Question

Which one of the following features in a fossil shell of Pelecypod indicates the burrowing habit of the animal?

• A. Pallial sinus
• B. Ligamental groove
• C. Adductor impression
• D. Dentition

Hint:

Pallial sinus in bivalves usually indicates siphon-bearing and burrowing habit.

Answer 1

The Correct Option is A

Concept:
Pelecypods, also called bivalves, may live as burrowing organisms. Their shell features help identify their mode of life.

Step 1: Understand pallial sinus.
Pallial sinus is an inward bend in the pallial line of a bivalve shell.

Step 2: Relation with burrowing habit.
Burrowing bivalves have long siphons. These siphons need space for retraction inside the shell. \[ \text{Long siphons} \Rightarrow \text{Pallial sinus} \]

Step 3: Final conclusion.
Therefore, pallial sinus indicates burrowing habit in pelecypods. \[ \therefore \text{Correct Answer is (A)} \]