Ophiophthalmus Matsumoto, 1917

Nethupul, Hasitha, Stoehr, Sabine & Zhang, Haibin, 2022, Review of Ophioplinthaca Verrill, 1899 (Echinodermata, Ophiuroidea, Ophiacanthidae), description of new species in Ophioplinthaca and Ophiophthalmus, and new records from the Northwest Pacific and the South China Sea, ZooKeys 1099, pp. 155-202 : 155

Genus Ophiophthalmus Matsumoto, 1917

Type species.

Ophiacantha cataleimmoida H. L. Clark, 1911

Included species:

Ophiophthalmus normani (Lyman, 1879)

Ophiophthalmus relictus (Koehler, 1904)

Ophiophthalmus hylacanthus (H. L. Clark, 1911)

Diagnosis.

Adapted from Matsumoto (1917), H. L. Clark (1911), Lyman (1879), Paterson (1985), and Koehler (1904, 1922). Disc rounded to sub-pentagonal, and covered by irregular overlapping disc scales with sparse to coarse minute granules. Radial shields ovoid, naked, and widely separated by disc scales with granules. Three or four spiniform lateral oral papillae, with one ventralmost tooth at jaw apex. Dorsal arm plates contiguous at arm base then separated. Ventral arm plates pentagonal to tetragonal, and separated. Four to seven arm spines at each lateral arm plate. Arm spines smooth to rugose, one to three arm segments in length, thick, with blunt tip. Mostly single, large, flat, oval tentacle scale.

Distribution and habitat.

100-2194 m depth, North Pacific, Australia, New Zealand, Papua New Guinea, South Africa. Substrate of mud, fine grey sand, Foraminifera, and small stones ( Olbers et al. 2019).

Remarks.

Ophiophthalmus was created by Matsumoto (1917) for species, which at the time were included in the genera Ophiomitra , Ophiomitrella , and Ophiacantha . However, Paterson (1985) noted that the ophiuroid genus Ophiophthalmus is a junior homonym of a reptilian genus described by Fitzinger (1843). Some later works ( Olbers et al. 2019; Okanishi et al. 2021) used the name Ophiophthalmus in quotation marks, indicating its invalid status, while other works (Suppl. material 1) seem to have been oblivious to the issue, causing confusion and taxonomic instability. Article 23.9.1 of the International Code of Zoological Nomenclature ( International Commission of Nomenclature 2000), states that "prevailing usage of a name must be maintained when the senior homonym has been used as a taxon’s presumed valid name, in at least 25 works, published by at least ten authors in the immediately preceding 50 years and encompassing a span of not less than ten years". In the present case, the 50-year period extends from 1971 to 2021 and 25 publications by more than ten authors have been found in this period (Suppl. material 1).

Both names are available, because they have been published with either a description or mention of a type species, and they satisfy articles 10, 11, and 12 of the Code. Fitzinger (1843) proposed the reptile’s name Ophiophthalmus as a replacement name for Lialis Gray, 1834 with the same type species L. burtonis Gray, 1835, immediately making Ophiophthalmus Fitzinger, 1843 a junior synonym of Lialis ( Shea 2021). Fitzinger’s contemporary colleagues and later researchers rejected his proposed name change, and Ophiophthalmus was thus never used for a reptile and cannot be used in the future, because it lacks a type species separate from Lialis . Instead, prevailing usage of the name Ophiophthalmus Matsumoto, 1917 has been shown here and it must be maintained.

Ophiophthalmus belongs to one of the largest and diverse ophiuroid families, Ophiacanthidae in the order Ophiacanthida, and is delineated from most other genera by having minute granular coverage of the disc, smooth and somewhat finely serrated arm spines, ovoid radial shields, and by characters of the arm plates ( Koehler 1904, 1922; H. L. Clark 1911; Matsumoto 1917; Paterson 1985; Liao 2004; Martynov et al. 2015; Olbers et al. 2019). Currently, Ophiophthalmus includes four species: O. cataleimmoidus , O. hylacanthus , O. normani , and O. relictus . The genus Ophiomitra is closely resembles Ophiophthalmus by having ovoid, separated radial shields, and smooth, long arm spines, but differs in a thorny tip on granules or stumps, 10-16 oral papillae at the jaw, up to nine arm spines ( Lyman 1869; Lütken and Mortensen 1899; H. L. Clark 1911; Matsumoto 1917; Koehler 1922; Olbers et al. 2019). Matsumoto (1917 b) suggested that contiguous dorsal arm plates on the arm base, and the proximal arm spines not arranged in a fan shape can be used to distinguish Ophiophthalmus from Ophiomitrella , whereas Koehler (1922) distinguished these from each other by naked radial shields and overlapping disc scales, but Paterson (1985) observed that these characters are not consistent among all species within these genera. However, H. L. Clark (1911) mentioned that Ophiophthalmus species were remarkably consistent in some specific characters (he examined more than 4,000 specimens). Recent molecular studies suggested that Ophiomitrella may be polyphyletic in the family Ophiacanthidae , and species from this genus need to be revised ( Christodoulou et al. 2019).