Mussel is the common name used for members of several families of bivalve molluscs, from saltwater and freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other edible clams, which are often more or less rounded or oval. The word "mussel" is frequently used to mean the bivalves of the marine family Mytilidae, most of which live on exposed shores in the intertidal zone, attached by means of their strong byssal threads ("beard") to a firm substrate.
From all animals of water we are allowed to eat :
1. Fish which has or had scales on it. Fish which has no scales at all are not allowed to eat.
2. Shrimps or prawns.
All other water animals e.g. crab, oyster, shells, lobster, ink fish etc is not allowed to eat.