Question

Unio is-
A. Edible oyster
B. Marine shellfish
C. Freshwater mussel
D. Sea mussel

Answer 1

Hint: An aquatic organism inhabits swamps, lakes, ponds, and rivers. Typically, they burrow by their large ventral muscular foot in the mud at the bottom of the pond.

Complete answer:
Option A is incorrect. Oyster is the common name for a variety of separate families of bivalve salt-water molluscs living in marine or brackish environments. The valves are highly calcified in some species, and many are very irregular in shape. They are usually eaten cooked or raw and are known as a delicacy in some countries. Some types of pearl oysters are harvested within the mantle for the pearl produced.
Option B is incorrect. The term refers mainly to marine animals, edible invertebrates of freshwater such as crayfish and river moulds are also often grouped under the umbrella word "shellfish." While they can vary in shells, all shellfish are invertebrates. They are "marine" in an informal context, as non-mammalian species that spend their whole life in water.
Option C is correct. Unio is a genus of freshwater musts, molluscs in the Unionidae tribe, the river molluscs. It is also called bivalve. It is a triploblastic species possessing a true coelom.
Option D is incorrect. Mussel is the generic term from saltwater and freshwater environments used by members of many bivalve mollusc families. In particular, these groups have a shell with an elongated and asymmetric shape compared to other edible clams, often more or less oval or rounded.

So, the correct answer is Option C.

Note:
The bivalve shell is bound together by the muscles of the anterior and posterior adductors, and the retractor muscles will open it. Protractor muscle while burrowing pushes the foot. Gills or ctenidia are wide and composed of two-gill plates under the mantle flaps on each side of the body. They are in control of both the respiratory and the collection of food.