Description

All adult echinoderms are radially symmetrical. Radially symmetrical means that it is like the spokes on a wheel or like the points on a star. The larvae, though, are bilaterally symmetrical. Sea stars usually have five arms, but some species may have more than fifty arms! Sea stars can regenerate their arms and sea cucumbers can regenerate their internal organs if they have to. For some species of sea stars, the broken limb can grow into another sea star, but on most species, the broken limb will die. The starfish moves around by means of water-vascular systems, suckers, and muscles. The pressure of the circulating water extends the tube feet and the muscles in the feet contract them so that the sea star can creep in a direction. On the tip of a sea star’s arms, it has a light sensitive organ called an eyespot. With it, it can detect light and its general direction and have an idea of where it is going.