Richard E. Strassberg earned his Ph.D. in East Asian Studies from Princeton University.
Starfish are marine invertebrates. They typically have a central disc and five arms, though some species have a larger number of arms. The aboral or upper surface may be smooth, granular or spiny, and is covered with overlapping plates.bout 1,500 species of starfish occur on the seabed in all the world's oceans, from the tropics to frigid polar waters. They are found from the intertidal zone down to abyssal depths, 6,000 m (20,000 ft) below the surface.
1 Sea stars are more commonly referred to as starfish. 2  They are related to sea cucumbers: both are echinoderms, which means âspiny-skinned.â All echinoderms have five-part radial symmetry. 3  An active sea star can travel one mile in about a week. 4  If a sea star loses an arm, it can quickly grow a new one.