The term "marine invertebrates" is used to describe animals found in a marine environment which are invertebrates: lacking a notochord. In order to protect themselves, they may have evolved a shell or a hard exoskeleton, but this is not always the case.

As on land and in the air, invertebrates make up a huge portion of all life in the sea. Invertebrate sea life includes: jellyfish, corals, shrimp, crabs, flatworms, starfish, sea urchins, sponges, shellfish, squid, tunicates, etc..