It is an echinoderm, which means it belongs to a group of animals known for spiny skin. That group also includes sea urchins and sea cucumbers. Sea stars belong to the scientific class called Asteroidea, which means star form. Their cousins, the brittle and basket stars, belong to the Class Ophiuroidea, which means serpent tail in appearance. A sea star is not a fish because, among other things, it does not have a backbone.
Fish are vertebrates, as are mammals, including humans.
Sea stars use the suction cups on the tips their many feet not only to move but to capture their meals. If a sea star loses a part of its arms, it can grow it back. Sea stars normally have five arms, although some species may have more. The arms come together in the middle of the animal, forming a central disc. The arms, in most cases, are triangular in shape.