Starfish

Any marine invertebrate of the class Asteroidea (phylum Echinodermata) with rays, or arms, around an unclear central disc is known as a sea star. They are not fish, despite their former common name. The estimated 1,600 live species of sea stars can be found in all oceans, with the highest diversity in the northern Pacific. The majority of species are 20 to 30 cm (8 to 12 inches) across; but, some are as little as 1 cm (0.4 inch) and others as large as 65 cm (25 inches).Sea star arms are hollow and covered with small spines and pedicellariae (pincerlike organs) like the disc; on the lower side are grooves with rows of sucker-tipped or pointed tube feet (see video of tube foot anatomy and physiology). One or more of a sea star's arms can be lost and replaced. It can move in any direction and stick to steep surfaces thanks to its tube feet.