A) Feather star — Crinoidea (V): Crinoids are marine animals that include feather stars. B) Acorn worm — Enteropneusta (IV): Acorn worms are hemichordates belonging to Enteropneusta. C) Pearl oyster — Bivalvia (I): Pearl oysters are mollusks under class Bivalvia. D) Millipede — Diplopoda (III): Millipedes are arthropods in the class Diplopoda.