In a tide pool, a student encounters an organism with a hard outer covering that contains much calcium carbonate, an open circulatory system, and gills. The organism could potentially be a crab, a shrimp, a barnacle, or a bivalve. The presence of which of the following structures would allow for the most certain identification of the organism?

a. a heart

b. a filter-feeding apparatus

c. a mantle

d. a body cavity

e. eyes

Answer is C

Explanation:

The mantle is specific to bivalves, as molluscas The mantle plays an important role in the life of molluscas as it encloses the mantle cavity, which is a space found between the mantle and the body wall and houses the gills or lungs. The mantle secretes the shell, specifically through it's epithelial cells

Bivalves as molluscas are found in marine and freshwater habitats and possesses an hard outer covering of calcium Carbonate, a feature also present in crabs, shrimps and barnacles.

Bivalves also possesses an open circulatory system with a heart and vessels, a feature also present in Crabs, shrimps and barnacles.

Some crustaceans (which crabs and shrimps are part of) are filter feeders. They however uses cilia and create water current from the beating of their appendages. Bivalves use cilia as filter feeders too.

Crabs, barnacles, shrimps and bivalves possesses body cavities as eucoelomates with their coelem limited.

They may also possesses gills for gaseous exchange.