echinodermata, hemichordata, chordata

echinodermata, hemichordata, chordata - Introduction...

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Introduction: Members of the Phylum Echinodermata live primarily on the ocean floor. They have adult bodies that are symmetrical at multiple points and are divided into five parts (usually called tube feet). They have an endoskeleton underneath a tender skin and have a water vascular system that is described in more detail later in the discussion. Echinoderms employ external, sexual reproduction, where the sperm and eggs are dispersed in clouds into the water in hopes that they will mix and fertilize away from the parents. Many species also have the ability to regenerate lost body parts, sometimes even dropping a body part off as a defensive or diversionary tactic. There are five classes in this phylum: Astroidea, Ophiuroidea, Crinoidea, Echiniodea, and Holothuroidea. The Class Asteroidea contains the sea stars, or starfish, that we are so familiar with. They have a oral surface (on the bottom) where the mouth is with an aboral surface on top where the anus is located. Also on the aboral surface is the Madreporite, which is critical in the function of the water vascular system. They also have dermal gills for respiration and pedicellariae for cleaning and protection. These are the most typical echinoderms, with a central body and five tube feet extending outward that have suckers on the bottom. The Class Ophiuroidea, the brittle stars, are similarly shaped but lack suckers on the bottom of their feet. Instead, these feet are used, rather poorly, for locomotion and feeding. The Class Crinoidea, consisting of Sea Lilies and Feather Stars, are thought to be rather ancient with both the mouth and the anus on the aboral side. Sea urchins and sand dollars, members of the Class Echinoidea, have five
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echinodermata, hemichordata, chordata - Introduction...

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