Is it from harbor? 

Dear collection information can be given with length and weight and substrate where these bivalves are attached on plant/stem of the plant

Dear Dr Asha, Spats could be of  Modeolus. regards, kaladharan

Second picture - Some specimens resemble Modiolus sp., bivalves with line like patterns may be Sunetta sp. 

Not only Modiolus auriculatus and Modiolus sp., other bivalve species  are also there. 

Modiolus spat

Thank you for the feedbacks.

Yes i agree 

Dear Dr. Asha,

I doubt these are spats of oysters!! I see it is attached to seagrass blade. The genus Electroma, a very small bivalve is often encountered in seagrass blades, cages or other hard structures that are in the vicinity for their attachment. Two species are recorded in Indian waters viz. E. alacorvi and E. vexillum. Please send close up image of a single shell both the interior and exterior for easy identification. Until then I keep my fingers crossed.

Best regards

Deepak

I agree with Electroma, likely vexllium. Can you give us close up photographs of the entire inside and outside of one shell?

Thank you for the comments. Soon will do the needful.

Regards