In Echinoderms, the sexes are separated, but males and females can rarely be determined by external examination. Although some echinoderms brood their young to a certain stage, most of them shed the eggs and sperm into the water through pores to which the sex glands are attached by short ducts. These develop into young echinoderms by going through an extensive and complicated process of metamorphosis, during which the original bilateral symmetry is replaced by a radial symmetry. Many echinoderms can regenerate body parts that have been injured or broken off. In fact, in some kinds a small fragment may regenerate a whole body.
Most Echinoderms are either male or female, although some are hermaphrodites.
In starfish, the sperm or eggs are produced in testes or ovaries, respectively, which fill the arms during the reproductive season. The animals shed their sperm and eggs into the water. Individual starfish detect gametes of their own species in the water, and they respond to that stimulus by releasing their own gametes. Fertilization takes place in open water, and larvae swim around for some time as members of the huge community of plankton that swarm in the ocean. Eventually the larvae, which have bilateral symmetry, swim to the ocean bottom, where they mature and metamorphose into adults that have radial symmetry.