Sea Stars

Sea stars are composed of a central disc from which arms sprout in radial symmetry. Most starfish have five arms, however some have more or less; in fact some starfish can have different numbers of arms even within one species.

The mouth is located underneath the sea star on the oral or ventral surface, while the anus is located on the top of the animal. The spiny upper surface covering the species is called the aboral or dorsal surface. On the aboral surface there is a structure called the madreporite, which acts as a water filter and supplies the sea star’s water vascular system with water to move.

Additional parts like cribriform organs present exclusively in Porcellanasteridae are used to generate current in the burrows made by these infaunal sea stars.