Asteroids

Asteroids, or starfish, are very distinctive echinoderms (see Fig. 7.1). Most have five arms and exhibit the classic echinoderm fivefold symmetry. The mouth and tube feet are positioned on the lower surface. Tube feet are arranged in rows along the arms and the mouth is central (Fig. 7.4). Starfish are voracious scavengers and predators, preying particularly on bivalves. Some species are able to evert their stomach. Specialized tube feet are used to prize the bivalves apart. The stomach then protrudes into the shell digesting the soft tissues inside the shell.

The asteroid skeleton (test) is extremely flexible. It is formed from small calcite plates that are not tightly sutured together. Therefore, the test disarticulates rapidly after death and identifiable fossil starfish are very rare.

Starfish have been important predators for most of the Phanerozoic. Starfish predation may be responsible for the failure of brachiopods to re-radiate after the end-Permian mass extinction.

Madreporite: perforated plate associated with the

Madreporite: perforated plate associated with the

and prising open bivalve shells

Fig. 7.4 Vertical section of a starfish.

and prising open bivalve shells

Fig. 7.4 Vertical section of a starfish.

Was this article helpful?

0 0
Survival Basics

Survival Basics

This is common knowledge that disaster is everywhere. Its in the streets, its inside your campuses, and it can even be found inside your home. The question is not whether we are safe because no one is really THAT secure anymore but whether we can do something to lessen the odds of ever becoming a victim.

Get My Free Ebook


Post a comment