Many crustaceans (for example, lobsters, shrimp, and crayfish) use their tails to swim, but crabs have reduced tails that curl under their shells and are not used in swimming. this is an example of . natural selectionb. an adaptationc. a homologous structured. a vestigial trait

a vestigial trait

Explanation:

Vestigial trait is a characteristic that is present in an organism but not used for the intended purpose. For example: vestigial organs. These structures are in their rudimentary form and almost degenerated because they are not required anymore by the organism.

Many crustaceans use their tails to swim and hence have functional fully formed tails. However crabs usually walk on ocean beds. Crabs that do swim have modified rear legs. Hence, there is no requirement of a functional tail in crabs making it a vestigial trait. As a result, the tail is reduced and curled under their shells.

this is a good question! i'll do some research and come back when i have the answer!