Ophiurothamnus clausa ( Lyman, 1878 )

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 : 44

Ophiurothamnus clausa ( Lyman, 1878)

Figs 23–24

Ophioceramis clausa Lyman, 1878: 124 , pl. 6 figs 161–163.

Ophiothamnus stultus Koehler, 1904: 141–142 , pl. 25 figs 9–10, pl. 26 fig. 1.

Ophiurothamnus musorstomae Guille, 1981: 427 , fig. 1g –j, pl. 3 figs 20–21.

Ophioceramis clausa – Lyman 1882: 26, pl. 11 figs 4–6.

Ophiurothamnus stultus – Matsumoto 1917: 130. — Koehler 1922a: 104–105, pl. 22 fig. 1–4. — Liao 2004: 149, fig. 78.

Ophiurothamnus clausa – O’Hara & Stöhr 2006: 105, fig. 14 (a–j). — Chen et al. 2020: 651–652, figs 1–2.

Material examined

CHINA • 1 spec.; South China Sea, SE of Hainan Island , seamount; 17°17.60′ N, 111°34.17′ E; depth 1500 m; 2 Apr. 2018; collection event: stn SC021; MSV Shenhaiyongshi leg.; preserved in 95% ethanol; GenBank: MZ 198777 ; IDSSE EEB-SW0023 • 2 specs; 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 -80°C; IDSSE EEB-SW0042 , IDSSE EEB-SW0043 .

Remarks

The disc diameter (4.5–5.0 mm), the circular disc and the morphology are similar to the description of Ophiurothamnus clausa in O’Hara & Stöhr (2006) and to the description from the South China Sea in Chen et al. (2020), but we identified some variability in the number of scales on the dorsal disc and in the shape of the radial shields ( Fig. 23 ). The arm skeleton characters of O. clausa differ from those of other species in the family Ophiacanthidae .

The dorsal arm plate is triangular and well developed ( Fig. 24A ). The arm spine articulation is well developed and has a large muscle opening and a small nerve opening. A volute-shaped perforated lobe is present in most articulations, but is lacking in the dorsalmost one ( Fig. 24B ). A perforation is present on the inner side of each lateral arm plate ( Fig. 24C ). The vertebrae have a long streptospondylous articulation, with broad proximal and distal ends and a narrow middle segment. The proximal end of a vertebra has two clearly separated openings and the distal end of the podial basin becomes short and small. The dorsal side of the vertebrae is distally triangular and proximally flattened, without a keel. The ventral side of the vertebrae has a narrow and straight ambulacral furrow without an oral bridge ( Fig. 24D–G ).

Ophiurothamnus clausa has variable morphological features according to O’Hara & Stöhr (2006), especially regarding the characters of the disc, and the variation in disc covering is very striking, ranging from smooth naked plates to plates with granules, the number and shape of the scales covering the disc, the shape and position of the radial shields and the shape of the arm spines. These character differences cannot be explained by biogeographic distribution or size of the animal ( O’Hara & Stöhr 2006) and may instead be evidence of cryptic speciation.

Distribution

480–3202 m depth. East China Sea, South China Sea, Indonesia, Australia, New Zealand, Kermadec Islands, Philippines, New Caledonia, Papua New Guinea, Mozambique Channel ( O’Hara & Stöhr 2006; OBIS 2021).

Figures

Fig. 23. Ophiurothamnus clausa (Lyman, 1878) (IDSSE EEB-SW0023). A. Dorsal disc. B. Ventral disc. C. Oral frame (SEM). D. Ventral arm (SEM). E. Dorsal arm. F. Ventral arm. Abbreviations: as = adoral shield; asa = arm spine articulation; dap = dorsal arm plate; os = oral shield; ts = tentacle scale; vap = ventral arm plate. Scale bars: A–B = 1 mm; C–F = 500 µm.

Fig. 24. Ophiurothamnus clausa (Lyman, 1878), SEM (IDSSE EEB-SW0023). A. Dorsal arm plate. B–C. Lateral arm plate. B. External view. C. Internal view. D–G. Vertebrae. D. Proximal view. E. Distal view. F. Ventral view. G. Dorsal view. Abbreviations: asa = arm spine articulation; D = dorsal; Dist = distal; mo = muscle opening; no = nerve opening; Prox = proximal; V = ventral; vs = voluteshaped. Scale bars: A, D = 100 µm; B, F–G = 300 µm; C, E = 200 µm.