Mike Woods, age il, of Nogales, Ariz., for his question:
IS THE STARFISH REALLY A FISH?
A starfish is a sea animal that has armlike extensions on its body. Starfish live in all of the world's oceans but they are not fish. They are members of a group of animals called echinoderms. The echinodern group also includes the sea cucumber, sea lily and the sea urchin.
Most kinds of starfish have five "arms" and look live five pointed stars. However, not all starfish look this way. Some of them have such short arms that their bodies look like pentagons, or five sided shapes. Others, called sun stars or sea stars, have many arms.
The starfish's mouth is in the middle of the underside of the central disk and it leads directly into a large baglike stomach. On the outside of the body, a groove extends from the mouth to the tip of each arm. Rows of slender tubes, called tube feet, line these grooves.
The animal uses the suction disk at the end of each tube foot for crawling. These disks grip hard surfaces. The starfish "sees" with small colored eyespots that are located at the tips of each arm. The eyespots sense light but they cannot form images.
The starfish uses its tube feet and a tiny, sensitive tentacle located at the tip of each arm to "feel."
Starfish release eggs into the sea through small holes between their arms. The eggs form into tiny swimming larvae. After a while, each larva settles down on the sea bottom and develops into a starfish.
Starfish can regenerate or again grow new arms when the old ones are broken off. Even if a starfish is cut in two, each of the pieces will regenerate into a new animal. Most starfish live for three to five years, but some may live as long as seven years.
Many starfish feed on shelled animals such as mussels, clams and oysters. The starfish can push its stomach out through its mouth.
When a starfish feeds on an oyster, it attaches its tube feet to the two halves of the oyster's shell and pulls the shell halfs apart. By opening a tiny crack, the starfish can reach the oyster within the shells.
When the starfish has opened the oyster's shell a bit, it pushes its stomach, turned inside out, through the crack and into the oyster's shell.
A starfish can slide its stomach through a crack no larger than the thickness of a piece of cardboard. The stomach surface surrounds the oyster's soft body, slowly digests it and absorbs the food into the starfish's body.
Such starfish, as you can well imagine, are serious pests in the oyster breeding grounds of the East Coast of the United States.
A starfish's upper surface is covered with a hard, coral like shell.
Some types of starfish have as many as 50 arms.