Ophiactis cf. brachygenys H. L. Clark, 1911

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, European Journal of Taxonomy 810 (1), pp. 1-95 : 68-74

Ophiactis cf. brachygenys H. L. Clark, 1911

Figs 40–42

Ophiactis brachygenys H.L. Clark, 1911: 135–137 , fig. 51. Ophiactis definita Koehler, 1922a: 187–189 , pl. 64 figs 1–2, 7.

Ophiactis definita – Koehler 1930: 121. — Guille 1981: 439.

Ophiactis brachygenys – Irimura 1991: 80. — Liao 2004: 228–229, fig. 134.

Material examined

CHINA • 1 spec.; South China Sea , SE of Zhongsha Islands, seamount; 13°58.65′ N, 114°52.09′ E; depth 1550 m; 25 Sep. 2020; collection event: stn SC013; MSV Shenhaiyongshi leg.; preserved in 95% ethanol; GenBank: MZ 198769 ; IDSSE EEB-SW0015 • 1 spec.; same collection data as for preceding; GenBank: MZ 198770 ; IDSSE EEB-SW0016 .

Description (IDSSE EEB-SW0015)

MEASUREMENTS. Disc diameter 5.8 mm, heptamerous specimen.

DiSC. Robust and sub-pentagonal, heptamerous ( Fig. 40A–B ). Dorsal disc covered by large, coarse, irregular, polygonal overlapping scales, denser in disc center ( Fig. 40A ). Radial shields large, broad, internal margin straight, external margin convex, pointed proximal angle, longer than wide, half disc radius long, completely separated by a single series of two or three plates ( Fig. 40D ). Ventral disc also covered by small, irregular, overlapping scales. Genital slits conspicuous and extending from oral shield to disc periphery ( Fig. 40C ). Oral shield spearhead-shaped, with wide proximal angle, wider than long ( Fig. 40F ). Adoral shield larger than oral shield, pair proximally connected, proximal edge concave, three times as long as than wide, slightly narrowing distally, bordering proximal edges of oral shield, not separating oral shield from arm ( Fig. 40F ). One large, wide, rectangular ventralmost tooth with tricuspid edge. Single large, broad (wider than teeth), axe-shaped, operculiform lateral oral papilla, covering second tentacle pore inside mouth angle ( Fig. 40F ). Some oral papillae more pointed laterally or tricuspid ( Fig. 40B, F ).

ARMS. Dorsal arm plate slightly fan-shaped, large, slightly convex distally, wide proximal angle, as long as wide and mostly separated ( Fig. 40G ). First ventral arm plate small, triangular with truncated distal end. Second ventral arm plate tetragonal or pentagonal, wider than long, connected to first ventral arm plate, then pentagonal with straight to concave distal edge, round proximal angle along arm and mostly separated ( Fig. 40B, H ). Three arm spines on most segments, with thickened base, rounded, blunt tip, 1–1½ arm segment in length, middle one longest ( Fig. 40G–H ). One large, broad, oval tentacle scale, half as long as ventral arm plate, covering pore completely ( Fig. 40H ).

COLOR. Wet specimen light brown, dry disc light grey and dorsal arm light brown or pink ( Fig. 40 ).

OSSiCLE MORPHOLOGY.Extracted from heptamerous specimen, lateral arm plate with three well-developed spine articulations formed by two subparallel, bent, separated lobes, unequal in size. Two similarly sized openings for muscle and nerve ( Fig. 41A–C ). Vertebrae with well-developed zygospondylous articulation, narrow, shallow dorsal furrow, not extending beyond distal articulating structures, deep ambulacral groove, widened distally, large podial basins ( Fig. 41D–H ).

Remarks

According to our specimens, Ophiactis cf. brachygenys is a fissiparous species and these are the first records of specimens with more than five arms (confirmed by molecular data, see below). Six- and seven-armed specimens had similar morphological features. However, the hexamerous specimen (2.8 mm disc diameter) differs slightly from the heptamerous specimen in the number of arms, the widely separated radial shield, the first one to two arm segments having four arm spines but only on one or two arms, and a smooth, pointed disc spine near the periphery of the disc ( Fig. 42 ).

The holotype description of O. brachygenys is similar to both specimens from the present study, except for the number of arms and completely separated radial shields.

H.L. Clark (1911) mentioned that one of his specimens (9 mm disc diameter) had distally separated radial shields, the dorsal arm plate was shorter and wider, and both dorsal and ventral arm plates were more closely together. Also, it had a few short disc spines at the periphery of the ventral disc (H.L. Clark 1911). These variations concur with the specimens from the present study ( Figs 40–42 ). Ophiactis definita was synonymized with O. brachygenys by Liao (2004). The description of O. definita is similar to that of O. brachygenys , but Koehler (1922a) described some morphological differences between the two species. Ophiactis brachygenys from the present study and the description of its holotype (H.L. Clark 1911) are morphologically distinguished from the type of O. definita by having separated dorsal arm plates along the arm, wider than long and not as broad radial shields, and wide as long oral shields. In addition, the radial shields are proximally and distally separated, and disc spines are present on the ventral disc ( Figs 40A , 42K, M ). Molecular analysis of both species from different localities suggests that these morphological variations may be species specific (see below).

Distribution

216–1550 m depth. Recorded from the Lubang Islands near the Philippines, East China Sea, southeast Japan, Indonesian seas, Coral Sea, Solomon Sea, Bismarck Sea and Timor Sea ( OBIS 2021).

Figures

Fig. 40. Ophiactis cf. brachygenys H.L. Clark, 1911 (IDSSE EEB-SW0015 = heptamerous specimen). A. Dorsal disc. B. Ventral disc (first and second ventral arm plates highlighted). C. Lateral disc. D. Radial shields. E–F. Oral frame (operculiform lateral oral papillae highlighted). G. Dorsal arm. H. Ventral arm. Abbreviations: as = adoral shield; dap = dorsal arm plate; gs = genital slit; os = oral shield; rs = radial shield; tp = tentacle pore; ts = tentacle scale; vap = ventral arm plate. Scale bars: A–B = 1 mm; C–E, G–H = 500 µm; F = 200 µm.

Fig. 41. Ophiactis cf. brachygenys H.L. Clark, 1911, SEM (IDSSE EEB-SW0015 = heptamerous specimen). A–C. Lateral arm plate (internal, external). D–H. Vertebrae. D. Proximal view. E. Distal view. F. Ventral view. G. Dorsal view. H. Lateral view. Abbreviations: D = dorsal; Dist = distal; dl = dorsal lobe; mo = muscle opening; no = nerve opening; Prox = proximal; V = ventral; vl = ventral lobe. Scale bars = 300 µm.

Fig. 42. Ophiactis cf. brachygenys H.L. Clark, 1911 (IDSSE EEB-SW0016 = hexamerous specimen). A. Dorsal disc. B. Ventral disc. C. Radial shields. D. Lateral disc. E. Disc spine. F. Oral frame. G. Dorsal arm. H. Ventral arm. Abbreviations: as = adoral shield; dap = dorsal arm plate; ds = disc spine; gs = genital slit; os = oral shield; rs = radial shield; tp = tentacle pore; ts = tentacle scale; vap = ventral arm plate. Scale bars: A–B = 500 µm; C–H = 200 µm.