Sea stars have no brains and no blood. Their nervous system is spread through their arms and their blood is actually filtered sea water. The beloved starfish’s common name with sea star because, well, the starfish is not a fish. It’s an echinoderm, closely related to sea urchins and sand dollars. There are some 2,000 species of sea star living in all the world’s oceans, from tropical habitats to the cold seafloor. The five-arm varieties are the most common, hence their name, but species with 1