Invertebrates, animals without backbones, occur on land and in the water, making up over 95% of the animal species on earth. Marine invertebrates are a diverse group of over 50,000 species including crustaceans, such as crabs, shrimp, and lobsters; cephalopods, including octopus, squid, and cuttlefish; mollusks, including oysters, clams, and snails; jellyfishes; corals; sea stars; sponges; just to name a few. With so many different kinds of marine invertebrates, it is easy to see that they occupy a broad diversity of habitats around the world, ranging from intertidal zones, to estuaries, to deep seas.

Marine invertebrates are some of the most sought after foods for human consumption, providing a healthy source of protein and much enjoyment. Included in this group are the shrimp, crabs, and lobsters, which make up much of the fare at popular seafood restaurants. Also included are squid, octopus, clams, and mussels.

Marine invertebrates range in size from the giant squid, featured in 20,000 Leagues Under the Sea, to tiny organisms less than a single millimeter long. As an animal without a backbone, many marine invertebrates protect themselves with a hard exoskeleton, or outer shell, such as those found on sea snails, oysters, and clams. However, quite a number of marine invertebrates do not have a hard exoskeleton. How, then, do they protect themselves? Many of them have developed defense mechanisms, such as the stinging cells (nematocysts) of jellyfish. Sea slugs are often brightly colored, but when a fish or other organism attempts to eat this attractive food item, they find the taste to be unpalatable. Cone shells, a marine snail, are notorious for their poisonous sting.