Echinoderms have separate sexes, male or female, although some are hermaphroditic. The males and females discharge their eggs and sperm through broadcast spawning into the water where they are fertilized. Fertilization is external; the gametes are simply shed into the water. A female can release one hundred million eggs at once. The floating embryo develops into a ciliated, free-swimming, bilaterally symmetrical larva, which undergoes radical metamorphosis into the radial symmetrical adult. In some species, the whole digestive system is changed during metamorphosis, and the organism acquires a new mouth and anus. Regeneration is achieved by means of asexual binary fission. If a piece of certain echinoderms is cut off or injured, their great ability to regenerate quickly creates a new body part or even a new echinoderm can grow.
No comments:
Post a Comment