About Sea Star .........10分呀!!!!!!

Starfish are marine invertebrate belong to Kingdom Animalia, Phylum Echonodermata, Class Asteroidea. They exhibit radial symmetry.They typically have five or more "arms " which radiate from an indistinct disk (pentaradial symmetry).Starfish possess a hydraulic water vascular system that aids in locomotion. The water vascular system has many projections called tube feet, on the ventral face of the starfish's arms, which function in locomotion and aid with feeding.
Most species are generalist predators, some eating clams, and oysters.Some species are detritivores, eating decomposed animal and plant material, or organic films attached to substrate.

There are about 1,800 known living species of starfish, and they occur in all of the Earth's oceans. The greatest variety of starfish is found in the tropical Indo-Pacific. Areas known for their great diversity include the tropical-temperate regions around Australia, the tropical East Pacific, and the cold-temperate water of the North Pacific (California to Alaska). Asterias is a common genus found in European waters and on the eastern coast of the United States; Pisaster, along with Dermasterias ("leather star"), are usually found on the western coast. Habitats could range from tropical coral reefs, kelp forests to deep-sea floor, although none of them live within the water column; all species of starfish found are living as benthos. Echinoderms need a delicate internal balance in their body; no starfish are found in freshwater environments.

2007-09-27 21:23:27 補充：
http://en.wikipedia.org/wiki/Starfish