Two new species of brittle stars (Echinodermata: Ophiuroidea), living epizoic on a stalked crinoid

176 European Journal of Taxonomy 1022: 176–201 https://doi.org/10.5852/ejt.2025.1022.3087 europeanjournaloftaxonomy.eu ISSN 2118-9773 2025 · Stöhr S. This work is licensed under a Creative Commons Attribution License (CC BY 4.0) Received: 23 April 2025 • Accepted: 12 August 2025 • Published: 10 October 2025 Topic editor: Magalie Castelin • Section editor: Didier Van den Spiegel • Desk editor: Pepe Fernández Research article urn:lsid:zoobank.org:pub:B189BB0C-3060-4DC5-8F9B-35E8088DB699 Two new species of brittle stars (Echinodermata: Ophiuroidea), living epizoic on a stalked crinoid Sabine STÖHR Swedish Museum of Natural History, Department of Zoology, Frescativägen 40, 10405 Stockholm, Sweden. Email: [email protected] Abstract. Brittle star species with epizoic life-style are found in at least a dozen families and on a wide variety of host animals (Cnidaria, Porifera, Mollusca, other Echinodermata). An overview of epizoic brittle star species is provided. This study is the first account of brittle stars living epizoic on the crinoid Neogymnocrinus richeri. Two species were described as new to science, for one of them, a new genus, Warenophis gen. nov., was erected. “Ophiomitrella” thuyi sp. nov. is tentatively placed in the genus Ophiomitrella, because the genus is polyphyletic and its type species was here found not to concur with the generic characters. All species of Ophiomitrella and Ophiosemnotes were analysed, key characters are listed, and the taxonomic status of these genera is discussed. Warenophis andersi gen. et sp. nov. possesses an unusual combination of features that doesn’t match any known genus, such as flat, serrated arm spines, large disc plates without granules or spines, arm spine articular structures with tongue-like extension, and it could not yet be placed in a family. Based on lateral arm plate characters, it has affinities with the Ophiacanthidae and Ophiotomidae. Keywords. Taxonomy, Ophiacanthidae, Ophiotomidae, Ophiomitrella. Stöhr S. 2025. Two new species of brittle stars (Echinodermata: Ophiuroidea), living epizoic on a stalked crinoid. European Journal of Taxonomy 1022: 176–201. https://doi.org/10.5852/ejt.2025.1022.3087 Introduction Ophiuroidea Gray, 1840, generally known as brittle stars, include 2136 species according to the latest census, based on published descriptions and revisionary works (Stöhr et al. 2025). Among these, a small number are known to occur epizoic or endozoic on or in other animal hosts (Table 1). Most species of ophiuroid with the ability to curl the arms (e.g., Euryalida Lamarck, 1816, Hemieuryalidae Verrill, 1899) are expected to be epizoic, but the host species are yet unknown for many of these. The ophiuroids often prefer a specific taxonomic group of hosts, e.g., Euryalida often occur on corals (many are found only on black corals), Amphiuridae Ljungman, 1867 have so far only been found associated with sea urchins, and epizoic Ophiactidae Matsumoto, 1915 seem to occur mainly on and in sponges, whereas Ophiotrichidae Ljungman, 1867 have been found on a variety of hosts (Table 1). At least one fossil ophiuroid species has been found epizoic on a crinoid (Thuy et al. 2020), indicating that these associations have a long evolutionary history. Particularly common are ophiuroid–coral relationships, and the coral most likely STÖHR S., Two new epizoic ophiuroid species 177 Table 1 (continued on next three pages). Non-exhaustive list of epizoic and endozoic species of Ophiuroidea Gray, 1840 and their host species. Compiled from the cited literature sources and museum collection specimens. Family Ophiuroid Host Source Cnidaria hosts Asteronychidae Ljungman, 1867 Asteronyx loveni Müller & Troschel, 1842 Pennatuloidea, Octocorallia Buhl-Mortensen & Buhl-Mortensen 2004 Gorgonocephalidae Ljungman, 1867 Gorgonocephalus caputmedusae (Linnaeus, 1758) Various corals, Lophelia pertusa (Linnaeus, 1758) Buhl-Mortensen & Buhl-Mortensen 2004 Gorgonocephalus eucnemis (Müller & Troschel, 1842) Gersemia v. Marenzeller, 1878, Eunephthya Verrill, 1869 Mortensen 1927; Patent 1970; Buhl-Mortensen & Buhl-Mortensen 2004 Gorgonocephalus lamarcki (Müller & Troschel, 1842) Various corals, Lophelia pertusa (Linnaeus, 1758) Buhl-Mortensen & Buhl-Mortensen 2004 Astrogordius cacaoticus (Lyman, 1874) Antipathes Pallas, 1766, Ellisella barbadensis (Duchassaing & Michelotti, 1864) Buhl-Mortensen & Buhl-Mortensen 2004 Astrothorax waitei (Benham, 1909) Corals Personal observation on museum specimen Asteroporpa annulata Örstedt & Lütken in Lütken, 1856 Various corals Buhl-Mortensen & Buhl-Mortensen 2004 Asteroporpa indicus (Baker, 1980) Coral Personal observation on museum specimen Astrothrombus rugosus H.L. Clark, 1909 Coral Personal observation on museum specimen Euryalidae Gray, 1840 Asteromorpha tenax Baker, 1980 Coral Personal observation on museum specimen Asteroschema ajax A.H. Clark, 1949 Pseudochrysogorgia bellona Pante & France, 2010 Cook et al. 2023 Asteroschema clavigerum Verrill, 1899 Paramuricea biscaya Grasshoff, 1977 Girard et al. 2016 Asteroschema tenue Lyman, 1875 Corals Buhl-Mortensen & Buhl-Mortensen 2004 Asteroschema tubiferum Matsumoto, 1911 Coral Personal observation on museum specimen Asteroschema tumidum Lyman, 1879 Coral Personal observation on museum specimen Astroceras elegans (Bell, 1917) Coral Personal observation on museum specimen European Journal of Taxonomy 1022: 176–201 (2025) 178 Table 1 (continued). Family Ophiuroid Host Source Euryalidae Gray, 1840 Ophiocreas oedipus Lyman, 1879 Metallogorgia melanotrichos (Wright & Studer, 1899) Mosher & Watling 2009 Ophiocreas sibogae Koehler, 1904 Coral Personal observation on museum specimen Astrobrachion constrictum (Farquhar, 1900) Antipathella fiordensis (Grange, 1990) Grange 1991 Ophiomusaidae O’Hara, Stöhr, Hugall, Thuy & Martynov, 2018 Ophiomusa lymani (Wyville Thomson, 1873) Acanella arbuscula (Johnson, 1862), gorgonians Buhl-Mortensen & Buhl-Mortensen 2004 Ophiacanthidae Ljungman, 1867 Ophiocanops felli McKnight, 2003 Antipathes Pallas, 1766 McKnight 2003 Ophiocanops multispina Stöhr, Conand & Boissin, 2008 Antipathes Pallas, 1766 Stöhr et al. 2008 Ophioplinthaca citata Koehler, 1904 Primnoidae O’Hara & Stöhr 2006 Ophiomoeris obstricta (Lyman, 1878) Soft corals, sponges O’Hara & Stöhr 2006 Ophiosemnotes clavigera (Ljungman, 1865) Lophelia pertusa (Linnaeus, 1758), Paramuricea placomus (Linnaeus, 1758) Buhl-Mortensen & Buhl-Mortensen 2004 Ophiacantha abyssicola G.O. Sars, 1872 Various corals, Lophelia pertusa (Linnaeus, 1758) Buhl-Mortensen & Buhl-Mortensen 2004 Ophiosabine anomala (G.O. Sars, 1872) Various corals, Lophelia pertusa (Linnaeus, 1758) Buhl-Mortensen & Buhl-Mortensen 2004 Ophiacantha bidentata (Bruzelius, 1805) Lophelia pertusa (Linnaeus, 1758) Allen Brooks et al. 2007 Ophiacantha setosa (Bruzelius, 1805) Corals Tortonese 1965 Ophiomitrella mensa O’Hara & Stöhr, 2006 Cnidaria O’Hara & Stöhr 2006 Ophiotomidae Paterson, 1985 Ophiotreta valenciennesi (Lyman, 1879) Lophelia pertusa (Linnaeus, 1758) Stöhr & Segonzac 2005 Hemieuryalidae Verrill, 1899 Astrogymnotes irimurai Baker, Clark & McKnight, 2001 Antipathes Pallas, 1766 Baker et al. 2001; Buhl-Mortensen & Buhl-Mortensen 2004 Hemieuryale pustulata v. Martens, 1867 Nicella guadalupensis (Duchassaing & Michelotti, 1860) Gondim et al. 2015 Sigsbeia murrhina Lyman, 1878 Stylaster filogranus Pourtalés, 1871 Lyman 1878 STÖHR S., Two new epizoic ophiuroid species 179 Family Ophiuroid Host Source Sigsbeia laevis Ziesenhenne, 1940 “red coral” Ziesenhenne 1940 Ophiotrichidae Ljungman, 1867 Macrophiothrix melanosticta (Grube, 1868) Pennatuloidea Hoggett 1990 Ophiothela danae Verrill, 1869 gorgonians Fatemi & Stöhr 2019 Ophiothela venusta (de Loriol, 1900) Suberogorgia suberosa (Pallas, 1766) Fatemi & Stöhr 2019 Ophiothrix savignyi (Müller & Troschel, 1842) Suberogorgia suberosa (Pallas, 1766) Fatemi & Stöhr 2019 Ophiocnemis marmorata (Lamark, 1816) rhizostome jellyfish Fujita & Namikawa 2006 Echinodermata hosts Gorgonocephalidae Ljungman, 1867 Astrothorax waitei (Benham, 1909) Crinoidea T. O’Hara, observation on museum specimen Amphiuridae Ljungman, 1867 Amphipholis linopneusti Stöhr, 2001 Linopneustes murrayi (A. Agassiz, 1879) Stöhr 2001 Amphipholis conolampadis Kroh & Thuy, 2013 Conolampas diomedeae Mortensen, 1948 Kroh & Thuy 2013 Ophiodaphne formata (Koehler, 1905) Astriclypeus manni Verrill, 1867 Tominaga et al. 2004 Ophiodaphne spinosa Tominaga, Hirose, Igarashi, Kiyomoto & Komatsu, 2017 Clypeaster japonicus Döderlein, 1885 Tominaga et al. 2017 Nannophiura lagani Mortensen, 1933 Laganum depressum L. Agassiz, 1841 Mortensen 1933 Ophiotrichidae Ljungman, 1867 Ophiomaza cacaotica Lyman, 1871 Crinoidea, Comatulida Potts 1915; Mekhova & Britayev 2015 Gymnolophus obscura Ljungman, 1867 Crinoidea Potts 1915 Ophiolophus novarae Marktanner-Turneretscher, 1887 Comanthus bennetti (J. Müller, 1841) Guille et al. 1986 Ophiophthirius actinometrae Döderlein, 1898 Actinometra solaris (Lamarck, 1816) Döderlein 1898 Macrophiothrix melanosticta (Grube, 1868) Crinoidea Hoggett 1990 Ophiacanthidae Ljungman, 1867 Ophiacantha pentacrinus Lütken, 1869 Endoxocrinus (Endoxocrinus) parrae parrae (Gervais in Guérin, 1835) Lütken 1869 Ophiolebes comatulina McKnight, 2003 Comatulida McKnight 2003 Ophiolebes paulensis O’Hara & Thuy, 2022 Crinoidea O’Hara & Thuy 2022 Table 1 (continued). European Journal of Taxonomy 1022: 176–201 (2025) 180 functions as a perch for the (usually particle feeding) ophiuroid to reach higher water layers above the sea floor. In most cases, the ophiuroid-coral relationship is considered facultative, but a few species appear not to be able to live without their host, e.g., Asteronyx loveni Müller & Troschel, 1842 (Buhl-Mortensen & Buhl-Mortensen 2004). Among the more unusual relationships are ophiuroids riding on pelagic jellyfish (Fujita & Namikawa 2006), and the observation of Ophiomusa lymani (Wyville Thomson, 1873) on gorgonian corals (Buhl-Mortensen & Buhl-Mortensen 2004) is unexpected in a species with rather rigid arms that usually lives on the open bottom of the deep-sea plains (Gage & Tyler 1991). Several species of ophiuroid are known to live on crinoids (Table 1), and this study reports two additional species that were found on the stalked cyrtocrinid Neogymnocrinus richeri (Bourseau, AmézianeCominardi & Roux, 1987) in the Tonga Islands. As far as known, these are the first records of epizoic Family Ophiuroid Host Source Ophiacanthidae Ljungman, 1867 Ophiomitrella floorae Thuy, Numberger-Thuy & Jagt, 2020 (fossil) Crinoidea Thuy et al. 2020 “Ophiomitrella” thuyi sp. nov. Neogymnocrinus richeri (Bourseau, AmézianeCominardi & Roux, 1987) Present study Ophiacanthida incertae sedis Warenophis andersi gen. et sp. nov. Neogymnocrinus richeri (Bourseau, AmézianeCominardi & Roux, 1987) Present study Porifera hosts Ophiactidae Matsumoto, 1915 Ophiactis savignyi (Müller & Troschel, 1842) Porifera Hendler et al. 1995; Fatemi & Stöhr 2019 Ophiactis algicola H.L. Clark, 1933 Porifera, Bryozoa Hendler et al. 1995 Ophiactis quinqueradia Ljungman, 1872 Porifera Hendler et al. 1995 Ophiactis modesta Brock, 1888 Porifera Peyghan et al. 2018 Ophiotrichidae Ljungman, 1867 Ophiothrix angulata (Say, 1825) Porifera Hendler et al. 1995 Ophiothrix suensonii Lütken, 1856 Porifera Hendler et al. 1995 Ophiothrix lineata Lyman, 1860 Porifera Hendler et al. 1995 Ophiothrix oerstedii Lütken, 1856 Porifera Hendler et al. 1995 Mollusca hosts Amphilepidida O’Hara, Hugall, Thuy, Stöhr & Martynov, 2017 Ophienigma spinilimbatum Stöhr & Segonzac, 2005 Bathymodiolus Kenk & B.R. Wilson, 1985 Stöhr & Segonzac 2005 Ophiuridae Müller & Troschel, 1840 Ophioctenella acies Tyler, Paterson, Sibuet, Guille, Murton & Segonzac, 1995 Bathymodiolus Kenk & B.R. Wilson, 1985 Tyler et al. 1995 Table 1 (continued). STÖHR S., Two new epizoic ophiuroid species 181 brittle stars from this species of crinoid. Both species of ophiuroid are new to science, and the aim of this study was to describe them and to understand their systematic relationships. One of these species has a highly unusual morphology that does not concur with any known genus, and it has uncertain affinities to higher taxa. The other species has affinities with the genus Ophiomitrella Verrill, 1899, a polyphyletic complex of morphologically highly similar species, from which one molecular clade was recently separated and placed in the genus Ophiosemnotes Matsumoto, 1917 (O’Hara & Thuy 2022). The discovery of the new species prompted an investigation into the taxonomic status of Ophiomitrella, attempting to find morphological characters that may be useful to delimit monophyletic clades, ideally in agreement with the molecular clades found by Christodoulou et al. (2019). Material and methods The ophiuroids were discovered on a specimen of N. richeri that was collected during the cruise Bordau 2 to the Tonga Islands in 31 Mar.–22 Jun. 2000 (Richer de Forges 2000). They were stored in 80% ethanol. The ophiuroids were clinging to the oral side of the crinoid, with their arms tightly wrapped around the crinoid arms (observation by the author). During removal of the ophiuroids, their arms broke, unfortunately. One specimen each was subjected to diluted household bleach, to gently remove the outer skin. They were then air-dried, mounted on aluminium stubs with spray glue, and coated with gold for examination in a scanning electron microscope Hitachi FE-S4300. After scanning the dorsal side, they were removed from the stubs by dissolving the glue in butyl acetate, turned over and re-attached with fresh glue, to scan also the ventral side of the animals. An arm piece of the unknown genus was dissolved in concentrated bleach to dissociate the ossicles. These were then glued to SEM stubs and examined in the instrument. To identify the specimens of “Ophiomitrella”, all species currently assigned to Ophiomitrella and Ophiosemnotes were analysed from their original descriptions and actual type specimens or digital photos of the type specimens, as available, and four key characters were compared (Table 2). Since the specimens did not match any of the known species, they are described as new. The second species did not match any known genus or species and both a new genus and a new species are described below. To place it in the ophiuroid classification, its lateral arm plates were compared with species across the whole Ophiuroidea. After its greatest similarities were found to be with Ophiacanthida O’Hara et al., 2017, it was compared with several genera in the families Ophiacanthidae Ljungman, 1867 and Ophiotomidae Paterson, 1985. The terminology for morphological characters follows common practice in the field (Stöhr et al. 2012). Terms for oral structures follow Hendler (2018) as far as they could be identified. The more generic term ‘lateral oral papillae’ was used for papillae that cannot be identified in the absence of ontogenetic series. To understand the phylogenetic relationships of the new genus, a Bayesian phylogenetic analysis was performed using the software package MrBayes (Huelsenbeck & Ronquist 2001) with the same parameters and family level morphological characters as in Stöhr (2024), but with a partly different set of species. Particularly, two species of Ophiolimna Verrill, 1899, and Ophiocopa spatula Lyman, 1883, were added to the data matrix, since their spine articular structures on the lateral arm plates resemble the new genus. Also, these represent two different families and complete sets of characters were available. The dataset contained 153 characters and 71 species (Supp. file 1). To compare tree structures, the analysis was run without the new genus. In addition, an analysis with only the 46 characters from lateral arm plates was run, since these have been shown to be taxonomically highly informative (Thuy & Stöhr 2011), and for the new genus and species not all other structures were available. Only variable characters were sampled, and the coding parameter was set to variable in the Bayesian analysis. Character states were assumed to have equal frequency, and prior probabilities were equal for all trees. As outgroup, Aganaster gregarius (Meek & Worthen, 1869) was used. Evolutionary rates were assumed to vary between sites according to a discrete gamma distribution. Branch lengths were unconstrained. The average standard European Journal of Taxonomy 1022: 176–201 (2025) 182 deviation of split frequencies stabilized at about 0.006–0.01 after nine million generations, sampled every 1000 generations. The first 25% of the trees were discarded as burnin. The resulting consensus trees were examined with the software FigTree ver. 1.4.4 by Rambaut (https://tree.bio.ed.ac.uk/software/figtree/). Abbreviations ars = articular structure AS = adoral shield ASP = arm spine CP = compartment plate DAP = dorsal arm plate dd = disc diameter dist = distal dl = dorsal lobe dors = dorsal IR = interradial plate LAP = lateral arm plate LOPa = lateral oral papillae OS = ral shield prox = proximal RS = radial shield SEM = scanning electron microscope sp = spur TP = tooth papillae TS = tentacle scale VAP = ventral arm plate vars = vertebral articular structure vent = ventral Institutional acronyms MNHN = Muséum national d’Histoire naturelle, Paris SMNH = Swedish Museum of Natural History, Invertebrate collection, Stockholm Results Taxonomy Class Ophiuroidea Gray, 1840 Superorder Ophintegrida O’Hara, Hugall, Thuy, Stöhr & Martynov, 2017 Order Ophiacanthida O’Hara, Hugall, Thuy, Stöhr & Martynov, 2017 Family Ophiacanthidae Ljungman, 1867 Genus Ophiomitrella Verrill, 1899 Fig. 1; Table 2 Type species Ophiacantha laevipellis Lyman, 1883. Material examined ANTARCTICA – Maria Island • 1 spec., syntype of Ophioripa conferta; depth 1300 fathoms (2379 m); 13 Dec. 1912; Australasian Antarctic Expedition; MNHN, MNHN-IE-2013-10230 (formerly Ec Os 20388). STÖHR S., Two new epizoic ophiuroid species 183 CHILE – Gulf of Ancud • 3 specs, syntypes of Ophiomitrella chilensis; Paso Tenaún, S of Punta Tenaún; 42°20′50″ S, 73°22′00″ W; depth 70 m; 24 Jan. 1949; Lund University Chile Expedition stn M42; triangular dredge; hard bottom; SMNH, SMNH-Type-2321. INDONESIA – Kei Island • 1 spec., syntype of Ophiacantha tenuis; 5°48.2′ S, 132°13′ W; depth 304 m; 1899–1900; Siboga Expedition stn 253; MNHN Ec Os 2040. NORWAY • 3 specs, syntypes of Ophiactis clavigera; depth 364–546 m; 22 Oct. 1864; Uggla Expedition; on Gorgonia; SMNH, SMNH-Type-3724. SOUTH ATLANTIC OCEAN – Gough Island • 1 spec., syntype of Ophiomitrella ingrata; depth 100 fathoms (183 m); 23 Apr. 1904; Scotia Expedition; MNHN, MNHN-IE-2013-10308 (formerly Ec Os 20364). WEST INDIES – off St. Vincent • 1 spec., paratype of Ophiacantha laevipellis; depth 88 fathoms (160 m); 21 Feb 1879; Blake stn 232; MNHN, MNHN-IE-2013-10160 (formerly Ec Os 20398). Remarks When Verrill (1899a) erected Ophiomitrella, he described it in a confusing dichotomous list, from which it is difficult to extract the characters that delimit this genus. Under section “A”, he sorted species in which the adoral shields are restricted to the proximal part of the oral shield, but under “A.A.” they extend around the oral shield. Ophiomitrella is found under “B.B.”, which doesn’t mention adoral shields, but has uncovered radial shields, whereas “B.” is meant for species with covered radial shields. Finally, under “n.n.”, Ophiomitrella has separated dorsal arm plates and thorny, slender arm spines that meet dorsally. The only species assigned to Ophiomitrella was O. laevipellis, making it the type species of the genus by monotypy. According to the redescription (Verrill 1899b), Ophiomitrella should have small, widely separated radial shields, not bearing granules or spines, adoral shields limited to the proximal part of the oral shield, disc with scattered granules or stumps. In the same work (Verrill 1899b), O. laevipellis is described as having long, narrow, covered radial shields, with only their distal part exposed, which was here confirmed by examination of publicly available photos of the holotype (MCZ:IZ:OPH-1957) and photos of a paratype taken by the author (Fig. 1I–J). Verrill subdivided Ophiomitrella, based on differences in arm spines, and placed O. laevipellis in one subgroup, whereas Ophiomitrella cordifera (Koehler, 1896) and Ophiomitrella globulifera (Koehler, 1896) formed the other subgroup. The latter two species match the description of the genus Ophiomitrella, which is however still a polyphyletic genus (O’Hara et al. 2018), despite the recent transfer of a group of species to the morphologically highly similar genus Ophiosemnotes (O’Hara & Thuy 2022). The necessary revision of these genera is far beyond the scope of this study, and as O’Hara & Thuy (2022) found, morphological characters that support the molecular clades have not been identified yet. In Table 2, the species were grouped by the nature of their disc spines (granules are considered homologous to spines). The majority of the species have more or less spherical (granule-like) disc spines, and the removal of Ophiosemnotes brevispina (H.L. Clark, 1911), that lacks disc spines, and Ophiosemnotes diaphora (H.L. Clark, 1911), that has granules, from the Ophiosemnotes group concurs with the latest published molecular phylogeny (Christodoulou et al. 2019). Thus, a revision of Ophiosemnotes appears necessary. However, on that tree, these two species are also in a separate clade from the remaining Ophiomitrella, and other members of this group are found in several clades on the molecular phylogeny (Christodoulou et al. 2019), which suggests that the granular disc spine group may be polyphyletic. Several of the species with stellate disc spines form a clade on the molecular tree, but the clade includes also Ophiomitrella barbara Koehler, 1904, which was here grouped as having elongated European Journal of Taxonomy 1022: 176–201 (2025) 184 Fig. 1. Type specimens of some species currently placed in the genera Ophiomitrella Verrill, 1899 and Ophiosemnotes Matsumoto, 1917. A–B. Ophiacantha tenuis Koehler, 1904, syntype (MNHN Ec Os 20408). A. Dorsal disc. B. Mouth. C–D. Ophiomitrella ingrata Koehler, 1908, syntype (MNHNIE-2013-10308). C. Dorsal disc. D. Mouth. E–F. Ophiomitrella chilensis Mortensen, 1952, syntype (SMNH-Type-2321). E. Dorsal disc. F. Mouth. G–H. Ophioripa conferta Koehler, 1922, syntype (MNHN-IE-2013-10230). G. Dorsal disc. H. Mouth. I–J. Ophiacantha laevipellis Lyman, 1883, paratype (MNHN-IE-2013-10160). I. Dorsal disc. J. Mouth. Arrows point to radial shields, arrowheads mark adoral shields. Scale bars = 1 mm. STÖHR S., Two new epizoic ophiuroid species 191 Description Holotype Dorsal Disc. 4.8 mm dd, pentamerous. Round, domed disc, centre with irregular scales of variable size, no granules or spines. Radial shields scalene triangular, about as long as ⅓ of dd, completely contiguous. Primary rosette not distinguishable. Large rectangular interradial scale separates pairs of radial shields. V entral Disc . Covered by scales smaller than on dorsal disc. Oral shield rhombic, 1.5 times as wide as long, distal edge convex, madreporite larger, no hydropore visible. Adoral shields crescent-shaped, proximal edge slightly concave, restricted to proximal edges of oral shield. Short jaws with two fingerlike tooth papillae, teeth wide, rounded. Three minute, round granule-like lateral oral papillae. Large superficial second tentacle pore outside mouth slit, with oval, scale-like adoral shield spine at edge of adoral shield. arms. Dorsal arm plates fan-shaped, as long as wide, contiguous. Lateral arm plates forming part of dorsal arm. Up to four arm spines, two dorsal spines largest, flat, triangular, proximal edge convex, distal edge straight, perpendicular to arm, imbricated, roof-like horizontal. Spines smaller on distal arm, but same flat shape throughout arm. Two ventral spines shorter, narrower, flattened. All arm spines with serrated edges. Ventral arm plates widely axe-shaped, twice as wide as long, lateral edges deeply excavated, distal edge straight, proximal edge wide flat angle, barely contiguous. Single round tentacle scale, not completely closing pore. colouration. Dark green, similar to host N. richeri, faded in alcohol. Ossicles lateral arm plates. Outer side with three to four spine articular structures on elevated part, shaped as two lobes, almost vertical in position, dorsal lobe tongue-shaped widened, ventral lobe short, muscle opening larger than nerve opening. Proximal outer edge of LAP with median process (spur). Stereom finely porous, along proximal edge a finer meshed band. Vertebral articular structures on inner side as angled flat ridge with finer pores than surrounding stereom, and round low knob on ventro-proximal part. Large pores distal to ridge, flat spur median on distal part. arm spines. Articular structures as oval, flat, smooth knob with median slit and deep groove dorsodistal to knob. On largest spine, articular structures offset to distal part of lateral edge. Vertebrae. Zygospondylous articulation with zygosphene as long as zygocondyles, extending beyond lower ends of zygocondyles. No dorsal keel-like structure. Paratypes Specimen A: 4.1 mm dd, disc damaged, but plates and scales similar to holotype. Two arms completely broken off, three at distance from disc. Arms and ventral disc like holotype. Tentacle scale smaller than in holotype. Arm pieces present in sample. Specimen B: juvenile of 2.2 mm dd, dorsal disc with pentagonal central primary plate, slightly smaller, rounded square radial primary plates, small pentagonal proximal interradial plate, larger rectangular distal interradial plate. Radial shields scalene triangular, contiguous. Oral papillae as in other paratype and holotype. Large tentacle pores with single minute scale. Small arm pieces in sample, all but one arm broken off close to disc. European Journal of Taxonomy 1022: 176–201 (2025) 192 Fig. 3. Warenophis andersi sp. nov. A–E. Holotype (MNHN-IE-2023-164), SEM images. A. Dorsal overview. B. Dorsal disc and arms. C. Proximal arm, laterally. D. Distal arm, dorsally. E. Mouth. F. Ventral arm. G–J. Paratypes (SMNH-Type-10005), digital photos. G, I. Dorsal aspects. H, J. Ventral aspects. Abbreviations: ars = articular structure; AS = adoral shield; ASP = arm spine; DAP = dorsal arm plate; IR = interradial plate; LAP = lateral arm plate; LOPa = lateral oral papillae; OS = oral shield; RS = radial shield; TP = tooth papillae; TS = tentacle scale; VAP = ventral arm plate. Scale bars: A–B, F–J = 1 mm; C–E = 0.5 mm. STÖHR S., Two new epizoic ophiuroid species 193 Fig. 4. Arm ossicles, SEM images. A–D, M–N. Warenophis andersi gen. et sp. nov. (SMNHType-10005). A–C. LAP. A. External aspect. B. External aspect, slightly angled. C. Internal aspect. D. Vertebra, distal face. E–F, P. Ophiacantha bidentata (Bruzelius, 1805) (SMNH-111042), LAP. E. External aspect. F. Internal aspect. G–H. Ophiolimna antarctica (Lyman, 1879) (SMNH-127060), LAP. G. External aspect. H. Internal aspect. I–J. Ophiomitra leucorhabdota (H.L. Clark, 1911) (SMNH90622), LAP. I. External aspect. J. Internal aspect. K–L, O. Ophiocopa spatula Lyman, 1883 (SMNH131566), LAP. K. External aspect. L. Internal aspect. M. Dorsal spine. N. Ventral spine. O. Arm spine. P. Arm spine. Abbreviations: ars = articular structure; dist = distal; dl = dorsal lobe; dors = dorsal; LAP = lateral arm plates; prox = proximal; sp = spur; vars = vertebral articular structure; vent = ventral. Scale bars: A–D, M = 250 µm; E–J = 1 mm; K–L = 0.5 mm; N–P= 100 µm. European Journal of Taxonomy 1022: 176–201 (2025) 194 Remarks The taxonomic affinities of Warenophis andersi gen. et sp. nov. can be narrowed down to two families, Ophiacanthidae and Ophiotomidae. These are closely related and share numerous characters. All known ophiotomid genera have disc spines or granules, but the ophiacanthid genus Ophiohamus O’Hara & Stöhr, 2006 completely lacks disc armament, thus resembling the new species (O’Hara & Stöhr 2006). The flat, serrated arm spines of W. andersi are similar to those of Ophiotomidae, particularly Ophiocopa Lyman, 1883 and Ophiopristis Verrill, 1899. The analysis of the lateral arm plates showed that both families have a tendency to a tongue-like extension of the dorsal lobe of the spine articular structures (Fig. 4E, G, I, K), particularly obvious in Ophiolimna (Fig. 4G). The sigmoidal fold that is typical for the order Ophiacanthida is weakly expressed in the new species. The LAP of W. andersi has a proximal spur, which is more similar to Ophiotomidae than to Ophiacanthidae. Ophiotomidae LAPs have less conspicuous striations than those of Ophiacanthidae or they are limited to a small area, the new species lacks striations. The wavy border along the row of spine articulations on the LAPs is missing in W. andersi, but a slight elevation is present. The vertebral articular structure on the inner surface of the LAPs has the shape of a digit one (Numberger-Thuy & Thuy 2020) or an upside down check mark in Ophiacanthidae (Fig. 4F, H), but has an elongated dorsal extension in some Ophiotomidae, e.g., in Ophiomitra leucorhabdota (Fig. 4I), and in the new species it is a diagonal ridge, similar to Ophiocopa spatula (Fig. 4C, L). This ridge could be homologous to the long part of the digit one or a shortened version of the ophiotomid ridge, with the short downwards pointing proximal part missing. The articular structures on the arm spines are similar between the new species and Ophiacantha and Ophiocopa (Fig. 4M–P), perhaps slightly more similar to Ophiocopa. The evidence gathered from the new species is inconclusive, but Ophiacanthida is the most likely order. Ophiacanthidae is polyphyletic, and Ophiotomidae may need to be revised due to its type species appearing to be an ophiacanthid (O’Hara, unpubl. data). Family placement is proposed as incertae sedis until more data are available and the taxonomic issues with these families have been resolved. The Bayesian phylogenetic inference places W. andersi gen. et sp. nov. on the same major branch as Ophiacanthida, but not close to Ophiacanthina O’Hara, Hugall, Thuy, Stöhr & Martynov, 2017 (Fig. 5). The tree is more comb-shaped within the clade that holds the Ophiacanthina and its allies, compared to the tree inferred from the dataset excluding W. andersi (Fig. 6). The addition of the new species to the dataset has caused Ophioleucida O’Hara, Hugall, Thuy, Stöhr & Martynov, 2017 to form a sister group to the rest of the clade, albeit still paraphyletic for Ophiernidae O’Hara, Stöhr, Hugall, Thuy & Martynov, 2018, and the Ophiodermatina Ljungman, 1867 are left paraphyletic for Ophiomyxidae Ljungman, 1867. Ophiocopa spatula is morphologically similar to Ophiocamax vitrea Lyman, 1878 and thus clusters with Ophiocamacidae O’Hara, Stöhr, Hugall, Thuy & Martynov, 2018, leaving the Ophiotomidae paraphyletic. The addition of more species (Ophiactis profundi Lütken & Mortensen, 1899, two Ophiolimna, and O. spatula) has caused small changes in the tree structure and node support values, compared to previously published versions of the dataset (Thuy & Stöhr 2016; Stöhr 2024), but the division into major clades is the same. The dataset for W. andersi is incomplete and lacks all inner disc skeletal characters, because a lack of material did not allow the sacrifice of a specimen for dissociation of the disc ossicles. The homologies of the oral papillae could not be assessed, since the necessary ontogenetic series is not available, but the proximal papillae below the teeth were interpreted as tooth papillae and it is assumed that there should be infradental papillae and an adoral shield spine at the second tentacle scale. Incomplete data can have a negative effect on the analysis, as was also observed in the test run with only LAP characters (Supp. file 2), which resulted in a comb-shaped tree structure with broken up Amphilepidida O’Hara, Hugall, Thuy, Stöhr & Martynov, 2017. Only the Ophiacanthida still formed a clade similar to the complete analysis, and W. andersi is confirmed in the clade that contains the Ophiacanthida, but not within that order. Molecular data may also be needed, but the type material is suspected to have been preserved in denatured ethanol originally and none of the unique specimens could be sacrificed with such uncertain expected outcome. STÖHR S., Two new epizoic ophiuroid species 195 Discussion Reconciling the phylogeny of the Ophiuroidea, mostly inferred from molecular data, with its classification into formal taxon categories such as genera and families, is difficult and still highly incomplete. Placing new species in badly delimited higher taxa would add unnecessary confusion. Warenophis gen. nov. shares characters with two polyphyletic families (Ophiacanthidae, Ophiotomidae) and molecular data may be needed to resolve its phylogenetic position. “Ophiomitrella” thuyi sp. nov. could not be placed Fig. 5. Bayesian phylogenetic tree of Ophiuroidea Gray, 1840, based on morphological family level characters, showing the position of Warenophis andersi gen. et sp. nov. (red). Fossil species are marked by a cross. Node support values are posterior probabilities. European Journal of Taxonomy 1022: 176–201 (2025) 196 in a genus, because its affinities are with a genus that is both polyphyletic and invalid, since the generic type species does not show the characters that delimit Ophiomitrella, and it cannot at present be decided to which genus the type species belongs, due to the polyphyly of Ophiomitrella and Ophiotomidae. More specimens of both new species are needed to allow dissection for internal structures of the disc (e.g., genital plates) and molecular analysis. It would also be interesting to study how many specimens of N. richeri carry these brittle stars by examining a larger sample of crinoids. Fig. 6. Bayesian phylogenetic tree of Ophiuroidea Gray, 1840, based on morphological family level characters, Warenophis andersi gen. et sp. nov. omitted. Fossil species are marked by a cross. Node support values are posterior probabilities. STÖHR S., Two new epizoic ophiuroid species 197 The possible benefits of an epizoic life-style to the ophiuroid are badly known for most species. Living on a sessile stalked crinoid limits movement for the ophiuroids, but it is currently unknown, if they can leave their host and move to a new host or live independently. Both brittle star species had the same colour as the crinoid and were thus well camouflaged, which might suggest that they are adapted to this particular host. All epizoic brittle star species found on crinoids belong to the families Ophiacanthidae or Ophiotrichidae (Table 1). Both families are generally known to be suspension feeders (Metaxas & Giffin 2004; Calero et al. 2018), and clinging to the crinoid arms, they may benefit from the particle flow down the arms generated by the feeding crinoid. In this context, it is surprising that two different species of ophiuroid co-exist on the same host specimen, and with several individuals each. Their reproduction mode is unknown, but there was no evidence of brooding, and the presence of different size individuals, including a juvenile, suggests several recruitment events. It would be helpful to know the occurrence frequency of the ophiuroids on the crinoids. More research is needed to understand the function or evolutionary advantage of the flat, serrated arm spines of W. andersi gen. et sp. nov., which would promote secure attachment to the crinoid, provide armour-like protection or even aid in filterfeeding. Acknowledgements I’m very grateful to Anders Warén for collecting the specimens and bringing them to my attention. The Bordau 2 research cruise took place on board RV Alis, May 30–June 22, 2000, led by principal investigator Bertrand Richer de Forges, in the Tonga archipelago as part of the Tropical Deep-Sea Benthos program. It operated under a permit delivered by the Kingdom of Tonga. Many thanks also to Marc Eléaume for supplying catalogue numbers for the holotypes. 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