The term "echinoderm" means spiny skinned and is a very appropriate name for invertebrates in this group. Sand dollars, sea cucumbers, sea stars (sometimes called starfish) and sea urchins are all echinoderms. There are an estimated 70,000 species that belong to this group and echinoderms are only found in the marine environment. Unique to the bodies of all echinoderms is the water-vascular system. This hydraulic system -- a water-filled ring with canals radiating from it -- is used to provide the echinoderms with movement. Each canal is connected to many tube feet, each of which has the ability to grab onto an object through the use of suction. Working together, the tube feet can move the animal along, or can move food towards the animal’s mouth.
Types
Invertebrates
Arthropods are invertebrates with an exoskeleton, a hard and protective outer shell made of chitin. They also have appendages that are jointed and their bodies are segmented.
Cnidarians are invertebrates with stinging cells called nematocysts. Included in the cnidarian group are anemones, corals, and jellyfish.
There are an estimated 50,000 species that belong to the invertebrate group known as Mollusca. Members of this diverse group have soft bodies which are composed of a head region and a foot region.
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