There are 9,000-15,000 species of sponges. They have existed since the first animal life in the Precambrian era. They are known as the longest living creatures on earth, with a lifespan of approximately 15,000-23,000 years. They are able to live in most habitats, and they feed on small food particles that they filter out of passing water. Sponges are prey to chitons, snails, nudibranchs, turtles, fish, and insects. They are shelter to sea anemones, polychaetas, octopi, copepods, zoanthids, shrimp, brittle stars, amphipods, barnacles, and other fish.

There are approximately 6,000 species of echinoderms within the ocean. Some examples of these species are sea stars/starfish, sand dollars, sea urchins, and sea cucumbers. Echinoderms don't have heads and have 5-point radial symmetry with an endoskeleton made out of calcareous plates, which is often protected by spines. They use a water-vascular system  to gather food and move. They also have hollow, tentacle-like tube feet. Water is drawn into these feet when they expand or contract which allows them to move and 'walk'. Suckers on the tips of their feet are used to hold their prey or attach to a surface. Echinoderms are able to regenerate lost limbs, or even grow a new body from a lost limb.

There are over 110,000 species of Mollusks, including oysters, chitons, clams, snails, slugs, and some squid. They typically have a soft body with a hard shell. Most Mollusks use mucus and cilia to eat, move, and reproduce. Some species of Mollusks have adapted to living on land in humid conditions with the ability to regulate temperature, breathe air, make larger eggs, and maintain moisture levels by conserving water. Some have done the opposite, and have now adapted to living in the water instead of on the  land. These creatures live in all parts of the ocean,  as deep as 9,000 meters down. 

There are approximately 10,000 species of Cnidarians, including corrals, sea anemones, box jellyfish, stalked jellyfish, and more. These are the earliest multicellular life forms known to man. They have a digestive cavity with one opening, and use stinging cells to immobilize their prey and protect themselves against predators. A tissue, known as the ectoderm, covers their outer body and is used to take oxygen directly out of the water. The inner layer of cells called the endoderm, forms the gastrointestinal tracts, respiratory tracts, and inner organs. 

Arthropods include crustaceans and 75% of all animals that are classified as phylum arthropods. They have segmented bodies, jointed appendages, and a hard exoskeleton made of a protein called chitin. Their exoskeleton provides protection and support for the animal's muscles, but once they grow, they will shed their exoskeletons for a new one. 

Crustaceans are a large group of Arthropods found in various habitats. Most are freshwater or marine animals but some are terrestrial, parasitic, and others don’t move. There are over 50,000 known species and they are divided into major groups and sub- categories. The major groups are Brachiopods, Maxillopods, Ostracods, and the Malacostraca. They are then divided into decapods, stomatopods, euphausiids, amphipods, and isopods. Examples include shrimp, crayfish, prawns, crab, and lobster.