Answer:
The correct answer is - sea cucumber.
Step-by-step explanation:
Hydra, aurelia, and sea anemone belong to Phylum - Coelenterata or cnidaria while sea cucumber is a member of echinoderms. Cnidaria is radially symmetrical, free-swimming or fixed, aquatic and solitary or colonial animals. While sea cucumber are animals like starfish or sea urchin.
They found on the seafloor and have pentaradial symmetry however, developes bilateral symmetry later.