Ophiactis modesta Brock, 1888

Peyghan, Soroor, Doustshenas, Babak, Nabavi, Mohammad Bagher, Rounagh, Mohammad Taghi, Larki, Amir Ashtari & Stöhr, Sabine, 2018, New records of the brittle stars Ophiothela venusta and Ophiactis modesta (Echinodermata: Ophiuroidea) from the northern Persian Gulf, with morphological details, Zootaxa 4527 (3), pp. 425-435 : 431-432

Ophiactis modesta Brock, 1888

Fig. 5

Ophiactis modesta Brock, 1888: 482 ; Balinsky 1957: 14, A. M. Clark & Courtman-Stock 1976: 163, Irimura 1981: 22, Liao & A. M. Clark 1995:216.

Material examined: 36 specimens, northern Persian Gulf , port of Bushehr, on sponges on shipwrecks, May 2015 and May 2016 .

Size range: Disc diameter 1.5–4 mm, arm length 6–13 mm.

Description: 6 arms (whole animal hexamerous), disc circular, dorsally covered by coarse, round scales, bearing few short, smooth, pointed spines, denser at the disc margin ( Fig. 5A ). Almost completely separated radial shields, half as long as disc radius, meeting at distalmost end, with white patch distally. Oral shield spearheadshaped to rhombic, with distal lobe. Multiple madreporites (3 in fig. 5B) of similar shape to oral shield, with single distal hydropore. Adoral shields curving around lateral edges of oral shields, distolaterally flaring. A single, large, operculiform oral papilla on the junction of oral plate and adoral shield, covering the second tentacle pore inside the mouth angle ( Fig. 5B ). Wide, tricuspid teeth. Dorsal arm plates contiguous, about twice as broad as long, rounded hexagonal in shape ( Fig. 5C ). Ventral arm plates hexagonal, wider than long, contiguous/overlapping ( Fig. 5D ). Single, round tentacle scale, covering the tentacle pore. Arm spines 4, minutely thorny, thick and blunt, middle one longest, about as long as an arm joint. Colouration of live specimens green with regular white spots.

Depth distribution: Found at 2 m and 15 m in this study.

Geographic distribution: Indo-Pacific including the Indian Ocean ( Dahihande & Thakur 2017), Gulf of Thailand and Andaman Sea ( Putchakarn & Sonchaeng 2004), Africa ( Balinsky 1957), Western Australia ( Marsh & Morrison 2004), Japan ( Murakami 1963), Hawaii ( MacKay 1945).

Remarks: In this study, individuals were found in large densities inside an unidentified sponge. It was found on subtidal hard bottoms, artificial reefs and intertidal areas. This species is easily mistaken for O. savignyi , and Cherbonnier & Guille (1978) regarded O. modesta as a mere colour variant of O. savignyi . However, as noted by A.M. Clark & Courtman-Stock (1976), the radial shields are smaller (shorter than the disc radius) than in O. savignyi (longer than the disc radius) and the single oral papilla is much larger in O. modesta and round to oval in shape. Sometimes O. savignyi has 2 oral papillae but they are always quite small.

Figures

FIGURE 5. Ophiactis modesta from the Persian Gulf. A, dorsal disc. B, oral frame. C, dorsal arm. D, ventral arm. Abbreviations as in fig. 4, and DAP, dorsal arm plate, TS, tentacle scale. Scale bars in millimetre.