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 symmetry (they are pentameral), having arms or rays in multiples of five. Echinoderms are armored animals that have a hard exoskeleton made of interlocking calcium carbonate plates and spines. Some echinoderms include sea cucumbers, sea urchins, sea stars and feather stars, which have a soft body surrounded by upwards-facing arms.
