An invertebrate is basically an animal that is lacking a vertical support system in their structural makeup, for example a backbone or notochord. Almost all of the earths living animal species are filed under the invertebrate distinction. Only 3% of the living animals that travel the vast earth are considered vertebrates. They fall under the Chordate subphylum of Vertebrata. Vertebrates most commonly include mammals, birds, reptilians, fish species, and also amphibians. Invertebrates encompass over 30 phyla (phylums, greek for clans) and range from the basic sea cucumber through flatworms, mollusks, corals, and even include arthropods like crabs. Invertebrates are found on land and in sea and if it is a living animal and it is not a reptile, amphibian, mammal, bird, or fish it is very highly likely it is an invertebrate.

Other common underwater animals that fall under invertebrate are flatworms, crustaceans, bryozoa, jellyfish, snails, sponges, coral, worms, squid, starfish, sea urchins, hydras, anemones, lobsters, crabs, sea barnacles, brittle stars, octopus, ribbon worms, shrimp, lobsters, crayfish, sand dollars, and many more species.