New findings and two new species of the genus Colossendeis Jarzynsky, 1870 (Pycnogonida, Colossendeidae), with a morphometric analysis for species from the Southern Ocean

ORIGINAL PAPER New findings and two new species of the genus Colossendeis Jarzynsky, 1870 (Pycnogonida, Colossendeidae), with a morphometric analysis for species from the Southern Ocean Esperanza Cano-Sánchez 1 &Pablo J. López-González 1 Received: 16 May 2022 /Revised: 22 November 2022 /Accepted: 25 November 2022 #The Author(s) 2022 Abstract In this paper, specimens belonging to the pycnogonid genus Colossendeis Jarzynsky, 1870 collected during the Antarctic Polarstern XXIII/8 cruise (November 23, 2006, to January 30, 2007) were studied. In this collection, the following thirteen species have been identified, two of them being proposed as new species: Colossendeis frigida Hodgson, 1907,C. megalonyx Hoek, 1881,C. wilsoni Calman, 1915,C. engirmatica Turpaeva, 1974,C. arundorostris Fry & Hedgpeth, 1969,C. scotti Calman, 1915,C. lilliei Calman, 1915,C. drakei Calman, 1915,C. glacialis Hodgson, 1907,C. australis Hodgson, 1907, C. tortipalpis Gordon, 1932,C. pseudofrigida sp. nov., and C. bamberi sp. nov. All species are diagnosed and their taxonomic status discussed. C. frigida,C. engirmatica,andC. arundorostris extend their known depth range. C. arundorostris has been found for the first time outside the Ross Sea. The finding of C. engirmatica represents the first record after its original description. The new species are described, illustrated, and compared with their closest congeners. Finally, we carried out a cluster analysis (Bray-Curtis similarity index) based on a data-matrix of 49 Antarctic and Sub-Antarctic Colossendeis species and 26 morphological characters. Keywords Antarctica .Pycnogonids .Sea spider .Sub-Antarctica .Taxonomy Introduction The genus Colossendeis Jarynsky, 1870 has a relatively high number of species in Antarctic and Sub-Antarctic waters. Munilla and Soler-Membrives (2009) reported 37 species for this area, but the current number of Colossendeis species has to be regarded with caution. Most of these species have been described using a very small (if not a single) number of specimens and solely based on morphological characters. In this genus, there are several cases in which no clear species delimitations have been defined, mainly due to the lack of information about the variability of key morphological characters and the existence of similar morphological species. This situation has generated several controversial species and synonyms, such as C. robusta Hoek, 1881. This is the case of C. lilliei Calman, 1915, which has been considered a synonym of C. robusta by Child (1995), Munilla and Soler-Membrives (2009), and Bamber et al. (2022). However, this last synonym is contested by other authors (e.g. Cano-Sánchez and López- González 2007; Turpaeva and Rajsky 2013). Indirectly, Krabbe et al. (2010) corroborated the latter interpretation in their study on the phylogenetic position of C. megalonyx Hoek, 1881 within the genus Colossendeis. Another controversial taxonomic status is that of C. glacialis Hodgson, 1907 considered a junior synonym of C. robusta by some authors (Fry and Hedgpeth 1969;Child1995) but considered a separate species by others (Pushkin 1993; Stiboy-Risch 1993; Cano-Sánchez and López-González 2007; Munilla and Soler-Membrives 2009; Turpaeva and Rajsky 2013; Bamber et al. 2022). Recently molecular or combined molecularmorphological studies have confirmed that C. robusta and C. glacialis must be considered distinct species (Dietz et al. 2015a; Dietz et al. 2019). This article is registered in ZooBank under http://zoobank.org/ 8EF16B65-D964-4215-BDDF-2B68F5C69A20. Communicated by E. Macpherson *Esperanza Cano-Sánchez [email protected] 1 Biodiversidad y Ecología Acuática, Departamento de Zoología, Facultad de Biología, Universidad de Sevilla, Reina Mercedes, 6, 41012 Sevilla, Spain https://doi.org/10.1007/s12526-022-01328-7 / Published online: 29 March 2023 Marine Biodiversity (2023) 53:24 Currently, the most controversial taxonomic case within the genus Colossendeis is C. megalonyx, which is considered a complex species. Colossendeis megalonyx,C. frigida Hodgson, 1907,C. rugosa Hodgson, 1907,andC. scoresbii Gordon, 1932 are morphologically similar, and several authors expressed doubts about the separation of these species (Loman 1923; Gordon 1932;Fage1956;Stock1963). Fry and Hedgpeth (1969) considered these species as junior synonyms of C. megalonyx and proposed a set of four subspecies. Furthermore, subsequent authors have described new morphologically similar species to C. megalonyx (see Pushkin 1993; Child 1995; Turpaeva 2008; Turpaeva and Rajsky 2013)or considered that some of them presented enough morphological differences to be accepted as a single species, which is the case of C. scoresbii (Pushkin 1993;Child1995), increasing the controversy about the status of C. megalonyx as a species complex. In addition, molecular studies have revealed several cryptic lineages within the C. meglonyx complex, supporting the hypothesis that there are several unrecognized species within C. megalonyx (Krabbe et al. 2010; Dietz et al. 2013,2015b, 2019; Dömel et al. 2020). Only C. scoresbii has been confirmed to be separated from C. megalonyx (Krabbe et al. 2010; Dietz et al. 2019). More recently, a combined molecular and morphological study has revealed a high morphological variation within the clades, hindering the possible differentiation of lineages in this C. megalonyx species complex (Dömel et al. 2020). Unfortunately, these clades have not been morphologically characterized and consequently have not been assigned to any Colossendeis binomen. The single exception is the clade that Krabbe et al. (2010)assignedtoC. orcadense Hodgson, 1908 based on the absence of eyes. Krabbe et al. (2010) and Dietz et al. (2015b,2019) noted that a taxonomic review of the C. megalonyx group is necessary. Another clade in these papers in need of taxonomic revision involved C. bouvetensis Dietz & Leese in Dietz et al. 2015a,C. lilliei, and C. wilsoni Calman, 1915, which are a set of species with many similar morphologic characters (see Dietz et al. 2019). This paper uses data from a number of Colossendeis species that were collected during the Polarstern cruise XXIII/8 (November 23, 2006–January 30, 2007). Each Colossendeis species is diagnosed, mainly using ratios between morphometric measurements of characters, and two new species are fully illustrated and described. The observed variability of some characters in comparison to previously published studies is briefly discussed. Finally, a qualitative cluster analysis using measurements and ratios between morphological characters of Colossendeis Antarctic and Sub-Antarctic species is presented. Material and methods A total of 338 adult specimens of Colossendeis were studied. They were collected at the South Shetlands Islands, Elephant Island, Bransfield Strait, Joinville Island, Dundee Island (Paulet Island) and Larsen B, during the Antarctic Polarstern cruise XXIII/8. Samples were collected using a bottom trawl and a small Agassiz trawl (Gutt 2008). Stations data are detailed in Table 1. The specimens were fixed in 10% buffered formalin and then transferred to 70% ethanol. The taxonomic literature used for the identification of the present specimens included the most important works carried out in the last century on the fauna of Antarctic pycnogonids (e.g. Calman 1915; Gordon 1932,1938,1944; Fry and Hedgpeth 1969; Pushkin 1993;Child1995; among others). The list of synonyms and references for each identified Colessendeis species can be found in Fry and Hedgpeth (1969), Pushkin (1993), Child (1995), and Munilla and Soler-Membrives (2009). Additional information is referenced in the remarks section after the diagnosis section for each identified species. Taking into consideration the absence of knowledge on phylogenetic weight of morphological features, a cluster analysis including all described Colossendeis species in the Southern Ocean (SO, Antarctic and SubAntarctic waters) and the Colossendeis specimens collected during the present cruise was carried out to detect trends in the behaviour of these variables, as well as to explore intra- and inter-specific variability, but is not necessarily looking for potential phylogenetic implications. A set of traditional characters used in taxonomic studies of Colossendeis species was measured in each identified specimen, summarizing a total of 26 characters (SMTable 1). According to Cano-Sánchez and López-González (2016), the palp in Colossendeis species is 8- or 9-articled. The criteria used in the measurement of the different structures follow Fry and Hedgpeth (1969). When necessary, this kind of morphological information (as accurate as possible) was also obtained from original descriptions and illustrations of the type material of the different SO Colossendeis species. PRIMER v6 software (Primer-E Ltd., Plymouth, UK) was used to perform a cluster analysis using a similarity matrix obtained by applying the Bray-Curtis similarity index to a nontransformed data-matrix and group average classification algorithm. The examined specimens have been deposited at the Museu de Zoologia de Barcelona, Spain (MZB), and at the collection of the research group Biodiversidad y Ecología Acuática (BECA) at the University of Seville, Spain. Results Thirteen species were identified from the 338 adult specimens collected during the ANT XX111/8 cruise. Of these 13 species, two were new species and are described below. The cluster analysis for Antarctic and Sub-Antarctic Colossendeis materials showed distinct groupings (nominal species) with high similarity among them (Fig. 1). In all 24 Page 2 of 16 Marine Biodiversity (2023) 53:24 Table 1 Sampling data stations of the ANT XXIII/8 cruise [EWS Eastern Weddell Sea; EI: Elephant Island; SSI: South Shetland Islands; JI Joinville Island; BS Bransfield Strait; B-South Larsen B (core-station South); B-West Larsen B (core-station West); DI Dundee Island (Paulet Island)] Area Station Date Latitude S Longitude W Depth (m) Gear EWS 603-5 07-12-2006 70°30.99'S 08°48.08'W 297.4–273.5 Agassiz trawl EI 605-1 19-12-2006 61°20.35'S 55°29.16'W 145.8–151.3 Bottom trawl EI 605-2 19-12-2006 61°20.19'S 55°31.92'W 133.9–150.1 Bottom trawl EI 605-3 20-12-2006 61°20.33'S 55°31.53'W 137.4–154.1 Agassiz trawl EI 605-5 20-12-2006 61°20.27'S 55°30.92'W 152.2–153.4 Agassiz trawl EI 606-1 20-12-2006 61°15.58'S 54°51.95'W 130.9–173.8 Bottom trawl EI 608-1 20-12-2006 61°11.34'S 54°43.17'W 284.2–293.0 Bottom trawl EI 609-1 20-12-2006 61°11.13'S 54°35.39'W 355.2–279.5 Bottom trawl EI 610-1 21-12-2006 60°58.59'S 55°08.39'W 286.9–311.7 Bottom trawl EI 613-1 21-12-2006 60°55.99'S 55°28.53'W 112.5–157.1 Bottom trawl EI 614-1 21-12-2006 60°52.52'S 55°29.21'W 244.5–250.0 Bottom trawl EI 614-3 21-12-2006 60°52.37'S 55°29.80'W 248.0–258.6 Agassiz trawl EI 616-1 22-12-2006 60°49.81'S 55°36.76'W 483.9–486.6 Bottom trawl EI 617-1 22-12-2006 60°54.09'S 55°39.29'W 151.2–176.2 Bottom trawl EI 618-1 22-12-2006 60°58.42'S 55°46.31'W 147.5–173.7 Bottom trawl EI 619-1 22-12-2006 60°58.26'S 55°47.09'W 200.5–199.9 Bottom trawl EI 621-1 23-12-2006 60°59.31'S 55°50.20'W 164.9–196.6 Bottom trawl EI 622-1 23-12-2006 60°56.70'S 55°52.71'W 218.4–307.0 Bottom trawl EI 623-1 23-12-2006 60°58.00'S 55°54.63'W 214.0–209.3 Bottom trawl EI 624-1 23-12-2006 61°00.33'S 55°51.03'W 151.3–186.1 Bottom trawl EI 626-1 24-12-2006 60°58.70'S 55°49.68'W 164.2–241.3 Bottom trawl EI 628-1 24-12-2006 61°02.28'S 55°45.61'W 119.2–159.5 Bottom trawl EI 629-1 24-12-2006 61°00.39'S 55°46.30'W 162.0–190.7 Bottom trawl EI 630-1 25-12-2006 61°02.95'S 55°48.18'W 115.0–123.8 Bottom trawl EI 632-1 25-12-2006 60°59.36'S 55°49.22'W 144.5–157.9 Bottom trawl EI 633-1 25-12-2006 61°00.25'S 55°53.11'W 168.9–212.8 Bottom trawl EI 638-1 26-12-2006 61°09.72'S 55°59.80'W 148.6–169.9 Bottom trawl EI 639-1 26-12-2006 61°10.27'S 55°56.52'W 127.5–126.8 Bottom trawl EI 641-1 26-12-2006 61°04.72'S 55°51.30'W 125.4–143.2 Bottom trawl EI 642-1 26-12-2006 61°04.38'S 55°59.81'W 253.6–254.4 Agassiz trawl EI 646-1 27-12-2006 61°00.79'S 55°58.23'W 276.9–314.9 Bottom trawl EI 647-1 27-12-2006 61°00.35'S 55°58.17'W 281.7–287.7 Bottom trawl EI 648-1 27-12-2006 61°04.70'S 56°01.30'W 241.0–265.0 Bottom trawl EI 651-1 28-12-2006 61°17.39'S 56°01.68'W 290.1–321.3 Bottom trawl EI 652-1 28-12-2006 61°25.87'S 56°07.10'W 280.6–304.6 Bottom trawl EI 653-1 28-12-2006 61°19.59'S 56°00.24'W 343.5–355.6 Bottom trawl EI 654-1 28-12-2006 61°22.01'S 56°00.95'W 352.6–356.2 Bottom trawl EI 654-3 28-12-2006 61°21.52'S 56°02.28'W 351.4–355.0 Agassiz trawl EI 654-6 29-12-2006 61°22.80'S 56°03.84'W 340.5–342.3 Agassiz trawl EI 655-1 29-12-2006 61°07.11'S 55°42.39'W 62.0–82.9 Bottom trawl EI 656-1 29-12-2006 61°10.62'S 55°41.45'W 89.2–98.4 Bottom trawl EI 657-1 29-12-2006 61°14.28'S 55°48.96'W 132.8–145.1 Bottom trawl EI 658-1 29-12-2006 61°15.79'S 55°37.48'W 102.0–106.5 Bottom trawl EI 659-1 29-12-2006 61°16.89'S 55°42.71'W 136.6–185.3 Bottom trawl SSI 660-1 30-12-2006 61°50.40'S 57°20.28'W 277.4–282.9 Bottom trawl SSI 661-2 30-12-2006 61°39.29'S 57°02.89'W 466.0–467.2 Bottom trawl SSI 662-1 30-12-2006 61°35.91'S 57°17.04'W 425.4–431.8 Bottom trawl SSI 663-1 30-12-2006 61°38.18'S 57°33.17'W 432.0–434.0 Bottom trawl Page 3 of 16 24Marine Biodiversity (2023) 53:24 species the characters used in the analysis do not show sexual dimorphism (SMFig. 1). For the species Colossendeis scotti Calman, 1915, C. wilsoni Calman, 1915,C. lilliei,C. drakei Calman, 1915, C. glacialis,C. australis Hodgson, 1907,C. tortipalpis Gordon, 1932,andC. engirmatica Turpaeva, 1974, the newly collected specimens agree overall with type material features and helped to better define intra-species variability forming distinct groupings. Newly collected five species detected in the largest species aggregation corresponded to the three species of “megalonyx complex,”C. arundorostris Fry & Hedgpeth, 1969,C. megalonyx, and C. frigida and the two new species, C. pseudofrigida sp. nov., C. bamberi sp. nov. The number of individuals per species in the newly collected specimens varies greatly (Fig. 1). The most abundant species was C. frigida with 188 specimens, followed by C. megalonyx with 32 specimens, and the minimum was only 1specimenofC. wilsoni. Three species extended their known depth range (C. frigida,C. engirmatica, and C. arundorostris), and C. arundorostris was found for the first time outside the Ross Sea (Table 2). Taxonomy Family Colossendeidae Hoek, 1881 Genus Colossendeis Jarzynsky, 1870 Colossendeis arundorostris Fry & Hedgpeth, 1969 Material examined See Tables 1and 2and SMTable 3. Diagnosis Proboscis length at least 1.8 times longer than trunk. Second and third lateral processes separated by at least half their own diameter. Palp 9-articled, ratio 6 th /7 th palp article length greater than 6.8; ratio 7 th /8 th palp article less than 0.3; ratio length/ width of 7 th palp article subequal or less than 1. Oviger terminal article non-subchelate. Femur longest of the three longest leg articles; ratio femur/propodus length less than 3.5. Remarks Colossendeis arundorostris was described by Fry and Hedgpeth (1969) as a subspecies of C. megalonyx,and followed by some authors (Turpaeva 1974;Turpaevaand Rajsky 2013), while Child (1995) and Bamber et al. (2022) simply consider it as a junior synonym of C. megalonyx. However, other authors (Pushkin 1993; Munilla and Soler- Membrives 2009)considerC. arundorostris as a valid separate species. The C. arundorostris specimens (holotype plus our material) is within a group distinct from the grouping which includes C. megalonyx specimens (holotype plus our material) (Fig. 1). Colossendeis arundorostris is grouped with C. rugosa,C. arcanus Turpaeva, 2008 and C. bamberi sp. nov. Table 1 (continued) Area Station Date Latitude S Longitude W Depth (m) Gear SSI 664-1 30-12-2006 61°38.86'S 57°48.04'W 336–337.1 Bottom trawl SSI 666-1 31-12-2006 61°40.40'S 58°51.30'W 370.5–406.7 Bottom trawl SSI 668-1 31-12-2006 61°49.32'S 58°34.74'W 151.6–193.0 Bottom trawl SSI 669-1 31-12-2006 61°49.97'S 58°41.30'W 191.9–208.2 Bottom trawl SSI 670-1 01-01-2007 61°59.98'S 59°14.78'W 130.7–144.3 Bottom trawl SSI 672-1 01-01-2007 62°06.70'S 59°28.79'W 94.9–107.5 Bottom trawl SSI 674-1 01-01-2007 61°59.10'S 59°55.57'W 286.3–318.1 Bottom trawl SSI 677-1 02-01-2007 62°10.70'S 60°32.79'W 200.2–205.4 Bottom trawl SSI 681-1 03-01-2007 62°29.27'S 61°24.79'W 122.3–149.6 Bottom trawl SSI 682-1 03-01-2007 62°34.83'S 61°49.76'W 176.3–186.1 Bottom trawl JI 685-1 04-01-2007 62°34.61'S 55°39.38'W 159.2–166.4 Bottom trawl JI 687-1 04-01-2007 62°35.19'S 54°45.99'W 257.3–263.0 Bottom trawl JI 689-1 04-01-2007 62°27.28'S 55°18.23'W 224.4–229.2 Bottom trawl JI 691-1 05-01-2007 62°21.36'S 55°18.94'W 306.5–314.0 Bottom trawl JI 693-1 05-01-2007 62°25.84'S 55°35.07'W 243.0–290.5 Bottom trawl BS 697-1 06-01-2007 63°13.85'S 59°06.30'W 329.1–407.9 Bottom trawl B_South 700-2 11-01-2007 65°55.07'S 60°20.15'W 441.9–445.2 Bottom trawl B_West 710-5 16-01-2007 65°32.86'S 61°38.33'W 238.2–243.0 Agassiz trawl DI 728-2 24-01-2007 63°42.63'S 56°01.63'W 292.8–297.9 Agassiz trawl 24 Page 4 of 16 Marine Biodiversity (2023) 53:24 Fry and Hedgpeth (1969)proposedC. arundorostris as a new subspecies (C. megalonyx arundorostris) based on the presence of "trunk, proboscis, and appendages extremely slim and attenuated". Our study adds additional characters that can be used to identify C. arundorostris; the relative proportion between the length of the 6 th and 7 th palp article (ratio greater than 6.8) and that of the 7 th and 8 th palp article (ratio subequal or less than 0.4) (see also Table 3). Colossendeis australis Hodgson, 1907 Material examined See Tables 1and 2and SMTable 3. Diagnosis Proboscis length longer than trunk, sloping downward, widely inflated from narrow base. Second and Fig. 1 Cluster analysis of Colossendeis species in the Southern Ocean (Representative Holotype specimens and Holotype specimens plus studied specimens) (N, number of examined specimens) Page 5 of 16 24Marine Biodiversity (2023) 53:24 third lateral processes separated by at least half their own diameter. Palps 9-articled, 7 th and 8 th articles subequal, and shorter than 9 th article length. Oviger terminal article subchelate. Legs with a femur/propodus length ratio greater than 2.5. Remarks The specimens of C. australis examined in this study agree with the original description (Hodgson 1907)and subsequent authors (Bouvier 1913;Calman1915;Fryand Hedgpeth 1969; Pushkin 1993;Child1995; Cano-Sánchez Table 2 Sampling data for the examined specimens of Colossendeis species Species (n° specimens) Area Bathymetric range (m) ANT XXIII/8 stations C. megalonyx (32) EI; SSI; BS 102.0–431.8 (100–720) 605-1; 605-2; 605-5; 608-1; 614-3; 617-1; 618-1; 621-1; 624-1; 626-1; 628-1; 629-1; 630-1; 632-1; 633-1; 657-1; 658-1; 662-1; 668-1; 670-1; 697-1 C. frigida (188) EWS; EI; SSI; JI 62.0–486.6 a (3–380) 603-5; 605-1; 608-1; 610-1; 613-1; 614-1; 614-3; 616-1; 617-1; 618-1; 619-1; 621-1; 622-1; 623-1; 624-1; 626-1; 628-1; 629-1; 630-1; 632-1; 633-1; 638-1; 639-1; 641-1; 646-1; 647-1; 648-1; 651-1; 652-1; 653-1; 654-1; 654-3; 655-1; 656-1; 657-1; 658-1; 659-1; 661-2; 662-1; 663-1; 687-1; 691-1; 693-1 C. scotti (28) EI; SSI; JI 112.5–321.3 (32–352) 605-1; 605-2; 605-3; 605-5; 606-1; 608-1; 613-1; 614-3; 626-1; 629-1; 630-1; 648-1; 651-1; 659-1; 670-1; 681-1; 687-1; 693-1 C. drakei (14) EI; SSI; JI; B West 130.7–406.7 (3–3000) 605-1; 609-1; 623-1;642-1; 651-1; 666-1; 668-1; 670-1; 677-1; 693-1; 710-5 C. australis (18) EI; SSI; JI; DI 145.8–486.6 (15–3935) 605-1;614-1;614-3;616-1;652-1;654-6;662-1;668-1;669-1;728-2 C. bamberi sp. nov. (19) EI; SSI; JI; B South 112.5–486.6 605-1;613-1;616-1;652-1;654-1;654-3;654-6;661-2;664-1;668-1; 674-1; 677-1; 682-1; 687-1;700-2 C. engirmatica (7) EI; SSI 145.8–434.0 a (315–435) 605-1; 654-1; 662-1; 663-1 C. glacialis (18) EI; SSI; JI; B South 89.2–486.6 (3–924) 605-1; 605-2; 614-3; 616-1; 638-1; 651-1; 653-1; 656-1; 672-1; 681-1; 689-1; 700-2 C. tortipalpis (5) EI; SSI 62.0–355.2 (160–4026) 605-2; 609-1; 652-1; 655-1; 664-1 C. lilliei (3) EI; SSI 151.6–467.2 (79–1119) 605-5; 661-2; 668-1 C. pseudofrigida sp. nov. (3) EI 164.9–311.7 610-1; 614-3; 621-1 C. wilsoni (1) SSI 277.4–282.9 (60–801) 660-1 C. arundorostris (2) SSI; JI a 159.2–432 a (610) 663-1; 685-1 a Novel information on the distribution patterns of the Colossendeis species examined. [In bracket previously known bathymetric range. Known bathymetric and geographic distribution data for Colossendeis species have been obtained from summarized studies: Fry and Hedgpeth 1969; Pushkin 1993; Child 1995; Cano-Sánchez and López-González 2007; Munilla and Soler-Membrives 2009]. [EWS Eastern Weddell Sea; EI: Elephant Island; SSI: South Shetland Islands; JI Joinville Island; BS Bransfield Strait; B-South Larsen B (core-station South); B-West Larsen B (core-station West); DI Dundee Island (Paulet Island)] Table 3 Main differences between Colossendeis arundorostris, C. rugosa, C. arcanus, and C. bamberi sp. nov. (value range and mean+standard deviation from measurements of the studied specimens) (in brackets holotype specimen measurements) C. rugosa C. arundorostris C. arcanus C. bamberi sp. nov. Ratio Proboscis/trunk length (1.56) 1.8 –1.84 (2.56) 2.07 + 0.43 (2.49) 1.71 –2.05 (1.9) 1.89 +0.11 Ratio 2 th /4 th palp article length (1.48) 1.44 –1.62 (1.12) 1.39 + 0.25 (1.56) 1.21 –1.55 (1.4) 1.44 +0.09 Ratio 6 th /7 h palp article length (4.25) 7 –8 (7) 7.33 + 0.58 (4.73) 4.26 –6.5 (4.26) 5.33 +0.69 Ratio length/width 7 th palp article (1) 0.9 –0.93 (1) 0.94 + 0.05 (2.67) 0.88 –1.26 (1.05) 1.09 +0.12 ratio 7 th /8 th palp article length (0.4) 0.21 –0.25 (0.2) 0.22 + 0.03 (0.33) 0.29 –0.38 (0.37) 0.35 +0.03 Ratio 9 th /8 th palp article length (1.63) 0.86 –1.08 (1.07) 1 + 0.13 (1.06) 1.07 –1.45 (1.16) 1.25 +0.1 Ratio femur/propodus length (3.63) 2.86 –3.25 (3.39) 3.17 + 0.28 (3.37) 2.64 - 3.8 (3.33) 3.18 +0.29 Ratio propodus/claw length (1.18) 1.53 –1.55 (1.71) 1.6 + 0.1 (2.05) 1.37 –1.92 (1.60) 1.63 +0.14 24 Page 6 of 16 Marine Biodiversity (2023) 53:24 and López-González 2007). This species is similar to C. speudochelata Pushkin, 1993. In fact, the holotypes of both species together with our C. australis material form a clearly defined grouping (see Fig. 1). However, characters such as >2.5 value in femur/propodus length relationship, and an inflated proboscis could be used to distinguish C. australis. Fig. 2 Colossendeis bamberi sp. nov. Holotype, male. adorsal view of body; blateral view of body; coviger; dlast strigilis article; ethird leg of right side. Scale bars: 5 mm (a,b); 4 mm (c); 0.004 mm (d); 5 mm (e) Page 7 of 16 24Marine Biodiversity (2023) 53:24 Colossendeis bamberi sp. nov. https://zoobank.org/68A83DAD-5A60-48A6-A846-D3A2D7CDB7F8 (Fig. 2) Material examined Holotype: MZB (2022-1441), one adult male, Polarstern cruiseXXIII/8,stn.677-1,SouthShetlandIslands, 62°10.70'S 60°32.79'W, 200.2–205.4 m, Bottom trawl, 02 December 2007. Paratypes: MZB (2022-1442), one adult female, Polarstern cruise XXIII/8, stn. 661-2, South Shetland Islands, 61°39.29'S 57°02.89'W, 467.2–466.0 m, Bottom trawl, 30 December 2006. MZB (2022-1443), one adult male, Polarstern cruise XXIII/8, stn. 664-1, South Shetland Islands, 61°38.86'S 57°48.04'W, 336–337.1 m, Bottom trawl, 30 December 2006. MZB (2022-1444), one adult female, Polarstern cruise XXIII/8, stn. 668-1, South Shetland Islands, 61°49.32'S 58°34.74'W, 151.6–193.0 m, Bottom trawl, 31 December 2006. MZB (2022-1445), one adult female, Polarstern cruise XXIII/8, stn. 674-1, South Shetland Islands, 61°59.10'S 59°55.57'W, 286.3–318.1 m, Bottom trawl, 01 January 2007. See sampling data of additional examined specimens of this species in Tables 1and 2and SMTable 3. Etymology This species is named in homage to the late Roger N. Bamber, for his important contribution to our current knowledge of the pycnogonid fauna. Diagnosis Proboscis length at least 1.7 times longer than trunk. Second and third lateral processes separated by at least half their own diameter. Palp 9-articled, ratio 6 th /7 th palp article length range between 4.2 and 6.5; ratio 9 th /8 th palp article less than 1.5; ratio length/width of the 7 th palp article less than 1.3. Oviger terminal article non-subchelate; terminal claw spatulate. Femur longest of the three longest leg articles; ratio propodus/claw subequal or less than 1.9. Description of the holotype (male) Size moderate for the genus, leg span 181.8 mm. Proboscis cylindrical, smooth, distal third slightly down curved, distal two-third dilated, distal third truncated distally, 1.9 times of trunk length. Trunk without segmental suture-line traces, with lateral processes well separated, at least half of processes diameter; dorsal surface and processes smooth. Abdomen erect, slightly upcurved, smooth. Ocular tubercle as a tall cone, four distinct eyes, anterior pair slightly larger than posterior. Palps 9 articled, slender, longer than proboscis, with scarcely distributed tiny setules. Fourth article has a small pore on the external distal third. Sixth article at least four times the length of seventh. Seventh article as long as wide. Eighth article about 2.7 times of the length of seventh. Ninth article slightly longer than eighth. Ovigers 10-articled and conventional, strigilis well developed, terminal article with 2 rows of elongated spines (inner row at least twice as long as previous one) and a field of shorter spines without clear pattern of rows; they are flat with pectinate borders (Fig. 2d). Terminal claw spatulate. Walking legs slender and smooth. Second coxa longer than first or third coxa. Femur longest article and both tibiae progressively decrease in length. Tarsus about 1.4 propodus in length. Claw slightly curved, about 0.6 of propodal length. Sexual pores located ventrally on second coxa of all four legs. Measurement of the holotype (mm) Length of trunk (tip of cephalic segment to tip of fourth lateral processes): 8. Width of trunk across second lateral processes: 5. Length of proboscis: 15.2. Length of abdomen: 1.9. Length of palp: 21.3; articles of palp length (1 to 9): 0.3, 7.7, 0.8, 5.5, 1.6, 2.0, 0.47, 1.27, 1.47. Length of third left leg: 88.4; length of leg 3 articles: coxa 1 1.6, coxa 2 2.0, coxa 3 1.8, femur 23.0, tibia 1 20.3, tibia 2 18.5, tarsus 10.0, propodus 6.9, claw 4.3. Length of left oviger: 32.5; length of oviger articles (1 to 10): 0.5, 0.7, 1.0, 9.7, 4.4, 10.3, 1.5, 1.5, 1.5, 1.4, ovigeral claw 0.9. Variability Table 3shows the highest and lowest values of the ratios between characters of analysed specimens. Ocular tubercle shape is similar in all specimens, it is topped by a high pointed cone but some of them (MZB 2022-1446; MZB 2022-1454) are considerably shorter. In addition, the anterior area of the cephalic segment is variable from straight to slightly inclined following the ocular tubercle profile. Distribution At present, Colossendeis bamberi sp. nov. is known from its type locality (South Shetland Islands) and Elephant Island, Joinville Island and Larsen B (core-station South) (Table 2) Remarks Colossendeis bamberi sp.nov.iscomparableto C. arcanus,C. arundorostris,andC. rugosa. The new species is grouped with the above-listed species by sharing the following set of characters: (1) ratio 6 th /7 th palp article length longer than 4.2; (2) ratio 7 th /8 th palp article length subequal or shorter than 0.4; (3) second and third lateral processes separated by more than 0.5 their own diameter; (4) oviger terminal article not subchelate; and (5) eyes developed. 24 Page 8 of 16 Marine Biodiversity (2023) 53:24 Colossendeis rugosa was included in the “C. megalonyx complex”by Fry and Hedgpeth (1969), and later only Pushkin (1993) considered it as a separate form from C. megalonyx.In our cluster analysis, C. rugosa is clearly separate from the grouping formed by C. arundorostris,C. arcanus and C. bamberi sp. nov. (see Fig. 1). Moreover, C. rugosa differs mainly from them by a higher ratio of 9 th /8 th palp article length and a lower ratio propodus/claw length (Table 3). The length ratio of the 6 th /7 th palp article is considerably higher in C. arundorostris than in C. arcanus and in C. bamberi sp. nov., while conversely the ratio 7 th /8 th palp article length is lower in C. arundorostris (Table 3). Colossendeis bamberi sp. nov. clearly differs from C. arcanus by the ratio proboscis/trunk length, the ratio length/width of the 7 th palp article, and the ratio propodus/ claw length, in all these comparisons the former species having higher values (Table 3). Colossendeis drakei Calman, 1915 Material examined See Tables 1and 2and SMTable 3. Diagnosis Proboscis length subequal or shorter than trunk. Second and third lateral processes separated by at least half their own diameter. Palp 9-articled, ratio 6 th /7 th palp article length subequal or less than 1.2. Ovigeral terminal article non-subchelate, with 4 rows of compound spines. Femur longest of the three longest leg articles, ratio propodus/claw length less than 1.3. Remarks The specimens of C. drakei examined for this study agree with the description provided by Calman (1915) and subsequent authors (Fry and Hedgpeth 1969;Pushkin1993;Child 1995; Alexeeva 2021). These authors did not indicate any special condition concerning the ovigeral claw, but Dietz et al. (2015a) pointed out that the claw appears to be bifurcated. All our specimens, however, show a spatulate ovigeral claw. Colossendeis engirmatica Turpaeva, 1974 Material examined See Tables 1and 2and SMTable 3. Diagnosis Proboscis length at least 1.5 times longer than trunk. Second and third lateral processes separated by at least half their own diameter. Palp 9-articled, 7 th palp article articulated anaxially with 8 th ; ratio 6 th /7 th palp article length subequal or greater than 6. Oviger terminal article subchelate. Second tibia shortest of the three longest leg articles. Remarks Turpaeva (1974) noted that this species closely resembles C. tortipalpis. Both species exhibit widely separated lateral processes, the 7 th palp article articulated anaxially with 8 th and the oviger terminal article subchelate. She pointed out the more separated lateral processes, the shape of ocular tubercle, the oviger structure, and the shorter claw of the legs of C. engirmatica were the differential characters. The specimens here examined agree with the description provided by Turpaeva (1974), but they show a long claw in the legs, similar to propodus in length (a similar condition to that observed in C. tortipalpis), and the ocular tubercle ranges from rounded to pointed. In our cluster analysis, C. tortipalpis and C. engirmatica are closely related (Fig. 1). They differ mainly in the relative proportion between the length of the 6 th and 7 th palp article, in C. engirmatiga group the ratio being longer than 6. Only type of material was known before, and our specimens represent the first record of this species after its original description. Colossendeis frigida Hodgson, 1907 Material examined See Tables 1and 2and SMTable 3. Diagnosis Proboscis length at least 1.6 times longer than trunk. Second and third lateral processes separated by at least half their own diameter. Palp 9-articled, ratio 6 th /7 th palp article length less than 3.4; ratio 7 th /8 th palp article greater than 0.4; ratio length/width of the 7 th palp article subequal or greater than 1.3. Oviger terminal article not subchelate. Femur longest of the three longest leg articles; ratio femur/propodus subequal or length less than 3.6. Remarks Hodgson (1907) described Colossendeis frigida and pointed out that it was very closely related to C. megalonyx, and the arguments were followed by Calman (1915) and Pushkin (1993). However, Loman (1923) suggested that both species could not be separated (favour of C. megalonyx) and this was followed by subsequent authors (Gordon 1932,1938; Fry and Hedgpeth 1969; Child 1995; Munilla and Soler-Membrives 2009; Turpaeva and Rajsky 2013;Bamberetal.2022). The specimens of C. frigida examined in this study agree with the description provided by Hodgson (1907) and Calman (1915). They can be diagnosed by the ratio of the 6 th /7 th palp article length and the ratio length/width of the 7 th palp article (see also Table 4). In our study, this species forms a clearly defined group, consisting of the holotype specimen and our 188 specimens (Fig. 1). Page 9 of 16 24Marine Biodiversity (2023) 53:24 Dietz L, Arango CP, Halanych KM et al (2015b) Regional differentiation and extensive hybridisation between mitochondrial clades of the Southern Ocean giant sea spider Colossendeis megalonyx. 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