Ophiotreta eximia ( Koehler, 1904 )

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 : 31-34

Ophiotreta eximia ( Koehler, 1904)

Figs 15–16

Ophiacantha eximia Koehler, 1904: 116–117 , pl. 21 figs 3–5.

Ophiacantha dilecta Koehler, 1904: 117–118 , pl. 22 figs 3–4.

Ophiotreta eximia – H.L. Clark 1915: 216. — Koehler 1922a: 70–71, pl. 8 figs 5–6, pl. 93 fig. 7. — O’Hara & Stöhr 2006: 55–56, fig. 4e–g.

Ophiotreta dilecta – H.L. Clark 1915: 216. — Koehler 1922a: 71.

Material examined

CHINA • 1 spec.; South China Sea, SE of Hainan Island , seamount; 17°35.80′ N, 111°02.00′ E; depth 1750 m; 3 Apr. 2018; collection event: stn SC022; MSV Shenhaiyongshi leg.; preserved in -80°C; IDSSE EEB SW0030 .

Description ( IDSSE EEB-SW 0030)

MEASUREMENTS. Disc diameter 11.9 mm, arm width 3.0 mm.

DiSC. Circular, dorsal side covered by overlapping scales with one or mostly two spines ( Fig. 15A–B ). Disc spines tall, 0.4–0.6 mm high, 10–11 times as high as wide, slender, thorny, with two to three small, non-flaring terminal thorns ( Fig. 15C–G ). Few disc spines scattered on first dorsal arm segment ( Fig. 15E ). Radial shields covered by disc scales and skin ( Fig. 15A, E ). Ventral disc completely covered by disc spines, two small disc spines at ventralmost margins of three oral shields. Genital slits conspicuous, extending from oral shield to periphery of disc ( Fig. 15B–F ). Oral shield much wider than long, broadly triangular, with obtuse proximal angle and lobed or convex distal edge. Adoral shield long and narrow, mostly not separated. Adoral shields enclosing proximal edges of oral shield and separating it from first lateral arm plate, reaching just beyond lateral angle of oral shield ( Fig. 15F ). Jaws longer than wide. Cluster of papillae on jaw with three to five large, pointed, spiniform tooth papillae on dental plate and two rows of pointed papillae on apex of jaw (on oral plates), with large, pointed tip, five to seven lateral oral papillae and distalmost two flat and enlarged ( Fig. 15F ).

ARMS. Dorsal arm plates as long as wide, fan-shaped, triangular with straight proximal end, slightly curved distal margin, covered with minute spines and consecutive plates completely separated ( Fig. 15J ). Ventral arm plates pentagonal, as wide as long except on first one to two arm segments, straight obtuse triangular proximal end, distal margin truncated to concave, along arm plates thickened distalwards, consecutive plates well separated ( Fig. 15H–I ). Lateral arm plates meeting above and below ( Fig. 15H ). 10–12 arm spines at each lateral arm plate; five to six upper arm spines four to six arm segments in length, smooth and meeting across dorsal midline ( Fig. 15G ); five to six lower arm spines short, two to three shortest, half arm segment in length, thorny ( Fig. 15K ). Lowermost arm spine on lateral arm segments slightly flattened with curved shape and straight, elongated thorns along tip of curved surface ( Fig. 15H ). One elongated, large tentacle scale with thorny apex, longer than ventral arm plate but becoming narrow and pointed distalwards on arm ( Fig. 15K ). First arm segment with two tentacle scales covering tentacle pore ( Fig. 15F ).

COLOR. When alive, grey to whitish on disc and arms, mouth region and spines light brown ( Fig. 15A–B ).

OSSiCLE MORPHOLOGY. Arm spine articulations well developed and placed at small angle in relation to distal edge of lateral arm plate, separated from proximal part of plate by wavy ridge. Ventral and dorsal articular lobes fused into a single volute-shaped articular structure (with sigmoidal fold, see Martynov 2010), dorsal lobe perforated by small holes, ventral lobe smooth and non-perforated ( Fig. 16A ). Large muscle opening and small nerve opening, but dorsalmost arm spine articulation without sigmoidal fold and ventral ones entire but connected to main part of lateral arm plate by short ridge ( Fig. 16A–B ). Vertebrae with long zygospondylous articulation, distally abruptly truncated, dorsal median furrow moderately expressed and podial basins long and large ( Fig. 16C–G ).

Remarks

The disc diameter of our specimen is within the range of the type specimens (11–21 mm). Koehler (1904) divided these specimens according to morphological variation of the arm plate and arm spines, but these variations fall within the morphological type series of O. eximia , and little morphological variation is expressed in the number of arm spines, height of the disc spines and number of oral papillae. The size of the specimens affects the morphological variation in O. eximia such as the number of oral papillae, the number of tentacle scales on the first arm segment and disc spine length. Due to these morphological variations, it is rather difficult to distinguish species of Ophiotreta . Ophiotreta matura Koehler, 1904 is quite similar to O. eximia , but differs in having stouter disc spines with flared terminal thorns, thornier upper arm spines and arm plates and hook-shaped thorny ventralmost arm spines ( O’Hara & Stöhr 2006). The specimen in the present study showed a unique morphological feature in two small thorny spines located at the ventral margin of the oral shields directly proximal to the genital slits ( Fig. 15F ).

Distribution

724–1893 m depth. South China Sea, New Zealand, Makassar Strait, Sulu Sea, Molucca Sea, Flores Sea, Coral Sea and Tasman Sea ( O’Hara & Stöhr 2006; OBIS 2021).

Figures

Fig. 15. Ophiotreta eximia (Koehler, 1904) (IDSSE EEB-SW0030). A. Dorsal disc. B. Ventral disc. C–D. Disc spines. E. Dorsal view of arm base. F. Oral frame (yellow circle = tentacle scales on first tentacle pore; red circle = oral shield spine). G. Lateral view of arm base. H. Ventralmost arm spine. I. Ventral arm. J. Dorsal arm. K. Ventral arm spines. Abbreviations: as = adoral shield; dap = dorsal arm plate; ds = disc spine; os = oral shield; ts = tentacle scale; vap = ventral arm plate; vas = ventral arm spine. Scale bars: A–B = 2 mm; C–D, F, H = 200 µm; E, G, I–K = 1 mm.

Fig. 16. Ophiotreta eximia (Koehler, 1904), SEM (IDSSE EEB-SW0030). A–B. Lateral arm plate. C–G. Vertebrae. C. Proximal view. D. Distal view. E. Ventral view. F. Dorsal view. G. Lateral view. Abbreviations: D = dorsal; Dist = distal; dl = dorsal lobe; mo = muscle opening; no = nerve opening; Prox = proximal; V = ventral; vl = ventral lobe; vs = volute-shaped. Scale bars: A–D = 300 µm; E–G = 500 µm.