Members of the Asteroidea include called true starfish or sea stars. Asteroids are marine invertebrates and are found in all the oceans.

There are about 1,800 known living species of starfish.

Most starfish have 5 arms, although some can have up to 40. In fact some starfish can have different numbers of arms even within one species.

Asteroids can range from less than 2 cm to over 1 m in diameter, although the majority are 12 to 24 cm.

Starfish move using a water vascular system. The tube feet latch on to surfaces and move in a wave, with one body section attaching to the surfaces. Most starfish cannot move quickly.

Numbering in the hundreds on each arm, tube feet also can attach to a food object, such as an oyster or mussel, and open even set of these bivalve shells.

Some species of starfish have the ability to regenerate lost arms and can regrow an entire new arm in time.

Most species are predators, and eating bivalves like mussels, clams, and oysters