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Fast Facts Type: Invertebrate Diet: Carnivore Average lifespan in the wild: Up to 35 years Size: 4.7 to 9.4 in. Weight: Up to 11 lbs Did you know? Sea stars have no brains and no blood. Their nervous system is spread through their arms, and their “blood” is actually filtered sea water. Size relative to a tea cup: Echinoderms (“spiny-skinned”) Echinoderms are spiny-skinned invertebrates that live on the ocean floor. The word echinoderm means "spiny skin." No echinoderms are found in fresh water. Modern-day echinoderms have five-fold radial symmetry, having arms or rays in multiples of five. Echinoderms are armored animals that have a hard endoskeleton made of interlocking calcium plates and spines. It is considered an endoskeleton because the plates are covered with a thin layer of “skin.” These slow-moving creatures have a water-vascular system, water-filled channels that go through the body to help with support and movement. The oldest-known fossil echinoderm is roughly 560 million years old! Some echinoderms include sea stars (also called starfish), brittle stars, sea cucumbers, sea urchins, and sand dollars. Sand Dollar Sea Star Dollars Brittle Star Sandare (Starfish) Sea stars, Sea Urchin A bottomechinoderms, dwelling A spiny, disk-shaped another name marine spiny-skinned for starfish, globular animal invertebrate sea bed animals are animals that lives on with long, that have 5-part that live on the ocean floor. the ocean spiny arms. radial floor. symmetry. Many echinoderms use their tube feet to move themselves alone the ocean floor. Starfish use their tube feet to open mollusks, a favorite food.