Which term refers to a sea urchin?

• A. Gastropoda
• B. Echinoidea
• C. Ectotherm
• D. Gill Membranes

Answer: (B)

Taxonomic grouping: sea urchins are classified in Echinoidea, a class of echinoderms that includes the spiny, radially symmetric animals with a calcareous test and a water vascular system. Gastropoda is a mollusc class that includes snails and slugs, not sea urchins. Ectotherm describes an organism’s temperature regulation, not its classification. Gill membranes are a respiratory feature not used for naming sea urchins; they mainly respire through diffusion across body surfaces and the water vascular system. So, the term for a sea urchin is Echinoidea.