Echinoderms are usually characterized by radial symmetry, where they have several arms. The body consists of 5 equal segments in an echinoderm, where each holds different sets of internal organs. Echinoderms have no heart, brain, or eyes. Echinoderms have tentacle like structures called tube feet, they are controlled by a hydraulically vascular system. It's mouth is situated in the middle of its body on the bottom. There are about 6,000 known species of echinoderms.
Major groups
Echinoderms are marine invertebrates, with an internal skeleton and are often covered in spines.
The groups that are included in Echinoderms are:
Asteroidea (starfish) usually 5 limbs or more
Crinoidea (sea lilies, and sand dollars)
Echinoidea (sea urchins)
Holothuroidea (sea cucumbers etc.)
Ecological roles
They have ecological importance in mainly just surviving, or being eaten. Humans use echinoderms are food, medicine, and research.
Referances
http://www.starfish.ch/reef/echinoderms.html
http://www.daviddarling.info/encyclopedia/E/echinoderm.html
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