Starfish

With their perfectly shaped and attractively colored bodies, starfish are reminders of happy seaside vacations.

Starfish are the most generally viewed parts of the echinoderms; the spiny-skinned animals. All echinoderms have five-sided bodies, and this shape can be seen in many starfish. When grown-up, the body of a typical starfish is drawn out in five rays, or arms, radiating from a central point.

The tube feet are arranged in paired rows on the undersides of the rays and are used for moving about and getting prey. The mouth is on the underside, and the rear-end is on the top of the midway part of the body.

A Variety of Shapes

Although many starfish have five large rays shaped like a classic star, some are cookie shaped with a pentagonal outline. Some are wafer thin, others are plump. Some even have more than five rays; generally multiples of five, but occasionally odd numbers like seven or twenty-three. Some of the pentagonal types are less predatory. Organic food particles land on their upper surface and are carried to the mouth by cilia.

Some starfish feed on corals, smothering the polyps with their stomachs. Others catch and eat fish. One Pacific starfish uses pedicellariae to trap small fish. The fish settles for a moment on the bottom, touching the starfish. The pedicellariae snap shut, catching the fins, and the fish is trapped and slowly engulfed.