Phylum Echinodermata have about 6 thousand species and have spiny skin. Marine sea stars, sea urchins, sea cucumbers, feather stars, sea lilies, and sand dollars are examples of echinoderms.
They have calcium rich endoskeleton that forms spines and plates. Echinoderms appear radially symmetrical as adults but larva is bilateral.
They have a water vascular system. Starfishes are found along the coastlines and in the ocean. Starfishes feed on clams, oysters and much more. Their mouth is underside and their aboral also known as their anus is on the top.
Pincerlike pedicellariae keep surface free of particles. Starfishes have tiny skin gills that respire and each of their arms has a groove lined by tube feet that help them open a clam. Central ventral stomach is everted into bivalve and begins external digestion.
Their nervous system has a central ring with radial nerves in each arm. Water enters their water vascular system through their sleve plate, passes through each arm and to the ampulla about each tube foot, providing slow hydraulic system or movement.
Echinoderms lack excretory, respiratory and circulatory systems. Reproduction involves asexual fragmentation, regeneration, and sexual release of eggs or sperm to reproduce bilateral larvae that metamorphose into adults.
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