An estuary is a semi-enclosed coastal body of waterwhich is connected to the sea either permanently or periodically, hasa salinity that is different from that of the adjacent open ocean due to freshwater inputs, and includes a characteristic biota (Whitfield and Elliott, 2011). According to United States Environmental Protection Agency, an estuarine environment are among the most productive natural habitat on earth, creating more organic matter each year than comparably-sized areas of forest, grassland, or agricultural land. The tidal, sheltered waters of estuaries also support unique communities of plants and animals especially adapted for life at the margin of the sea. The estuarine ecosystem is also one of the most important ecosystems as Estuaries and coastal areas trap significant quantities of material and thus act as filters between land and oceans. More important is the trapping of suspended mud and sand carried by rivers which leads to delta formations around estuaries. The ability of estuaries to remove and to retain materials in suspension and in solution has important practical as well as scientific implications (Schubel, 1984). The high productivity of estuaries is based on their ability to retain detritus material derived from the sea, rivers or salt marshes. Feeding on this detritus are three main taxa of animals, the annelids, the crustaceans and the molluses (McLusky and Elliott, 1981).

India with a huge coastline of 7517 km (ISRO, 2012) which is intercepted by more then 113 major/minor rivers and rivulets, opening on both east and west coast forming huge estuarine habitat (Balasubramanian, 2018). The sub c also harbors some important estuaries of the world like the Hooghly, in Wes Bengal. Most of the Indian's major estuaries occur on the cast coast and larger size in contrast, the estuaries on the west coast. Now a day's estuary gets lo of attention because these areas are amongst the most heavily populated areas throughout the world. The state of Andhra Pradesh got the second longe coastline of 974 km which is next to Gujarat (1600) km among all the maritime states of India (http://mhal.nic.in/par2013/par2013-pdfs/1s-300413/498.pdf)

Mollusca is a major group of animal which are highly diversed, not just in size and in anatomical structure, but also in behaviour and in habitat. The phylum contains some of the most familiar invertebrates, including snails, slugs, clams, mussels, and octopuses. Although most molluses are marine, they have adapted to terrestrial and freshwater habitats all over the planet. They are also found n estuarine ecosystems including shallow sub tidal regions and along the continental shelf. They are vital for a healthy ecosystem and are very susceptible to changes in their environment. Molluscs are also considered excellent ecological indicator as many species are included in the group of bio indicator organisms. Their ecological status provides a window into the health of entire ecosystems. With at least 80,000 known species (Mollusca Base eds, 2020) molluscs are the 2ª most diverse animal group after arthropods. In India, there are 5070 species of molluscs, of these 3371 species are marine molluscs (Alfred, 1998).

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