Complete question:
Question: A species of crayfish that lives in caves produces eyestalks like its above-ground relatives, but no eyes (unlike its above-ground relatives). Eyestalks in these cave-dwelling crayfish are an example of
a. An evolutionary error
b. A dominant mutation
c. Biogeographical evidence of evolution
d. A vestigial trait
Answer:
Vestigial traits.
Step-by-step explanation:
Vestigial traits or the vestigial structures are the ones that were/are fully functional in the ancestors or relative species of the organisms. However, those traits or structures are not in working conditions in these organisms now. In the given example, crayfish is said to be a cave dweller.
In caves, organisms can not use eyes to see. Therefore this crayfish species do not develop functional eyes but retain the eye-stalks that otherwise carried the functional eyes in its relative species. This makes the "presence of eyestalks" a vestigial trait in this species.