963. Diagnosis (amended from Maciolek 2020) Body very small, adults with limited and fixed number of chaetigers (8–11). Palps elongated, free to the base or fused partly to completely. Prostomium with three antennae, without eyes. Peristomium with one pair of tentacular cirri similar to or smaller than prostomial antennae. Parapodia uniramous, with anterior and posterior lobes developed to varying degrees; with superior (dorsal) lobe that may be contractile. Dorsal cirri may be absent on a variable number of chaetigers, with true absence on chaetiger 2 or on all chaetigers except chaetiger 1. Compound chaetae heterogomph, with falcigers and spiniger-like blades. Falcigers unior bidentate. Pharynx straight, eversible, with two (or three) crowns or sections, external one formed by pharyngeal sheath, distal one surrounded by several (10–12) soft papillae, tooth absent. Proventricle cylindrical, usually tapered posteriorly, muscle rows obscure; with associated glandular structure wrapped around post-ventricle. Pygidium with four cirri, two lateral, two ventromedial. Remarks While the distinct look of Anguillosyllis (elongated palps, low number of chaetigers) might have contributed to the lumping of similar species in the past, the use of molecular techniques has revealed a far greater diversity within this genus than previously thought (Drennan et al. 2025). Recent taxonomic work reported on characters that could help differentiate between different species (Aguado & San Martín 2008; Barroso et al. 2017; Maciolek 2020). Most recently, Drennan et al. (2025) revealed novel and previously overlooked characters, best observed with the use of SEM, such as a complex form of prostomium, and absence of dorsal cirri on all but chaetiger 1. Here we rely predominantly on the characters used by Maciolek (2020), supplemented with SEM observations where possible. We caution against reliance on the characters such as size and shape of antennae or dorsal cirri, as these can differ even within a single specimen (Neal pers. obs.), likely due to preservation. Update on previously reported characters Palpal length can range from short (defined as similar in length to prostomium), to elongate (equaling multiple lengths of prostomium, usually no more than twice the length of prostomium), while the shape of palps can be pointed, conical or finger-like. Prostomial antennae can vary in size (relative to prostomium and lateral antennae relative to median antenna) and in shape being papilliform, digitiform, club-shaped, cirriform or ovate, although caution is needed as stated above. NEAL L. et al., New species of Anguillosyllis (Syllidae, Annelida) from the CCZ 37 Table 1 (continued on next page). List of taxa presented in this paper with cruise record number, GUID (Global Unique Identifier link to data record at http://data.nhm.ac.uk), NHMUK accession number, NHMUK Molecular Collection Facility (MCf) sample ID number (NHMUK_MCF#) and NCBI GenBank accession number (Genbank#) for successfully sequenced genetic markers. GenBank numbers for phylogenetic analysis downloaded from GenBank are presented in Supp. file 2: Table S2. SpeciesSpecimen record no. GUID MCf no. NHMUK reg. # GenBank Acc. # COI/16S/18S Anguillosyllis dalgleishae sp. nov. NHM_837 42eab9a3-1d5c-43ec-86e2-4f5aa47bd5f1 0174126329 ANEA 2024.2686 (paratype) …./PV579009/… Anguillosyllis dalgleishae sp. nov. NHM_1021 d5d9b8f4-8717-43e7-9e6f-422ce4acfdb6 0174126318 ANEA 2024.2687 …/PV579010/… Anguillosyllis dalgleishae sp. nov. NHM_1201 889e12a1-6e88-4987-9e8a-1d758fd43ea3 0174126305 ANEA 2024.2688 …/PV579011/… Anguillosyllis dalgleishae sp. nov. NHM_1347A 4be32c49-79e4-4cb1-a7b2-12b6265ff348 0174126294 ANEA 2024.2689 (paratype) PV577541/PV579012/… Anguillosyllis dalgleishae sp. nov. NHM_1508C 502bcd95-9ec8-4ed2-acea-e630ede84474 0174126281 ANEA 2024.2690 PV577525/PV579013/… Anguillosyllis dalgleishae sp. nov. NHM_1597 f4490e8c-6091-4f27-85df-982e78912412 0174126245 ANEA 2024.2691 …/PV579014/… Anguillosyllis dalgleishae sp. nov. NHM_1657 e40b2e1f-f476-4085-9993-6dcf1221d8ad 0174126270 ANEA 2024.2692 …/PV579015/… Anguillosyllis dalgleishae sp. nov. NHM_1773 589cb9f8-292c-4668-940d-b2891384e4c0 0174126328 ANEA 2024.2693 …/PV579016/… Anguillosyllis dalgleishae sp. nov. NHM_1773A fb1eb56d-569c-4f11-83d0-8c60ced37856 0174126246 ANEA 2024.2694 …/PV579017… Anguillosyllis dalgleishae sp. nov. NHM_1867 7195bc27-fb46-4f87-8c76-48266394b848 0174126319 ANEA 2024.2695 (holotype) …/PV579018/… Anguillosyllis dalgleishae sp. nov. NHM_1990 d6d4cdd0-e6ab-4e61-b9b0-e2eb3881e64a 0174126304 ANEA 2024.2696 …/PV664892/… Anguillosyllis dalgleishae sp. nov. NHM_1669A b6584f26-950c-4506-b7e0-aec9cd37c46e 0174126257 ANEA 2024.2697 (paratype) …/PV579019/… Anguillosyllis dalgleishae sp. nov. NHM_4729_ ECDS5 9f76d801-e1bb-42d2-830d-0caec6103f72 0174126254 ANEA 2024.2698 …/…/PV579029 Anguillosyllis dalgleishae sp. nov. NHM_4731_ ECDS2 2cb21b0d-bbf1-4c9e-a04e-728c72a9041d 0174126273 ANEA 2024.2699 …/PV579020/… Anguillosyllis villarae sp. nov. NHM_5657 c382ab84-7641-40bb-91db-107aa41c8eee 0174126296 ANEA 2024.2701 (paratype) PV577533/…/… Anguillosyllis villarae sp. nov. NHM_8730 71da1d0f-f4b9-4390-a8de-4c55e8351ad0 0174126248 ANEA 2024.2702 PV577534/…/… Anguillosyllis villarae sp. nov. NHM_8730B 290627ed-657b-4965-a9bd-920e8ca878ce 0174126303 ANEA 2024.2703 PV577535/…/PV579031 Anguillosyllis villarae sp. nov. NHM_8811 aa8735af-ee3a-456f-bc57-888dd874e7fc 0174126322 ANEA 2024.2704 (holotype) PV577536/PV579024/ PV579032 Anguillosyllis villarae sp. nov. NHM_5908 bc633595-9ba5-4320-a0c8-e0022060eac7 0174126247 ANEA 2024.2705 …/PV579025/… European Journal of Taxonomy 1026: 30–64 (2025) 38 Table 1 (continued). SpeciesSpecimen record no. GUID MCf no. NHMUK reg. # GenBank Acc. # COI/16S/18S Anguillosyllis villarae sp. nov. NHM_7689B 2280eace-04fb-430a-aa3f-d2163f629c86 0174126320 ANEA 2024.2706 (paratype) PV577537/…/… Anguillosyllis villarae sp. nov. NHM_9396_ HW18 d38da487-db2d-4274-bc96-ba7af0112e02 0174126278 ANEA 2024.2707 PV577538/…/… Anguillosyllis villarae sp. nov. NHM_10276 82b4921b-0ff9-4337-9bc4-034367e808c5 0174123627 ANEA 2024.2708 PV577539/…/… Anguillosyllis villarae sp. nov. NHM_10374_ CB12 fe6b7444-31bf-400f-9ed1-66530bb53a8c 0174126302 ANEA 2024.2709 PV577540/…/… Anguillosyllis villarae sp. nov. NHM_7227A 45112357-3af9-4c7f-8c93-d014c68f64ca 0174126280 ANEA 2024.2710 …/PV579026/… Anguillosyllis villarae sp. nov. NHM_6940 50527b56-3f4d-430f-929b-fa4d91b1d858 0174126295 ANEA 2024.2711 …/PV579027/… Anguillosyllis villarae sp. nov. NHM_5399 8a50f3cb-93de-4aa6-8792-cac45d2b2137 0174126271 ANEA 2024.2712 …/PV579028/… Anguillosyllis finnelli sp. nov. NHM_5880 654e0cbb-ac72-4aec-93b0-a24302d3e16c 0174126256 ANEA 2024.2713 (paratype) PV664495/…/… Anguillosyllis finnelli sp. nov. NHM_4733_ ECDS4 89b42808-8b28-431e-b4d1-7c7b486289b7 0174126249 ANEA 2024.2714 PV577526/PV579021/… Anguillosyllis finnelli sp. nov. NHM_4741_ ECDS4 c2db9a70-9ccb-4d7e-abbf-4bef0404844c 0174126325 ANEA 2024.2715 …/PV579022/… Anguillosyllis finnelli sp. nov. NHM_8801_ HW03 04898df3-ab82-4b5d-8c82-7f0a5a396eac 0174126279 ANEA 2024.2716 PV577527/…/… Anguillosyllis finnelli sp. nov. NHM_8730A c3b77851-d8d0-4a33-9f2b-2a993391f41d 0174126320 ANEA 2024.2717 (paratype) PV577528/…/… Anguillosyllis finnelli sp. nov. NHM_8783_ HW01 68b5e2d7-8061-4f19-adad-b577c49fb335 0174126255 ANEA 2024.2718 PV577529/…/… Anguillosyllis finnelli sp. nov. NHM_8789_ HW05 8a93a352-604b-420f-b328-930c84d540cf 0174126272 ANEA 2024.2719 PV664496/…/… Anguillosyllis finnelli sp. nov. NHM_093 6d7ef8a1-9fa4-4eec-aca2-f68b1ace677b 0174126258 ANEA 2024.2720 (holotype) PV577530/PV579023/ PV579030 Anguillosyllis finnelli sp. nov. NHM_10602_ GB01 f7d6faae-4c53-4fcd-a168-e55f53d3201c 0174126301 ANEA 2024.2721 PV577531/…/… Anguillosyllis finnelli sp. nov. NHM_10334_ CB3 15c30fcb-cfdb-46c1-9066-f6eb52c4eb09 0174126326 ANEA 2024.2722 PV577532/…/… Anguillosyllis finnelli sp. nov. NHM_10372_ CB06 1cd18a15-4081-482f-b380-418cbe9a20e9 0174126321 ANEA 2024.2723 PV664497/…/… NEAL L. et al., New species of Anguillosyllis (Syllidae, Annelida) from the CCZ 45 chaetigers (Fig. 5C), but developed moving posteriorly, becoming subequal in length to the anterior lobe around chaetiger 6, and slightly exceeding the anterior lobe in size on subsequent chaetigers. Dorsal cirri present only on chaetiger 1, where long, filiform (Figs 3D–F, 4A–B, 5A-insert); absent in other chaetigers. Ventral cirri short and conical with an expanded base, inserted midway along the parapodia (Figs 3H, 5A–B). Several pointed acicula per parapodium visible, with tips non emergent (Fig. 5E, marked by arrow). Each parapodium bearing dense bundles of numerous compound heterogomph chaetae, bundles becoming slightly sparser moving posteriorly, chaetae falcigerous to spiniger-like (Fig. 4F–G). Falcigerous chaetae of chaetigers 1–4 with denticulated shafts, with denticles arranged in irregular horizontal rows (Fig. 4D), from chaetiger 5 with shafts indistinctly denticulated or smooth (Fig. 4E). Blades finely serrated, unidentate decreasing in length dorso-ventrally, ranging from elongate, slender spiniger-like to shorter falcigers (Figs 4F–G, 5D), with blades of the longest spiniger-like chaetae 230–250 µm, and shortest falcigers 25–30 µm; chaetae emerge from semicircular flap that extends from posterior lobe ventrally towards the base of the parapodium. pygidiuM. Conical to rounded; with four appendages; lateral cirri missing, ventromedial often missing, when present long, curled and filiform (Fig. 3I). Reproductive information Three specimens ovigerous; eggs visible through body cavity wall in all specimens between chaetigers 6–10, eggs irregularly shaped, ~ 50 µm in diameter (Figs 3A, 5F). Genetic data Specimens (n = 14) assigned to A. dalgleishae sp. nov. form a clade (Supp. file 3: Fig. S1, Supp. file 4: Fig. S2), with low intraspecific divergence across all sequences (maximum intraspecific p-distance/ K2P 0.5/0.5% for 16S and 1.3/1.3% for COI). Sequences matched with high % identity (99.7–100%) in blastn search and 0–0.3% in both p-distance and K2P to a 16S sequence of an unidentified Anguillosyllis specimen (accession number: MK971075; ID: Anguillosyllis sp. 43 PB voucher 021-BGR-0045) (see Fig. 7) collected from the BGR contract area of the Eastern CCZ, published in Bonifácio et al. (2020). In terms of the nuclear 18S gene, A. dalgleishae was also well defined, differing from other Anguillosyllis sequences by a minimum of five (A. cf. hessleri sp. NHM_552 NHMUK2024.1002, A. capensis ZMH_ Fig. 6. Line drawings of prostomia of new species reported in this paper, with the shapes of median lobes (ML), drawings not to scale. A. Anguillosyllis dalgleishae sp. nov. B. Anguillosyllis finnelli sp. nov. C. Anguillosyllis villarae sp. nov. European Journal of Taxonomy 1026: 30–64 (2025) 46 P25593, A. capensis ZMH_P25594) and a maximum of 16 (A. capensis ZMH_P25588) mutations (1543 bp sequence). Remarks Morphologically, the new species can be distinguished from all other currently known species by the combination of the following characters: body with 10 chaetigers, presence of very large conical dorsal lobes (flaps) in parapodia and presence of dorsal cirri on chaetiger 1 only. Anguillosyllis dalgleishae sp. nov. can be distinguished from seven of the currently known species with 10 chaetigers by the presence of large parapodial dorsal lobes. Such lobes are currently known in only three species, that all possess 11, not 10 chaetigers: A. palpata, A. hampsoni and CCZ species A. truebloodi. Further, SEM confirmed the presence of dorsal cirri on chaetiger 1 only, a character currently confirmed by SEM only in other CCZ specimens assigned to Anguillosyllis cf. hessleri by Drennan et al. (2025). Maciolek (2020) using light microscopy considered such distribution as dorsal cirri “missing” in all but first segments. 0.2 Odontosyllis globulocirrata Anguillosyllis capensis ZMH_P25594 Proceraea picta NHM_1347A Anguillosyllis dalgleishae sp. n. Sphaerosyllis sp. MTA_2006 Anguillosyllis sp. 62_PB Anguillosyllis capensis ZMH_P25587 Anguillosyllis capensis ZMH_P25611_B NHM_93 Anguillosyllis finnelli sp. n. Anguillosyllis capensis ZMH_P25593_A Anguillosyllis cf. hessleri sp. NHM_2095 NHMUK_2024.1000 Syllides convolutus Eulalia viridis Amblyosyllis formosa NHM_8811 Anguillosyllis villarae sp. n. Anguillosyllis capensis ZMH_P25588_A Chrysopetalum debile Nereimyra punctata Anguillosyllis cf. hessleri sp. NHM_1740 NHMUK_2024.1025 Eusyllis blomstrandi Anguillosyllis sp. 244_PB Anguillosyllis cf. hessleri sp. NHM_1797C NHMUK_2024.1034 Erinaceusyllis hartmannschroederae Epigamia noroi Syllis compacta Anguillosyllis cf. hessleri sp. NHM_552 NHMUK_2024.1002 Anguillosyllis sp. 43_PB Perkinsyllis koolalya Anguillosyllis sp. MTA_2011 1/98 1/95 0.99/73 1/98 1/81 0.96/70 1/99 1/100 0.99/63 1/100 1/79/ 0.98/92 0.71/88 1/75 1/98 1/86 1/94 0.95/52 1/99 1/100 1/100 0.99/95 1/96 1/95 0.92/89 Fig. 7. Phylogenetic analysis of Anguillosyllis Day, 1963 using combined Bayesian analysis of three markers, cytochrome oxidase subunit I (COI), 16S RNA and 18S RNA. New species described in this study are highlighted in bold and colour. The tree also includes representatives of the Anguillosyllis cf. hessleri species complex described in Drennan et al. (2025), in addition to nine Anguillosyllis, ten syllid and three non-syllid nereidiform outgroup sequences from Genbank. Support values are given at nodes as Bayesian posterior probability values / maximum likelihood (ML) bootstrap values. NEAL L. et al., New species of Anguillosyllis (Syllidae, Annelida) from the CCZ 47 However, given our observations, it may be the case of true absence in the following 10 chaetigers bearing species: A. taleola, A. sepula and A. elegantissima. Distribution Eastern CCZ: UK-1 and OMS exploration areas, depth ~ 4200 m. Also, BGR area (Bonifácio et al. 2020). Anguillosyllis finnelli sp. nov. urn:lsid:zoobank.org:act:1E961327-01B3-4D90-8227-1C13C8756D03 Figs 6B, 8–12 Diagnosis Body with 11 chaetigers. Prostomium in two parts, with three short antennae. Palps elongated, free to the base. Parapodia with large conical dorsal lobes (flaps). Dorsal cirri absent in chaetiger 2. Heterogomph chaetae unidentate. Etymology The species name is dedicated to Cletus Finnell, Able Seaman on the RV Melville on the October 2013 cruise ‘ABYSSLINE AB01’. Material examined Holotype PACIFIC OCEAN – Eastern Central Pacific, Clarion Clipperton Fracture Zone • 13.79335° N, 116.7030833° W; 4081 m depth; 11 Oct. 2013; A.G. Glover, H. Wiklund, T. Dahlgren and M. Georgieva leg.; USNEL Box Core; specimen GUID: 6d7ef8a1-9fa4-4eec-aca2-f68b1ace677b; field ID NHM_00093; GenBank COI gene: PV577530; 16S gene: PV579023; 18S gene: PV579030; NHMUK ANEA 2024.2720. Fig. 8. Anguillosyllis finnelli sp. nov. A. Paratype (NHMUK ANEA 2024.2717), preserved, in dorsal view, with Shirlastain A residue. B. Preserved specimen (NHMUK ANEA 2024.2719) in dorsal view. Scale bars = 1 mm. European Journal of Taxonomy 1026: 30–64 (2025) 48 Paratypes PACIFIC OCEAN – Eastern Central Pacific, Clarion Clipperton Fracture Zone • 1 spec.; 10.33079203° N, 117.1940202° W; 4290.89 m depth; 1 Jun. 2021; H. Wiklund, R. Drennan, C. Boolukos and G. Bribiesca Contreras leg.; USNEL Box Core; specimen GUID: c3b77851-d8d0-4a33-9f2b2a993391f41d; field ID; NHM_08730A; GenBank COI gene: PV577528; NHMUK ANEA 2024.2717 • 1 spec.; 10.35561637° N, 117.1686897° W; 4280 m depth; 11 Nov. 2020; H. Wiklund, R. Drennan, C. Boolukos and G. Bribiesca Contreras leg.; USNEL Box Core; specimen GUID: 654e0cbb-ac724aec-93b0-a24302d3e16c; field ID NHM_05880; GenBank COI gene: PV664495; NHMUK ANEA 2024.2713. Other material PACIFIC OCEAN – Eastern Central Pacific, Clarion Clipperton Fracture Zone • 1 spec.; 12.36565642° N, 116.7520565° W; 4159.33 m depth; 10 Mar. 2020; A.G. Glover, H. Wiklund, G. Bribiesca Contreras and E. Simon Lledó leg.; USNEL Box Core; specimen GUID: 89b42808-8b28-431e-b4d17c7b486289b7; field ID NHM_04733_ECDS4; GenBank COI gene: PV577526; 16S gene: PV579021; NHMUK ANEA 2024.2714 • 1 spec.; 12.38927437° N, 116.6362959° W; 4179.39 m depth; 11 Mar. 2020; A.G. Glover, H. Wiklund, G. Bribiesca Contreras and E. Simon Lledó leg.; USNEL Box Core; specimen Fig. 9. Anguillosyllis finnelli sp. nov., holotype (NHMUK ANEA 2024.2720) unless stated otherwise; specimen stained with Shirlastain A in images D–G. A. Complete live specimen with 11 chaetigers in ventral view, image taken on board the ship. B. Now posteriorly incomplete preserved specimen in dorsal view, with tissue sampled for DNA. C. Fully extended palps in specimen NHMUK ANEA 2024.2719 in dorsal view. D. Detail of prostomium with outline of the median prostomial lobe traced by a thin line, palps curled ventrally, Shirlastain A faded. E. Detail of club-shaped median antenna (MA) in lateral view. F. Detail of lateral antennae (LA) in dorsal view. G. Tentacular cirrus (TC) in dorsal view. Scale bars = B–C = 500 µm; D = 250 µm. NEAL L. et al., New species of Anguillosyllis (Syllidae, Annelida) from the CCZ 49 GUID: c2db9a70-9ccb-4d7e-abbf-4bef0404844c; field ID NHM_04741_ECDS4; GenBank 16S gene: PV579022; NHMUK ANEA 2024.2715 • 1 spec.; 10.35780083° N, 117.1593114° W; 4284 m depth; 13 Nov. 2020; H. Wiklund, R. Drennan, C. Boolukos and G. Bribiesca Contreras leg.; USNEL Box Core; specimen GUID: 68b5e2d7-8061-4f19-adad-b577c49fb335; field ID NHM_08783_HW01; GenBank COI gene: PV577529; NHMUK ANEA 2024.2718 • 1 spec.; 10.33498329° N, 117.1741855° W; 4286 m depth; 6 Nov. 2020; H. Wiklund, R. Drennan, C. Boolukos and G. Bribiesca Contreras leg.; USNEL Box Core; specimen GUID: 8a93a352-604b-420f-b328-930c84d540cf; field ID NHM_08789_HW05; GenBank COI gene: PV664496; NHMUK ANEA 2024.2719 • 1 spec.; 10.35561637° N, 117.1686897° W; 4280 m depth; 11 Nov. 2020; H. Wiklund, R. Drennan, C. Boolukos and G. Bribiesca Contreras leg.; USNEL Box Core; specimen GUID: 04898df3-ab82-4b5d-8c82-7f0a5a396eac; field ID NHM_08801_HW03; GenBank COI gene: PV577527; NHMUK ANEA 2024.2716 • 1 spec.; 10.333014° N, 117.18551° W; 4281 m depth; 12 Feb. 2022; H. Wiklund, C. Boolukos, E. Stewart and A. Bessell leg.; USNEL Box Core; specimen GUID: 15c30fcb-cfdb-46c1-9066-f6eb52c4eb09; field ID NHM_10334_CB3; GenBank COI gene: PV577532; NHMUK ANEA 2024.2722 • 1 spec.; 10.353342° N, 117.242837° W; 4296 m depth; 19 Nov. 2022; H. Wiklund, C. Boolukos, E. Stewart and A. Bessell leg.; USNEL Box Core; specimen GUID: 1cd18a15-4081-482f-b380-418cbe9a20e9; field ID NHM_10372_CB06; GenBank COI gene: PV664497; NHMUK ANEA 2024.2723 • 1 spec.; 13.7309° N, 126.2041° W; 4704 m depth; 20 Feb. 2023; A.G. Glover, E. Stewart, G. Bribiesca Contreras and E. Simon Lledó leg.; USNEL Box Core; specimen GUID: f7d6faae-4c53-4fcd-a168-e55f53d3201c; field ID NHM_10602_GB01; GenBank COI gene: PV577531; NHMUK ANEA 2024.2721. Description MeasureMents and appearance. Moderately sized species, up to 2 mm in length for 11 chaetigers (Fig. 8A–B). Holotype NHMUK ANEA 2024.2720, now posteriorly incomplete due to tissue sampling Fig. 10. Anguillosyllis finnelli sp. nov., paratype (NHMUK ANEA 2024.2713), SEM micrographs. A. Posteriorly incomplete specimen in dorsal view. B. Anterior end in dorsal view, with detail of prostomium and dorsal cirrophores on chaetigers 1 and 3, showing true absence on chaetiger 2. C. Detail of prostomium and palps in lateral view. D. Detail of attachment of palps to prostomium, showing palps free to the base. E. Bundle of chaetae from anterior parapodium. Scale bars: A = 500 µm; B = 200 µm; C = 100 µm; D–E = 50 µm. European Journal of Taxonomy 1026: 30–64 (2025) 50 for DNA, ~ 1.65 mm long and 0.25 mm wide for 7 chaetigers (Fig. 9A, C); live specimen presented with complete body with 11 chaetigers (Fig. 9A). Paratype NHMUK ANEA 2024.2717, now posteriorly incomplete with 9 chaetigers, 1.8 mm long and 0.3 mm wide at widest point (Fig. 8B). Paratype NHMUK ANEA 2024.2713, SEM specimen on stub, posteriorly incomplete and damaged, ~ 1.55 mm long and 0.25 mm wide for 7 chaetigers (Fig. 10A). Other specimens in variable condition, usually posteriorly incomplete due to fragmentation or tissue sampling for DNA, where complete body with 11 chaetigers. Body somewhat dorsoventrally flattened, tapering slightly from chaetiger 4 anteriorly. Live specimen semi-translucent, without pigmentation (Fig. 9A); fixed specimen opaque, creamy white to pale yellow in ethanol (Figs 8A–B, 9B). prostoMiuM. Oval, wider than long; differentiation of median lobe visible even under light microscopy in holotype (Fig. 9D); median lobe broadly pentagonal, anteriorly with two broad peaks (Figs 6B, 9D). Eyes absent. Prostomium bearing three short, digitiform to club-shaped antennae and two palps (Figs 9E– F, 10A–C). Antennae slightly shorter than the prostomium; median antenna club shaped (Fig. 9E), slightly longer than lateral antennae, and inserted posterio-dorsally on the prostomium; lateral antennae digitiform (Fig. 9F), inserted more anteriorly. Palps ~ 1.5 the length of prostomium, digitiform, thick and distally rounded, free to the base when fully extended (Figs 9C, 10A–D); curled ventrally in holotype, obscuring their true shape (Fig. 9A–B, D). tentacular segMent. Achaetous, bearing two, very short, papilliform tentacular cirri, >⅓ the length of the antennae and inserted laterally (Figs 9G, 10B). Pharyngeal tube extending to chaetiger 3, unarmed; proventricle spanning from chaetigers 3–5, barrel-shaped; number of muscle cell rows mostly obscured by body wall in preserved specimens, best observed in live specimen (Fig. 9A). parapodia. Long, rectangular, and uniramous. Parapodia with distally rounded, large conical dorsal lobe (Figs 10A–B, 11A) and two short papilliform lobes with anterior and posterior lobes of similar Fig. 11. Anguillosyllis finnelli sp. nov., holotype (NHMUK ANEA 2024.2720) stained with Shirlastain A. A. Parapodia with parapodial lobes. B. Detail of parapodial lobes. C. Parapodium with ventral cirrus. D. Compound chaetae from chaetiger 2. E. Compound chaetae from chaetiger 4. Scale bars: B = 25 µm; D–E = 50 µm. NEAL L. et al., New species of Anguillosyllis (Syllidae, Annelida) from the CCZ 51 size (Fig. 11B). Dorsal cirri missing, SEM shows presence of cirrophores on all chaetigers, except for chaetiger 2 where truly absent (Fig. 10A–B). Ventral cirri conical, and short approximately half the length of the antennae, inserted midway to ⅔ along the length of the parapodia moving away from the body (Fig. 11C). At least three acicula per parapodium, two with emergent tips. Each parapodium bearing dense bundles of numerous compound heterogomph chaetae (Fig. 11A), with chaetal bundles becoming somewhat sparser posteriorly. Anterior falcigerous chaetae with denticulated shafts, denticles arranged in irregular horizontal rows (Fig. 12A); other chaetae with smooth shafts and finely serrated, unidentate blades decreasing in length dorso-ventrally, ranging from elongate, slender spiniger-like to shorter falcigers (Figs 11D–E, 12B–C). Blades of the longest spiniger-like chaetae ~ 170 µm, and shortest falcigers ~ 20 µm. Tips of compound chaetae blunt, unidentate, at most gently hooked (Fig. 12B–C). pygidiuM. Damaged; pygidial appendages missing. Genetic data Specimens (n = 11) assigned to A. finnelli sp. nov. form a clade (Supp. file 3: Fig. S1, Supp. file 4: Fig. S2), with low intraspecific divergence across all sequences (maximum intraspecific p-distance/K2P distance 0.5/0.5% for 16S and 1.9/1.9% for COI). Sequences matched with high % identity (99–100%) in blastn search and by intraspecific distance (maximum p-distance/K2P 1.8/1.8%) to a COI sequence of an unidentified Anguillosyllis specimen (accession number: MK971075; ID: Anguillosyllis sp. 244_PB voucher 088-IOM-0246) (Fig. 7) collected from the IOM contract area of the Eastern CCZ, published in Bonifácio et al. (2020). In combined analyses (Fig. 7), this species is close to a polytomy consisting of Anguillosyllis villarae sp. nov. and GenBank sequences identified as Anguillosyllis sp. MTA_2011 from Costa Rica (accession numbers 18S:JF903571; 16S: JF903680; COI: JF903756) published in Aguado et al. (2012). However, minimum interspecific p-distance/K2P of 14.4/16% 16S, and 16.1/18.3% COI were observed between these species and A. finnelli, while in an alignment of nuclear 18S (1630 bp), Fig. 12. Anguillosyllis finnelli sp. nov., paratype (NHMUK ANEA 2024.2713), SEM micrographs. A. Falcigerous chaetae of chaetiger 3 with denticulated ornamented shafts. B. Falcigerous chaetae from chaetiger 1. C. Chaeta from chaetiger 2. Scale bars: A = 5 µm; B = 10 µm; C = 20 µm. European Journal of Taxonomy 1026: 30–64 (2025) 52 A. finnelli differed by two and four mutations from A. villarae sp. nov and Anguillosyllis sp. MTA_2011 respectively. Remarks The new species belongs to the group of Anguillosyllis with 11 chaetigers, well-developed parapodial lobes and palps free to a large extent, although this character is difficult to establish when palps are curled up (Neal pers. obs.). Of the known species, Anguillosyllis truebloodi also shares such characters, and also the CCZ distribution (DOMES site, Wilson 2017). However, the new species can be easily distinguished by the true absence of dorsal cirri on chaetiger 2 as revealed by SEM (Fig. 10B), which is present in A. truebloodi. Maciolek (2020) also reported palps as fused halfway to the base in A. truebloodi, whilst these are free to the base in the new species (Fig. 10A, D), although from certain angles, particularly where bent, the palps may appear fused. Another similar species is Anguillosyllis palpata with type locality in the Drake Passage in relatively shallow depths of 384–494 m, which has since been widely reported worldwide, including abyssal depths (Maciolek 2020). Morphological variation in specimens identified as A. palpata has been reported by Maciolek (2020), but in the absence of molecular data, species differentiation is difficult. The species newly reported here differs from A. palpata in the form of the chaetae, which are distinctly hooked in A. palpata, but not in the new species, in which they are at most gently hooked (Figs 11D, 12B–C), absence of large postchaetal lobes and true absence of dorsal cirri on chaetiger 2 (Fig. 10B). Distribution Eastern CCZ: NORI-D exploration area, depth ~ 4300 m; UK-1 exploration area, depth ~ 4200 m; OMCO site, depth ~ 4700 m. Also, IOM area (Bonifácio et al. 2020). Anguillosyllis villarae sp. nov. urn:lsid:zoobank.org:act:E0177D9E-D221-48C7-A76C-2804FD4C469C Figs 6C, 13–16 Diagnosis Body with 10 chaetigers. Prostomium in two parts, with three short antennae. Palps elongated, free to the base. Parapodia with large conical dorsal lobes (flaps). Heterogomph chaetae unidentate with some tips hooked or with tips bidentate; some chaetae with wide strap-like blades. Etymology The species name is dedicated to Lucía Villar Muñoz a member of the science party on expeditions C5a, C5d, C7a, and C7b to the NORI-D area, particularly for her work slicing and sieving boxcore samples. Material examined Holotype PACIFIC OCEAN – Eastern Central Pacific, Clarion Clipperton Fracture Zone • 10.354901° N, 117.220794° W; 4273.8 m depth; 23 Nov. 2020; H. Wiklund, R. Drennan, C. Boolukos and G. Bribiesca Contreras leg.; USNEL Box Core; specimen GUID: aa8735af-ee3a-456f-bc57-888dd874e7fc; field ID; NHM_08811; GenBank COI gene: PV577536; 16S gene: PV579024; 18S gene: PV579032; NHMUK ANEA 2024.2704. Paratypes PACIFIC OCEAN – Eastern Central Pacific, Clarion Clipperton Fracture Zone • 1 spec.; 10.32909125° N, 117.1971482° W; 4281 m depth; 9 Nov. 2020; H. Wiklund, R. Drennan, C. Boolukos and G. Bribiesca Contreras leg.; USNEL Box Core; specimen GUID: c382ab84-7641-40bb-91db- NEAL L. et al., New species of Anguillosyllis (Syllidae, Annelida) from the CCZ 53 107aa41c8eee; field ID NHM_05657; GenBank COI gene: PV577533; NHMUK ANEA 2024.2701 • 1 spec.; 10.34811115° N, 117.1706608° W; 4282.6 m depth; 17 May. 2021; H. Wiklund, R. Drennan, C. Boolukos and G. Bribiesca Contreras leg.; USNEL Box Core; specimen GUID: 2280eace-04fb430a-aa3f-d2163f629c86; field ID NHM_07689B; GenBank COI gene: PV577537; NHMUK ANEA 2024.2706. Other material PACIFIC OCEAN – Eastern Central Pacific, Clarion Clipperton Fracture Zone • 1 spec.; 10.33498329° N, 117.1741855° W; 4286 m depth; 6 Nov. 2020; H. Wiklund, R. Drennan, C. Boolukos and G. Bribiesca Contreras leg.; USNEL Box Core; specimen GUID: 8a50f3cb-93de-4aa6-8792cac45d2b2137; field ID NHM_05399; GenBank 16S gene: PV579028; NHMUK ANEA 2024.2712 • 1 spec.; 10.3861134° N, 117.1309018° W; 4308 m depth; 12 Nov. 2020; H. Wiklund, R. Drennan, C. Boolukos and G. Bribiesca Contreras leg.; USNEL Box Core; specimen GUID: bc633595-9ba54320-a0c8-e0022060eac7; field ID NHM_05908; GenBank 16S gene: PV579025; NHMUK ANEA 2024.2705 • 1 spec.; 10.33426964° N, 117.1901234° W; 4287.72 m depth; 12 May. 2021; H. Wiklund, C. Boolukos, M. Rabone and G. Bribiesca-Contreras leg.; USNEL Box Core; specimen GUID: 50527b563f4d-430f-929b-fa4d91b1d858; field ID NHM_06940; GenBank 16S gene: PV579027; NHMUK ANEA 2024.2711 • 1 spec.; 10.37726533° N, 117.1558078° W; 4302.03 m depth; 14 May. 2021; H. Wiklund, C. Boolukos, M. Rabone and G. Bribiesca Contreras leg.; USNEL Box Core; specimen GUID: 45112357-3af9-4c7f-8c93-d014c68f64ca; field ID NHM_07227A; GenBank 16S gene: PV579026; NHMUK ANEA 2024.2710 • 1 spec.; 10.33079203° N, 117.1940202° W; 4290.89 m depth; 1 Jun. 2021; H. Wiklund, R. Drennan, C. Boolukos and G. Bribiesca Contreras leg.; USNEL Box Core; specimen GUID: 71da1d0f-f4b9-4390-a8de-4c55e8351ad0; field ID NHM_08730; GenBank COI gene: PV577534; NHMUK ANEA 2024.2702 • 1 spec.; 10.33079203° N, 117.1940202° W; 4290.89 m depth; 1 Jun. 2021; H. Wiklund, R. Drennan, C. Boolukos and G. Bribiesca Contreras leg.; USNEL Box Core; specimen GUID: 290627ed-657b-4965-a9bd-920e8ca878ce; field ID NHM_08730B; GenBank COI gene: PV577535; 18S gene: PV579031; NHMUK ANEA 2024.2703 • 1 spec.; 10.332533° N, 117.187352° W; 4281 m depth; 24 Aug. 2022; H. Wiklund, C. Boolukos and E. Stewart leg.; USNEL Box Core; specimen GUID: d38da487-db2d-4274-bc96-ba7af0112e02; field ID NHM_09396_HW18; GenBank COI gene: PV577538; NHMUK ANEA 2024.2707 • 1 spec.; 10.334243° N, 117.185992° W; 4279 m depth; 12 Mar. 2022; H. Wiklund, C. Boolukos, E. Stewart and A. Bessell leg.; USNEL Box Core; specimen GUID: 82b4921b-0ff9-4337-9bc4-034367e808c5; field ID NHM_10276; GenBank COI gene: PV577539; NHMUK ANEA 2024.2708 • 1 spec.; 10.334296° N, 117.17708° W; 4282 m depth; 21 Nov. 2022; H. Wiklund, C. Boolukos, E. Stewart and A. Bessell leg.; USNEL Box Core; specimen GUID: fe6b7444-31bf-400f-9ed1-66530bb53a8c; field ID NHM_10374_CB12 ; GenBank COI gene: PV577540; NHMUK ANEA 2024.2709. Description MeasureMents and appearance. Moderately sized species, up to 2 mm in length for 10 chaetigers (Fig. 13A–C). Holotype NHMUK ANEA 2024.2704, posteriorly complete, 1.6 mm long and 0.25 mm at widest point for 10 chaetigers; only left lateral antenna remains attached, pygidium with cirri missing (Fig. 13A–B). Paratype NHMUK ANEA 2024.2701, live specimen translucent with 10 chaetigers (Fig. 13C), now as SEM specimen on stub, posteriorly incomplete, ~ 0.8 mm long and 0. 25 mm wide at widest point for 5 chaetigers, left lateral antenna missing (Fig. 14A). Paratype NHMUK ANEA 2024.2706, specimen with 10 chaetigers, with pygidium removed for tissue sampling for DNA analysis, rest of the body well preserved, ~ 1.3 mm long 0.25 mm wide. Other specimens in variable condition, usually posteriorly incomplete due to preservation or tissue sampling for DNA. Body somewhat dorsoventrally flattened. Fixed specimen opaque, creamy white in ethanol (Fig. 13 A–B). European Journal of Taxonomy 1026: 30–64 (2025) 54 Fig. 13. Anguillosyllis villarae sp. nov. A–B. Holotype (NHMUK ANEA 2024.2704). A. 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Marine Biodiversity 47 (2): 323–347. https://doi.org/10.1007/s12526-016-0609-8 Printed versions of all papers are deposited in the libraries of three of the institutes that are members of the EJT consortium: Muséum national dʼHistoire naturelle, Paris, France; Royal Museum for Central Africa, Tervuren, Belgium; Royal Belgian Institute of Natural Sciences, Brussels, Belgium. The other members of the consortium are: Meise Botanic Garden, Meise, Belgium; Natural History Museum of Denmark, Copenhagen, Denmark; Naturalis Biodiversity Center, Leiden, the Netherlands; Museo Nacional de Ciencias Naturales-CSIC, Madrid, Spain; Leibniz Institute for the Analysis of Biodiversity Change, Bonn – Hamburg, Germany; National Museum of the Czech Republic, Prague, Czech Republic; The Steinhardt Museum of Natural History, Tel Aviv, Israël. Supplementary files Supp. file 1. Table S1. List of sequences from GenBank used in phylogenetic analyses. https://doi.org/10.5852/ejt.2025.1026.3105.13849 Supp. file 2. Table S2. GenBank numbers for phylogenetic analysis data downloaded from GenBank. https://doi.org/10.5852/ejt.2025.1026.3105.13851 European Journal of Taxonomy 1026: 30–64 (2025) 64 Supp. file 3. Fig. S1. Phylogenetic analysis of Anguillosyllis Day, 1963 using the 16S RNA barcode marker. New species described in this study are highlighted in bold and colour. The tree also includes representatives of the Anguillosyllis cf. hessleri species complex described in Drennan et al. (2025), in addition to nine Anguillosyllis, ten syllid and three non-syllid nereidiform outgroup sequences from GenBank. Support values are given at nodes as maximum likelihood (ML) bootstrap values. https://doi.org/10.5852/ejt.2025.1026.3105.13853 Supp. file 4. Fig. S2. Phylogenetic analysis of Anguillosyllis Day, 1963 using the Cytochrome Oxidase Subunit I (COI) barcode marker. New species described in this study are highlighted in bold and colour. The tree also includes representatives of the Anguillosyllis cf. hessleri species complex described in Drennan et al. (2025), in addition to nine Anguillosyllis, ten syllid and three non-syllid nereidiform outgroup sequences from GenBank. Support values are given at nodes as maximum likelihood (ML) bootstrap values. https://doi.org/10.5852/ejt.2025.1026.3105.13855