Ophionereis ( Ophiotriton ) boucheti, O’Hara & Thuy, 2025

O’Hara, Timothy D. & Thuy, Ben, 2025, Seamount ophiuroids from the High Seas of the western Indian Ocean, Zootaxa 5718 (1), pp. 1-88 : 75-78

Ophionereis ( Ophiotriton) boucheti sp. nov.

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Fig. 27

TYPE LOCALITY. Walters shoal, Zone sommitale Sud, 33° 15.053´S, 43° 54.4771´E, 26 m

TYPE MATERIAL. — MD208 : stn WS06,Walters shoal, Zone sommitale Sud, 33°15.053´S, 43°54.4771´E, 26m, 1/5/2017, holotype: 1 ( MNHN IE.2016.1342); paratypes: 2 ( MNHN IE.2023.4170) ( DNA code= IE.2016.1342) .

OTHER STUDY MATERIAL. — MD208 : stn WR01, Walters shoal, Zone sommitale Sud-Ouest, 33° 12.18´S, 43° 50.828´E, 36 m, 30/4/2017: 1 ( MNHN IE.2016.1350) . — MD208 : stn WB05 , Walters shoal, Zone sommitale Sud, 33° 15.12´S, 43° 54.514´E, 26–30 m, 1/5/2017: 2 ( MNHN IE.2023.4157) . — MD208 : stn WS07, Walters shoal, Zone sommitale Sud, 33° 15.435´S, 43° 52.1851´E, 30–33 m, 2/5/2017: 1 ( MNHN IE.2016.1358) . — MD208 : stn WS08, Walters shoal, Zone sommitale, Sud-Est, 33° 13.722´S, 43° 55.8861´E, 30–33 m, 3/5/2017: 1 ( MNHN IE.2023.4171) . — MD208 : stn WB09 , Walters shoal, Zone Sommitale Nord Ouest, 33° 13.767´S, 43° 55.7751´E, 27–30 m, 4/5/2017: 4 ( MNHN IE.2023.4166) .

COMPARATIVE MATERIAL EXAMINED. Ophionereis cf. intermedia Mayotte, Recif Nord, 12° 35.964´S, 45° 5.994´E, 0–2 m, 9/1959, identified by Cherbonnier & Guille (1978) as Ophionereis hexactis, MNHN EcOs 21707. SAYA/YB05, Saint Brandon, 16° 28.97´S, 59° 42.66´E, 12 m, 19/11/2022, MNHN IE.2023.4380 ( DNA code=IE.2023.4380). SAYA/YS12, NE Saya de Malha, 10° 22.75´S, 62° 7.75´E, 26 m, 9/11/2022, MNHN IE.2023.4410 ( DNA code=IE.2023.4410). Ophionereis cf. variegata Ilot Tanikely , near Nosy Be, 17/3/1960, identified by Cherbonnier & Guille (1978) as Ophionereis degeneri, MNHN EcOs 21706; identified by Cherbonnier & Guille (1978) as Ophionereis degeneri, MNHN EcOs 21705. Ophionereis dubia (J. Müller & Troschel, 1842) : Pulau Pinang, Malaysia, 5° 22.7´N, 100° 6.9´E, 13.6 m, 12/9/2005, NSMT E5543 ( DNA code=TIM032). Scottburgh, Aliwah Shoal, 30° 16.034´S, 30° 49.07´E, 12–17 m, 15/11/2016, MV F237926 ( DNA code=Aliwah1). ATIMO VATAE/TR02, 25° 1.3´S, 47° 0.5´E, 17 m, 29/4/2010, MNHN IE.2007.4724 ( DNA code=TOH255-IE.2007.4724). KGR/Sled11, King George River region, 13° 54.291´S, 127° 19.7315´E, 11 m, 7/6/2013, MV F193495 ( DNA code=F193495). Koyo2014/16, E of Mago-jima Island, Ogasawara, 27° 11.878´N, 142° 12.843´E to 27° 12.346´N, 142° 12.625´E, 126.5–128.9 m, 25/6/2014, NSMT E10208 ( DNA code=NSMT E10208). SAYA/YB07, Saint Brandon, 16° 48.622´S, 59° 29.88´E, 7 m, 20/11/2022, MNHN IE.2023.4205 ( DNA code=IE.2023.4205). SAYA/YR05, NW Saya de Malha, 10° 37.2´S, 60° 10.3´E, 39 m, 6/11/2022, MNHN IE.2023.4298 ( DNA code=IE.2023.4298). Ophionereis hexactis (H.L. Clark, 1938) : Ashmore /18, Ashmore Reef, Blue Grotto, SW of Middle Island, 12° 16.42´S, 123° 0.71´E, 2–6 m, 7/10/2002, MV F93671 ( DNA code=MVF93671). Ophionereis semoni Döderlein, 1896 : KGR/ AS 03, King George River region, 13° 48.957´S, 127° 19.2864´E, 73 m, 12/6/2013, MV F193497 ( DNA code=F193497). Ophionereis tigris H.L. Clark, 1938 : UF/HI09-003, Heron Island, Wistari Reef, 23° 27.113´S, 151° 52.027´E, 11–13 m, 11/11/2009, UF 9889 ( DNA code=UF9889).

COMPARATIVE MATERIAL NOT EXAMINED. Ophionereis intermedia (A.M. Clark, 1953) : Magari , Notojima Island, Ishikawa Pref., Japan, 37° 9´N, 136° 59´E, 1.5–2 m, 4/3/2003 , NSMT E5055 ( DNA code= TIM021 ). Ophionereis thryptica ( Murakami, 1943) : 2008 , NSMT E-2172-p01 ( DNA code= TIM050 ) .

Diagnosis. Small body size (to 2.2. mm dd). Disc covered in minute overlapping scales, without enlarged scales around the margin, small widely separate radial shields not covered by scales. No genital papillae. Five arms, supplementary DAPs 2/3 as long as the primary DAP, 3 rounded arm spines with blunt tip, middle one only slightly longer than the others. Thin brown bands across the distal end of white radial shields.

Description. Holotype 2.2 mm dd, arms 13 mm long, disc covered in minute overlapping scales, 0.05–0.08 mm wide, no obvious primaries, marginal disc scales not enlarged, exposed section of radial shields 0.2 mm long, 2x as long as wide, widely separate, aligned to each side of the arm base, continuing proximately under the disc for another 0.2 mm; disc scales not continuing onto dorsal arm; ventral scales similar size, obscured by skin near oral shields; no granules or spines along wide genital slit; oral shields broadly triangular with rounded angles, widest distally, adoral shields narrowly triangular, with an acute proximal angle and a widened concave distal edge, just touching or separate interradially, radially separated by the small 1st VAP, oral and adoral shields minutely beaded; 4 broad teeth with convex or obtusely-angled hyaline edges, ventralmost smallest; 4 oral papillae, the inner three (infradental, buccal shield, and 2nd adoral shield spine) are oval, often pointing proximally, adoral shield spine is plate like, a little separate, and larger than the others, the thin Lyman’s ossicle forms the distal rim of the 2nd oral tentacle pore, which opens into the jaw slit.

Arms five, thin, DAPs hexagonal, basal plates as wide as long, widest proximally (almost triangular), becoming thinner and widest near the mid-length of the plate, contiguous; supplementary plates not contiguous, start at the widest point of the main DAP, and widen into a triangular plate distally confluent with the main DAP; first VAP much smaller than the rest, triangular to rhomboid, widest distally, succeeding VAPs contiguous, 1.5x as long as wide, with convex distal edge, rounded distolateral corners, concave lateral sides and an obtuse angle proximally, minutely beaded, becoming wider distally than proximally, 3 arm spines, round in cross-section, slightly tapering towards a blunt apex, subequal and as long as a segment near the arm base, middle one becomes a little longer than the others at mid-arm; single oval tentacle scale, 1.5x as long as wide, 1/2 the VAP in length.

Colour (preserved): disc light yellow-brown, with darker patches near the arm base and sometimes around the lateral disc area, radial shields lighter colour, so that the dark patch appears to be divided into 3 sections, ventral disc surface also darker, which continues to a variable extent across the oral shields, first dorsal arm segment light, rest of the arm greenish-brown with thin dark transverse lines every 3–6 segments, these lines are often wider near the edge of the arm than the centre; arms also banded ventrally, 1–2 dark segments alternating with 3–6 light segments, base of arm spines also dark adjacent to dark segments.

Paratypes and other material ( 1.5–3 mm dd), smallest specimens with thin brown bands across the distal end of radial shields, some specimens with pale patches in the centre of the ventral disc area, and darker colours on the oral plates, others with pale areas next to the genital slits, some with the bases of all arm spines coloured. Paratype (IE.2023.4170) ossicles: LAPs higher proximally then distally, with nodulated surface, arm spine articulations composed of two straight parallel lobes, with a smaller knob proximally between them, muscle and neural perforation sit between the lobes; arm spine minutely thorny with vertical grooves near the spine apex; vertebrae zygospondylous.

Distribution. Walters shoal ( 26–36 m).

Remarks. There are a group of Ophionereis species which have discs covered with very fine plates or skin, large supplementary DAPs that are typically as long as the primary DAP, and (excepting O. intermedia ) lack granules/ spines along the genital slits. We propose to utilise the subgenus name Ophiotriton Döderlein, 1896 for this group of species. Döderlein (1896) created this taxon for his new species O. semoni and defined it by the presence of skin rather than plates covering the disc. However, we expand this narrow definition to include all Ophionereis species with very fine disc plating and no genital granules, including O. dubia ( Müller & Troschel, 1842) , O. hexactis H.L. Clark, 1938 , O. thryptica Murakami, 1943 , and O. tigris H.L. Clark, 1938 . We have representatives of all these species in this clade on our phylogeny. To this list could be added O. amoyensis A.M. Clark, 1953 , O. andamanensis James, 1982 , O. vivipara Mortensen, 1933a and O. sexradia Mortensen, 1936 , although we have not examined specimens of these species. Ophionereis sexradia from the Canary Islands is fissiparous, as are some small specimens from Japan (H.L. Clark 1911, fig. 79g) that possibly represent undescribed species. In addition, the Ophiotriton clade with these species on our tree also contains a sample from a small Japanese specimen of O. intermedia A.M. Clark, 1953 that differs in having a row of small sharp separated spines running along the genital slit. Similar 5-armed specimens also occur in the Indian Ocean (erroneously reported as O. hexactis by Cherbonnier & Guille, 1978), which are divergent from the Japanese O. intermedia in our phylogeny, and which we designate as O. cf. intermedia pending formal description. The widespread ‘species’ O. dubia is also polyphyletic on our tree and appears to contain cryptic species. There are numerous synonyms (A.M. Clark 1953, Irimura 1982). More DNA samples are required to sort out species boundaries and nomenclature in this taxon, including from the Red Sea, type locality for O. dubia .

The new species O. boucheti is distinguished by its small size, 5 arms, covering of tiny disc plates except over the small radial shields, lack of genital granules, and colour scheme. It is closest in form to O. dubia and O. vivipara . Small specimens of O. dubia (at least a small Australian specimen, MV F109865, that has the colour scheme of synonym O. stigma H.L. Clark, 1938) have DAPs as wide as long, with large glassy supplementary DAPs that are contiguous along the arm. The VAPs are hourglass-shaped, 2x as long as wide, incised laterally around the tentacle pores. The dark colour across the radial shields is a thin ‘Y’-shaped band that forks proximally. Ophionereis vivipara , a brooding species from the intertidal of Mauritius, is also a small species (to 3 mm dd) that has non-contiguous supplementary DAPs, but differs in having characteristic star-shaped markings on the centre of the disc. The type figures also show extremely small scales on the dorsal and ventral disc surfaces ( Mortensen 1933a).

Specimens from Madagascar and the Comoro Islands, referred by Cherbonnier & Guille (1978) to the species O. degeneri A.H. Clark, 1949 , are mis-identified. An examination revealed enlarged marginal plates adjacent to the radial shields and a small accessory LAP between the arm segments laterally, a characteristic of the species Ophionereis variegata Duncan, 1879 not O. degeneri (see Matsumoto 1917 fig 79, A.M. Clark 1953).

Etymology. Named after Dr Philippe Bouchet (Muséum National d’Histoire Naturelle, Paris) a principal investigator of the MD208 expedition.

Figures

FIGURE 27. (a–d) Ophionereis (Ophiotriton) boucheti sp. nov. holotype MNHN IE.2016.1342 (a) dorsal, (b) ventral, (c) whole body, (d) lateral view of arm base; (e–h) paratype MNHN IE.2023.4170 (e) exterior view of lateral arm plate, (f) interior view of lateral arm plate, (g) distal view of vertebra, (h) arm spine.