Marcia H. Adams & A. Adams, 1857

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

Genus Marcia H. Adams & A. Adams, 1857

Type species.

Venus opima Gmelin, 1791

Description.

Moderately sized, outline triangular-ovate to elongate-ovate. Hinge with three cardinal teeth in each valve; posterior and middle cardinal bifid in left valve, middle cardinal bifid in right valve; laterals absent. Ligament external, elongate. Pallial sinus moderately deep, horizontally aligned. Sculpture variable from smooth to commarginal lines to weak commarginal ridges. Often highly and variably patterned externally with bold geometric blotches and radial rays. Inner shell margins smooth.

Remarks.

The species within the genus Marcia are rather variable in form with the sculpture varying from almost smooth ( M. opima ) to finely ridged ( M. japonica and M. hiantina ). Huber (2010) notes this variability and discusses, but rejects, the use of Hemitapes , Römer, 1864 for these more coarsely sculptured forms. All have a horizontally aligned pallial sinus and this contrasts with the steeply ascending orientation seen in Protapes . Furthermore in Protapes the sculpture is stronger with commarginal raised ridges; the posterior margin is obliquely truncated and the anterior pronounced with a depressed lunule.