Ophiosabine, O’Hara & Thuy, 2022

O’Hara, Timothy D. & Thuy, Ben, 2022, Biogeography and taxonomy of Ophiuroidea (Echinodermata) from the Îles Saint- Paul and Amsterdam in the southern Indian Ocean, Zootaxa 5124 (1), pp. 1-49 : 17-18

Genus Ophiosabine gen. nov.

http://zoobank.org/ urn:lsid:zoobank.org:act:19CBDBB0-7DF5-46C7-9C62-592BD6EC0A80

Diagnosis. Disc covered in thin scales and armoured with stout thorny spines, smooth spines or granules; radial shields mostly obscured, only evident by a shallow furrow and small exposed distal section on the disc; oral shields 1–3 times longer than wide, pentagonal to square, with an obtuse proximal angle or straight proximal margin and rounded to square distal margin; adoral shields small, usually situated proximal to the oral shields; 3–5 spiniform oral papillae, the outer one usually widened, suboral papillae can be present around the second oral tentacle pore; DAPs triangular to fan-shaped, separate, sometimes edged with small thorns; VAPs with an obtuse angle proximally, and an uplifted rounded distal edge, can be glassy and striated; 6–10 long hollow cylindrical arm spines, rounded at tip, finely denticulate; tentacle pores small, one large oval to pointed tentacle scale on most pores, sometimes two on first arm segment.

Included species. Ophiacantha rosea Lyman, 1878b (type species);

Ophiacantha anomala Sars, 1872 ; Ophiacantha aristata Koehler, 1896b ; Ophiacantha cuspidata Lyman, 1878b ; Ophiacantha densispina Mortensen, 1936 ; Ophiacantha nodosa Lyman, 1878b ; Ophiacantha notata Koehler, 1906 ; Ophiacantha parcita Koehler, 1906 ; Ophiacantha pentactis Mortensen, 1936 ; Ophiacantha vivipara Ljungman, 1871 ; Ophiacantha wolfarntzi Martín-Ledo et al., 2013 .

Remarks. The molecular phylogenies presented in O’Hara et al. (2017) and Christodoulou et al. (2019) show that the genus Ophiacantha Müller & Troschel, 1842 , is polyphyletic, with some species even occurring in the Ophiotomidae (see O. spectabilis below). Amongst the many nominal Ophiacantha species that are not closely related to the type species O. bidentata ( Bruzelius 1805) , there is a monophyletic clade with a coherent morphology that contains the species O. rosea and O. vivipara that is here named as a new genus Ophiosabine . The most prominent feature is the unusual oral shield that usually is longer than wide and can be almost rectangular in some species (e.g., O. rosea ) and the small interradially-contiguous adoral shields that are placed proximal to the oral shields.

There is DNA evidence that, as well as O. rosea and O. vivipara , this genus includes the Southern Ocean O. pentactis , O. densispina and O. wolfarntzi , as well as the Atlantic species O. anomala , O. cuspidata , O. aristata ( Christodoulou et al. 2019; Martín-Ledo et al. 2013; O’Hara et al. 2013). In addition, the Atlantic species O. nodosa , O. notata and O. parcita share many morphological features of the group. Several taxonomists have noted the similarity of the six-armed O. nodosa and O. anomala ( Mortensen 1933c; Paterson 1985). However, Paterson (1985) found morphological characters that distinguished the two species and the two species differ in depth distribution, with the holotype and only known specimen of O. nodosa collected from much lower depths (2789 m) than is characteristic for O. anomala (141–1200 m). As well as the typical oral shield, O. notata and O. parcita share the glassy striated nature of the VAPs that occur in O. wolfarntzi .

Several other little-known species are also similar but have been described or figured with certain morphological features that make their assignment to Ophiosabine uncertain. The Atlantic species O. lineata Koehler, 1896a and O. metallacta H.L. Clark, 1915 have disc spines in the form of short cylindrical stumps with a rim of thorns. Ophiomitrella porrecta Koehler, 1914 from the Straits of Magellan (636 m) has a very elongated jaw, Ophiacantha atopostoma H.L. Clark, 1911 from the Bering Sea (629–681 m) has round exposed patches on the radial shields, and O. acanthinotata H.L. Clark, 1911 from Japan (309–331 m) has oral shields that “tend to become triangular”. All these species require further critical examination.

There are also numerous cryptic species in this group which complicate the nomenclature. Ophiosabine vivpara consists of three clades in the Southern Ocean ( Brogger & O’Hara 2015; O’Hara et al. 2013). Ophiosabine rosea consists of numerous clades around Australia / New Zealand and New Caledonia ( Christodoulou et al. 2019; O’Hara et al. 2013), which may not be the same species as the type collected from off Chile. COI sequences of O. densispina from South Georgia ( Martín-Ledo et al. 2013) are distinct from those around southern Australia ( O’Hara et al. 2013). There is a second unnamed species at South Georgia closely related to O. wolfarntzi ( Martin-Ledo, 2013) .

The micromorphology of ophiuroid lateral arm plates has been shown to yield a wealth of characters potentially relevant for taxon diagnoses and phylogenetic analyses ( Martynov 2010; Thuy & Stöhr 2011, 2016). A recent study suggested that lateral arm plate morphologies among species of the Ophiacanthidae are consistent with clades resolved by molecular evidence ( Numberger-Thuy & Thuy 2020; O’Hara et al. 2017). Although the number of species analysed by Numberger-Thuy and Thuy (2020) only reflects a small part of the ophiacanthid spectrum, the study suggests that the lateral arm plates of Ophiosabine rosea have a uniquely shaped vertebral articular structure on their inner side. In order to corroborate this preliminary observation and potentially establish the shape of the vertebral articular structure as a diagnosing character of the genus Ophiosabine , more species will have to be examined with respect to their lateral arm plate morphology.

There is no available genus-level name for the group. Verrill (1899b) created the subgenus Ophientodia for O. cuspidata , Ophiacantha scutata Lyman, 1878a and O. pectinula Verrill, 1899a (= echinulata Lyman, 1878a) but didn’t designate a type species. However, as he only reported examining specimens of O. scutata and echinulata it seems improbable that he would have intended O. cuspidata to be the type species. Likewise, he created the subgenus Ophiectodia Verrill, 1899b , without designating a type species, which contained O. enopla Verrill, 1885 , O. rosea and O. spectabilis but only listed material he had examined of O. enopla . Both of Verrill’s proposed subgenera would now be regarded as polyphyletic assemblages.

Etymology. Named using the typical “Ophio” prefix of brittle star genera and after our colleague, ophiuroid taxonomist and friend Sabine Stöhr of the Swedish Museum of Natural History. Gender is feminine.