GENERAL CHARACTERISTICS OF ECHINODERMATA

Gr., echinos=hedgehog (it's an animal); derma=skin

They are exclusively marine, but a very few freshwater form also exist.
They may be free-living or sessile. A few are pelagic and some creeps at the bottom of the sea.
Adults possesses radial body symmetry, but the body of larval forms are bilaterally symmetrical.
Triploblastic animals i.e., body derived from 3 germ layer (ectoderm, mesoderm and endoderm).
Body is unsegmented.
Organ-system grade of body organization.
Coelom is found and is modified to form ambulacral system.
Locomotion takes place by specialized tube feet.
Radial symmetry in adult is pentamerous type i.e, each and every organs are arranged in 5 or multiples of 5.
Head and brain are absent.
Water-vascular system is of coelomic origin.
Body is differentiated into oral and aboral surface. Oral surface has an ambulacral and inter-ambulacral region.
Blood is without respiratory pigments.
Mesodermal exoskeleton is used in the form of spine.
Respiration takes place by gills, papillae or cloacal respiratory trees or by tube feet.
Circulatory system is ill developed.
Incomplete digestive system is found in some forms.
Excretory system is absent.
Nervous system consists of a circum-oral ring and many radial nerves.
Poorly developed sense organ includes pigments eyes, statocysts and tactile tentacles.
Asexual or sexual reproduction occur. Asexual reproduction by transverse fission.
Development is indirect through various larval stages.
Fertilization is external.
Dioecious animals.