• Perna is commonly known as the ‘Sea mussel’.

• Edible, sedentary, marine mollusc.

• The body of perna is soft and divisible into foot and visceral mass, distinct head is absent.

• Body is enclosed with in a calcareous bivalve shell.

• Shells are hinged together antereo –dorsally by a hinge segment.

• Shell valves are drawn inward and outward by adductor muscles.

• Perna has a ventral pedal groove which leads basally to a byssus cavity.

• Byssus threads helps for attachment to a substratum.

• Vascular – respiratory membrane called plicate membrane.