Marcia opima (Gmelin, 1791)

Arathi, Anitha R., Oliver, P. Graham, Ravinesh, Raveendhiran & Kumar, Appukuttannair Biju, 2018, The Ashtamudi Lake short-neck clam: re-assigned to the genus Marcia H. Adams & A. Adams, 1857 (Bivalvia, Veneridae), ZooKeys 799, pp. 1-20 : 4-5

Marcia opima (Gmelin, 1791) Figure 3

Original combination.

Venus opima Gmelin, 1791

Synonyms.

(from MolluscaBase 2018b) Venus pinguis Chemnitz, 1782 (unavailable), Venus nebulosa Gmelin, 1791; Venus triradiata Gmelin, 1791; Venus gravida Röding, 1798; Tapes ceylonensis G. B. Sowerby II, 1852.

Type locality.

As the name Venus pinguis Chemnitz, 1782 is unavailable, this species takes the name of Venus opima Gmelin, 1791, both names referring to Chemnitz, 1782 tab. 34, figs 355-357. The type locality is given as East Indian Seas by Chemnitz (1782) but as India by Gmelin (1791).

Material examined.

Ashtamudi Lake, Kerala, 21 live collected specimens + 26 articulated conjoined valves.

Measurements.

Length 30.4-48.6 mm, mean L/H = 1.3, mean L/B = 1.6.

Description.

Shell equivalve, relatively thin; inflated, umbos prominent. Outline triangularly subovate, inequilateral, beaks slightly in front of midline. Lunule well defined, prominent, flattened, and broad. Escutcheon weakly defined. Shell surface smooth, glossy with faint growth lines. Adductor muscles of equal size. Pallial sinus horizontally aligned, broadly rounded, extending to midline of shell. External colouration variable and variously patterned, shades of brown, cream and dark grey with 3-4 radial darker bands. Internal colouration white.

Distribution.

Marcia opima is distributed throughout the Indian Ocean from the Red Sea to Indonesia. Authentic records are from East Africa, Kenya, Djibouti, Yemen, Arabian Gulf, Oman, Pakistan, India, Sri Lanka, Myanmar, Andaman Sea, West Malaysia, Penang, and Sulawesi ( Huber 2010).

Remarks.

Marcia opima was originally described from India and it has a wide distribution on the east and west coasts of India including the Andaman-Nicobar and Lakshadweep islands ( Ramakrishna and Dey 2010, Subba Rao 2017). A fishery for this spe cies in the Ashtamudi Lake was reported by Appukuttan et al. (1985) but we cannot confirm the actual identity of the species involved. Other fisheries of this species are recorded by Subba Rao (2017), in particular at Ratnagiri (west coast) and Adyar River (east coast).