Marine Invertebrates are those animals which lack a notochord, a characteristic of vertebrates. Therefore, in order to protect themselves, they usually have a shell or a hard exoskeleton, but not always!

P: Porifera (Sponges)

P: Cnidaria (Jellyfish, Corals, Hydroids)

P: Ctenophora (Comb Jellies)

P: Mollusca (Clams, Snails, Octopi)

P: Arthropoda (Crabs, Shrimp, Lobsters, Copepods)

P: Echinodermata (Sea Stars, Brittle stars)

Marine worms (Polychaeta, Vestimentifera)