It looks like a common backwater clam, Meretrix meretrix...found in Pulicat and Chilka near seaward side. send me the photos to my mail, let me check it again. its difficult to download from RG.
Do you have a better preserved specimen? The documented specimen is damaged/bored and dentition are a bit corroded, which does not allow proper identification.
your right valve specimen is close to a Mactrid under the family Veneridae Rafinisque, 1815. Characteristic of this Genus include the cardinal tooth folded in a furrow and articulating with that of the opposite valve and, accompanying a pit for the ligament (clear in you specimen). Though you have collected the specimen from the mouth of an estuary, it is probably washed ashore.
Ending of the umbo in purple coloration leads it to two possible species viz. Mactra violacea Gmelin, 1791 and M. antiquata Spengler, 1802.
Again, the presence of prominent growth lines towards the ventral margin is interesting.
Based on the shell feaures, it most possilbly be Mactra veneriformis Reeve, 1854. This speies distributes near to the estuary with sandy sediment. Distribution ranges from Japan, Korean and China.
if it is M. veneriformis, then it is probably a NEW RECORD TO INDIA I suppose? is there any literature available pertaining to its distribution in the Indian Ocean?.
Until and unless the specimen is verified I would strictly say no! probably you saw the question that I had raised at the end of my sentence. Possibility!
My curiosity is whether this specimen can have a wider distribution??
We were able to identify a couple of new species of bivalves to the western Indian ocean recently and it was much to our shock and surprise that species absent in the east coast of India was available in the west coast but were not new to eastern Indian ocean.
It is 50% chances of having or not. I think Dr Tenjing has given the sample for dna analysis and will have the results soon. This might throw more light on this species.
It is possible to be M. veneriformis because of the prominent growth lines!!