The Thondi coast of Palk Bay is one among the biospheres which is biologically rich and rated among the highly productive regions of the world. Its diversity is considered globally significant. However, the diversity of this area is poorly documented, especially that of molluscans associated with the seaweeds and sea grasses occurring here in great profusion. In the present investigation, eleven different seaweeds and four species of seagrasses were recorded; the highest molluscan species with its percentage contribution in both seaweeds and seagrasses were recorded as Cerithedia cingulata (49.40%), Umbonium vestiarium (16.09%), Bullia belangeri (14.05%), Nassarius comptus (1.98%) and Babylonia zeylanica (1.46%).