A, anemones, octopus, shrimp and dolphins are all aquatic animals, so they meet the meaning of the question;

B, anemones, squid, spider crabs and snails are not aquatic animals, which does not meet the meaning of the question;

C, spiders in corals, spiders, mussels and squid are not aquatic animals, so they do not meet the meaning of the question;

Grasshoppers, hippos, whales and turtles are not aquatic animals, so they don't meet the problem.

So choose a.