| The echinoderms (phylum Echinodermata) are the sea stars, sea urchins and their kins. There are 6000 species, all marine that are distinguished by a pentamerous radial symmetry. They have an endoskeleton made of calcareous ossicles and spiny ossicles on the whole body. They possess a water vascular system and body appendages, the podia, that are used in feeding locomotion and respiration. In general, the sexes are separate, the fertilization is external and the development is planktonic. Echinoderms are divided into 5 classes that are: |
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