Ophiomoeris obstricta ( Lyman, 1878 )

Parameswaran, Usha V., Nowshad, B. Mohammed, Dixit, Sudhanshu, Manjebrayakath, Hashim, Idreesbabu, K. K. & Saravanane, N., 2020, New records of brittle stars (Echinodermata: Ophiuroidea) from the Lakshadweep atolls, northern Indian Ocean, with notes on Indophioderma ganapatii Sastry Marimuthu & Rajan, 2019, Zootaxa 4809 (3), pp. 560-570 : 562-563

Ophiomoeris obstricta ( Lyman, 1878)

( Fig. 2 a-f)

Ophioceramis (?) obstricta Lyman, 1878: 124–125 , pl. 6 (164–166).

Ophioceramis (?) obstricta — Lyman 1882: 26–27, pl. 11 (1–3).

Ophiomoeris obstricta — Koehler 1904: 17; 1922: 38–39, pl. 5 (3–4); 1930: 55.— Matsumoto 1917: 140.— O’Hara & Stöhr 2006: 120–123, fig. 16(A–G).

Ophiomoeris spinosa Koehler, 1904: 17–18 , pl. 4 (1–3).— Koehler 1922: 40; 1930: 55–56.

Ophiurases obstrictus H. L. Clark, 1911: 250–252 , fig. 122.

Ophiomoeris projecta Matsumoto, 1915: 65 .— Matsumoto 1917: 141–143, fig. 35.— McKnight 1975: 70; 1993: 174, 187.— Imaoka et al. 1991: 124, fig. 47.

Ophiomoeris parva H. L. Clark, 1939: 39–41 , fig. 4–5.

Ophiomoeris inflata A. H. Clark, 1949: 15–17 , fig. 5.

Material examined: Kavaratti Island—Seawater tank of NIOT Desalination Plant, collecting water from ~ 350m depth (10° 34.44’ N, 72° 38.40’ E), coll. M. Nowshad on 12.12.2019, 4 specimens ( CMLRE IO /SS/ECD/00234, 00235; MTRL /DST/E0301, E0302) .

Description: D.d. 2–3 mm, disc deeply incised interradially and sunken centrally; arms noded and coiled ventrally below the disc. Central primary plate distinct, surrounded by smaller, polygonal scales; these scales are fewer in smaller specimens ( Fig. 2 b-c). Radial shields large, 1/3 of d.d., distinctly petal-like—elongate with a rounded distal margin, having a gentle but distinct groove centrally with abradial margin gently curling upwards; pairs separated proximally by 1–2 wedge-shaped radial plates and contiguous distally (completely separated by a single row of plates in IO/SS/ECD/00235); rounded conical granules present on a few or all disc plates and sometimes along inner edge of radial shields ( Fig. 2 b-c). Ventral inter-radial areas small, skin-covered and embedded with small scale-like plates, some of which are somewhat tumid and granule-like ( Fig.2c ). Genital slits small but distinct, more or less vertical ( Fig. 2e ). Oral frame as wide as long; oral shields fan shaped, 1.5 times wider than long ( Fig. 2e ). Adoral shields more or less crescent shaped, not separating oral shield from first ventral arm plates. Ventralmost tooth rounded conical; ventrolateral edge of oral plate bearing spaced papillae in the following configuration—one infradental papilla and one (occasionally two) lateral oral papilla—both pointed with rugose margins, along with one short and rounded adoral shield spine ( Fig. 2e ). Dorsal arm plates fan shaped with rounded distal margin, wider than long basally, separated from each other throughout ( Fig. 2d ). Ventral arm plate very thin, oblong, twice as wide as long, with a notched distal margin; first few intact, subsequent plates fragmented ( Fig. 2f ). Lateral arm plates elongate, broadly in contact dorsally and ventrally, separating dorsal and ventral arm plates throughout. Arm spines conical, two at the first segment, up to six at subsequent segments and decreasing to three distally; dorsal-most spine longest, as long as segment; ventral-most spine half this length, transformed into hooks towards the arm tip ( Fig. 2f ). A single, minute, spine-like tentacle scale present on first two segments ( Fig. 2f ).

Colour: Cream with light or white mottling on the disc and arms.

Distribution: Madagascar, Comoros, Maldives, India ( Lakshadweep), Indonesia, Papua New Guinea, New Caledonia, Philippines, Vanuatu, Australia, New Zealand, Japan, Hawaii; 35-1100m ( OBIS, 2020a).

Biological association: The specimens were found attached to an unidentified gorgonian ( Fig. 2a ).

Remarks: O’Hara & Stöhr (2006) synonymised Ophiomoeris spinosa Koehler, 1904 , O. projecta Matsumoto, 1915 , O. parva H. L. Clark, 1939 and O. inflata A. H. Clark, 1949 with O. obstricta Lyman, 1878 after extensive examination of type and other materials. The characters of the present specimens fall within the range of variations documented for the expanded O. obstricta and they are herein assigned to this species. The characters of the present specimens match with the type description of O. parva H. L. Clark, 1939 , collected off the nearby Maldives Islands, except for the relatively longer proximal arm spines and complete lack of granules in the latter, which O’Hara & Stöhr (2006) considered to be juvenile characters. O’Hara & Stöhr (2006) suggest that the wide range of morphological variation in Ophiomoeris obstricta may be indicative of a cryptic species-complex, which can be resolved only with molecular analysis of a wide range of specimens from across its distribution range.

Figures

FIGURE 2. Ophiomoeris obstricta, a, b, d: IO/SS/ECD/00234, c: MTRL/DST/E0301, e-f: IO/SS/ECD/00235. (a) live specimen, ex situ, (b, c) disc, dorsal view, ventro-lateral interradii indicated with arrows, (d) proximal arm, dorsal view, (e) SEM of disc, ventral view, and (f) SEM of proximal arm, ventral view, location of ventral arm plates indicated with arrows. Scale bar: 1mm (a-c) and 0.5mm (d-f).