Detailed Instructions: Given a scientific passage and an answer, generate a question for the given answer.
Problem:Passage: Echinoderms are named for their "spiny skin. " However, the spines aren't on their skin. They are part of the endoskeleton. The endoskeleton consists of calcium carbonate plates and spines, covered by a thin layer of skin. Adult echinoderms have radial symmetry . This is easy to see in the sea star and sand dollar in Figure above . However, echinoderms evolved from an ancestor with bilateral symmetry. Evidence for this is the bilateral symmetry of their larvae. Answer: echinoderms
Solution:
What are named for their "spiny skin"?