subaquatic

/ˌsʌbəˈkwætɪk/

A subaquatic creature lives or exists entirely under water. A squid cruising the ocean depths or a clam buried in the seabed both fit the bill.

Subaquatic creatures like octopuses, jellyfish, and starfish spend their whole existence below the surface. The word often shows up in marine biology texts, but you might also see it describing things like subaquatic caves or plants. Subaquatic is derived from the Latin sub, "under," and aquatic, "relating to or operating in water."

Definitions of subaquatic

1. adjective

   growing, living, or remaining under water
   synonyms: subaqueous, submerged, submersed, underwater

   aquatic

   operating or living or growing in water