Phylum Echinodermata ("Spiny Skin")
Description
There is about 7000 species in Echinodermata. All Echinoderms are marine. As adults, they are radially symmetrical, usually with five parts. Their early development is "deuterostome", which means the second opening becomes the mouth. This is more closely related to Chordates than any other animals. They have an endoskeleton made of calcium carbonate plates. They possess a water vascular system for movement, feeding, respiration and circulation. They have tube feet with Ampulla; a dilated cavity in the end of the foot. Their nervous system consists of a central nerve ring, which branches outward. They perform external fertilization with separate sexes. Species in Phylum Echinodermata are Starfish, Sand Dollars, Sea Cucumbers, Sea Slugs, Sea Stars and Sea Urchins.