David Nicholson, age 11, of Lemon Grove, California for his question:
Do starfish lay eggs or bear live young
About 2,000 kinds of starfishes belong to the world ocean. They range in size from half inch midgets to three foot giants. Their various colors range through the rainbow. The number of their arms range from four to 50. The species are so numerous and so different that they could populate a whole zoo of their own. But all the starfishes produce eggs and all of them can regrow new bodies from lost parts.
The starfish’s talent for multiplication is a great problem to fishermen. The tough little creatures devour clams, oysters and other valuable sea foods. One might think that the problem of surplus starfish could be solved by chopping the tough little creatures in half. Not at all. For when sliced in two, both halves can regrow to become two star¬fishes.
This talent for regeneration, or regrowing lost parts, is one of the most amazing wonders of nature. But to oyster fishermen, it is a great nuisance. Scientists have demonstrated that one species can regenerate a complete new body from a half inch section of just one of its five arms.
However, a starfish does not have to wait to multiply until somebody chops him up. We now know that at least some species can pull themselves apart and regenerate new bodies from each of the pieces. Even this is not the complete story. An adult starfish has a pair of male and female organs on each arm.
Once each year, during a definite breeding season, the adults release swarms of male and female cells into the sea. Some species release two million cells in a couple of hours, others release 200 mil¬lion. If all of them merged to form fertilized egg cells that survived, the starfish population explosion would be stupendous. However, most of the cells and fertilized eggs are devoured by fishes and other creatures of the hungry sea.
The fertilized egg is called a zygote. Its two cells multiply by dividing, again and again. After a day or so of this busy multiplication, the zygote becomes a larva. This infant stage of life is a small hollow ball, with surface hairs to propel it through the water. During the next two months, it changes its shape several times.
Unlike its parents, the starfish larva has a two sided body, with front and rear ends. The front end sprouts three tiny arms, while the rest of it takes the form of a five sided starfish. Eventually, the arms latch onto a solid surface and the rest breaks free to become an adult starfish.
This method of multiplication is extremely complicated. One wonders why the larvae must go through a two sided stage of life. Perhaps the answer is lost in ancient history. For most biologists suspect that the modern five sided starfishes descended from two sided ancestors. In this case, the larvae merely develop through ancestral stages.