The isopod is some Sphaeromatidae species. An almost similar question in researchgate recently with interesting answers

https://www.researchgate.net/post/Identification_of_Isopod_Anyone_can_help_ID_this_species

Concerning the bivalve I think that it looks like Musculus costulatus.

Thank u

 1. So far the Bivalve is concern I am sure with Genus i.e. Musculus ,but species level identification is not sure unless a complete image is not observed.

Thank u

The isopod is some Sphaeromatidae species. An almost similar question in researchgate recently with interesting answers

https://www.researchgate.net/post/Identification_of_Isopod_Anyone_can_help_ID_this_species

The bivalve is Musculista senhousia the crustacean are Isopods but i don't know the genus

Durga,

The isopods are definitely sphaeromatids, but unfortunately, I can not help you with Indian Ocean genera or species.  The larger specimen looks like an adult, and the smaller one a juvenile.  Be careful to use several specimens when you try to identify these with a key.  Some sphaeromatid genera (e.g. Cilicaea) show strong sexual dimorphism; the abdomen and uropods are quite different in the adult males and females, so you want to be sure to have some of both for ID purposes.

 bivalve specimen is most properly Musculus costulatus that lives attached  in intertidal marinewater 

Thank u sir