What they are
Brittle Starfish, Sea Cucumbers, Sea Stars ("Sand Dollars"), Crinoids, Blastoids
Morphology
All echinoderms, also called echinoids, have five-fold radial symmetry. A common example is the modern "sand dollar."
Crinoids, also known as sea lilies, and Blastoids are stalked echinoids. They have a head, or calyx, to which is attached five or more arms. These arms are used to channel food towards the mouth, located at the center of the calyx. The calyx is attached to a stalk, which is composed of numerous round plates known as columnals. The key difference between crinoids and blastoids is that the arms of a crinoid have nervous systems, while those of a blastoid do not.
Sea stars and brittle stars usually have five arms and a mouth at the center of the bottom of the animal.
Ecology
Echinoids live on the sea floor, an area known as the benthic zone. In some of the deepest waters (>1000m), sea cucumbers and brittle stars make up the vast majority of sea floor biota, sometimes as high as 90%.
There are no freshwater or terrestrial (land) echinoderms. Almost all echinoids (>99%) live strictly in areas of normal marine salinity. This means that echinoids cannot survive in waters with an above average area of dissolved salts, like lagoons and brine marshes.
Echinoids vary in tactics when obtaining food. Some echinoids attach to rocks or inside cracks and gather food particles from the over passing water. Some burrow through the mud to find bits of food. Still, other echinoids actively hunt for their prey by slowly crawling along the sea floor in search of such animals as clams, barnacles, and corals. Crinoids and blastoids get their food from gathering food particles from over passing water.