Starfish belong to the kingdom Animalia, the phylum Echinodermata and the class Asteroidea. The order varies depending on the species. The common starfish, Asterias rubens, belongs to the order Forcipultida.
All starfish are marine invertebrates and have bodies composed of a central disc and at least five arms, as well as sticky tube feet that generate hydraulic pressure to allow the starfish to move underwater. Some species are brightly colored, while others are dull brown or blue. Additionally, the skin surface texture varies by species, with some starfish having a smooth surface and others having a spiny or plated surface.