Ophiacantha vorax Koehler 1897

Ophiacantha vorax Koehler, 1897 Figs 29–30 Ophiacantha vorax Koehler, 1897: 353–356, pl. 8 figs 68–69. Ophiacantha anchilabra H.L. Clark, 1911: 204–206, fig. 95. Ophiacantha vorax – Koehler 1899: 62, pl. 7 figs 52–54; 1922a: 63, pl. 15 figs 4–5. — Liao 2004: 122–123, fig. 59. Ophiacantha anchilabra – H.L. Clark 1915: 196. — Matsumoto 1917: 117. Material examined CHINA • 1 spec.; South China Sea, SE of Hainan Island, seamount; 17°59.21′ N, 111°01.17′ E; depth 1500 m; 1 Apr. 2018; collection event: stn SC020; MSV Shenhaiyongshi leg.; preserved in -95°C ethanol; GenBank: MZ 198765, MZ 203267; IDSSE EEB-SW0011 • 1 spec.; South China Sea, SE of Hainan Island, sea plain; 18°26.13′ N, 111°49.09′ E; depth 1576 m; 26 Jun. 2019; collection event: stn SC001; MSV Shenhaiyongshi leg.; preserved in -80°C; GenBank: MZ 198766, MZ 203268; IDSSE EEB-SW0012 • 1 spec.; South China Sea, SE of Hainan Island, seamount; 17°17.60′ N, 110°34.18′ E; depth 1500 m; 2 Apr. 2018; collection event: stn SC021; MSV Shenhaiyongshi leg.; preserved in -80°C; IDSSE EEB-SW0045. Description (IDSSE EEB-SW 0011) MESUREMENTS. Disc diameter 6.2 mm. DiSC. Sub-pentagonal, covered by skin with underlying scales, bearing four to six short, stump-like spines with crown of sharp, straight thorns and a few elongated thick, thorny stumps in the center (Fig. 29A–F). Radial shields long, narrow, widely separated, slightly convex, distal end thickened and exposed (Fig. 29A). Radial shields concealed by thin skin and thorny stumps, but clearly visible through skin when specimen dried (Fig. 29A). Dorsal arm plate on first arm segment covered by thorny stumps (Fig. 29D). Ventral disc also covered by thorny stumps, but less dense than on dorsal disc, scales clearly visible, genital slits short (Fig. 29F). Oral shield triangular, much wider than long, distal end slightly convex, proximal edges concave or straight (Fig. 29B), madreporite larger, as long as wide, distal edge strongly convex (Fig. 29G). Adoral shields narrow, curved, three times as long as wide and not separated, bordering proximal edges of oral shield, not separating it from arm (Fig. 29G). Jaws elongated, with one large pointed ventralmost tooth and three long, spiniform, pointed lateral oral papillae on each side, distalmost papilla wider than other two (Fig. 29G). ARMS. Dorsal arm plates triangular, distal edge convex, separated (Fig. 29I). Ventral arm plate on first arm segment small, wider than long, slightly triangular with concave distal edge. Second ventral arm plate pentagonal, wider than long, with obtuse proximal angle, excavated lateral edges and slightly convex distal edge. Following plates as wide as long, distalwards becoming wider than long, slightly hexagonal, with curved distal edge and angular proximal edges, separated except on second arm segment (Fig. 29H, J). Lateral arm plates meeting above and below. Six smooth arm spines, three dorsal and three ventral. Dorsalmost arm spine one and a half to two arm segments in length, second dorsalmost arm spine longest and meeting across dorsal midline (Fig. 29I–J). Ventral arm spines similar in length, with finely thorny surface (Fig. 29K). One elongated tentacle scale, large, often as long as ventral arm plate (Fig. 29H). COLOR. When alive, entire specimen light brown, darker brown when dry (Fig. 29). OSSiCLE MORPHOLOGY.Arm spine articulations well-developed, placed at an angle on separate, protruding distal part of lateral plate, bordered by a wavy ridge, middle articulations largest (Fig. 30A–B). Arm spine with thorny surface (Fig. 30C). Volute-shaped perforated lobe in most articulations, reduced in dorsalmost articulation, with large muscle opening and small nerve opening (Fig. 30A–B). Vertebrae with short, well-developed zygospondylous articulation with a broad, shallow dorsal furrow, distally abruptly truncated, podial basins wider than long (Fig. 30D–H). Ambulacral groove widely diverging distally, without oral bridge (Fig. 30H). Remarks The holotype description of the dorsal disc of Ophiacantha vorax (5 mm disc diameter) is slightly different from conditions in our specimen, which has no elongated disc stumps. However, this morphological feature was only found here on one of the 3 specimens collected. Variability in morphological characters (arm spines, extent of thorny stumps on radial shields, tentacle scale) is low in O. vorax (Koehler 1922a). Koehler (1897) considered one of the distinguishing features of O. vorax to be the presence of only six arm spines, but H.L. Clark (1911) and Liao (2004) documented eight to nine arm spines in their specimens. Therefore, the number of arm spines is not a suitable character to distinguish O. vorax from other species of Ophiacantha. Ophiacantha pentagona Koehler, 1897 is related to O. vorax, but differs in having long and thicker oral papillae, strongly moniliform arms and longer ventral arm plates in the middle region of the arm. Ophiacantha vorax closely resembles O. longidens Lyman, 1878 in the shape of the oral papillae and oral shields, as well as in the disc shape, but differs in the arrangement of arm spines, and the shape of the arm plates and tentacle scales. Ophiacantha longidens has flattened arm spines, blunt with a thorny surface. Another species resembling O. vorax is O. duplex Koehler, 1897, recorded from deep waters in Japan, Philippines, Indonesia, Australia and Madagascar. It can clearly be distinguished by its large tentacle scale, less thorny, long, thin arm spines, large dorsal arm plate and the presence of large disc spines, as well as the smaller thorned spines. Distribution 550–1908 m depth. South China Sea, East China Sea, off East Japan, India, Philippines, Indonesia, Makassar Strait and Molucca Sea, Coral Sea and New Zealand (OBIS 2021).
Published as part of Nethupul, Hasitha, Stöhr, Sabine & Zhang, Haibin, 2022, New species, redescriptions and new records of deep-sea brittle stars (Echinodermata: Ophiuroidea) from the South China Sea, an integrated morphological and molecular approach, pp. 1-95 in European Journal of Taxonomy 810 (1) on pages 53-57, DOI: 10.5852/ejt.2022.810.1723, http://zenodo.org/record/6419522
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