What is another word for underwater creature?

Here are some other words for underwater creature, depending on the specific context you're using it in:

General:

* Aquatic animal

* Marine life

* Sea creature

* Ocean dweller

* Subaquatic inhabitant

Specific:

* Fish (for creatures with gills and fins)

* Mollusk (for creatures with a soft body and a shell, like snails and clams)

* Crustacean (for creatures with a hard exoskeleton, like crabs and lobsters)

* Cnidarian (for creatures with stinging tentacles, like jellyfish and corals)

* Echinoderm (for creatures with a spiny skin, like starfish and sea urchins)

More poetic:

* Sea dweller

* Deep-sea denizen

* Water sprite

* Ocean wanderer

The best word to use will depend on the specific context of your writing or conversation.