Response

You can tell that echinoderms dont have a very highly developed nervous system because they dont have heads. Some echinoderms have a nerve ring tha surrounds their mouth, and radial nerves that attached the nerve ring with the body sections. Most echinoderms also have sensory cells that are scattered on the body. These cells detect light, gravity, and chemicals released by potential prey.
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Ecology

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Echinoderms live in a marine enviroment. From the intertidal zone down to the bottom of the deep sea trenches they live in nothing but the salt water of the ocean. Some varieties live in sand and rubble, while others make coral reefs their home.  Echinoderms can live anywhere from tropical to fairly cold waters.  Starfish are echinoderms that make inhabit coral reefs or cling to rocks.  They live among fish, coral and ocean plants, and are a key role to the coral reef flourishing; they, along with brittle stars, prevent algal mats from growing.  Urchins live among the rubble and sand of the ocean floor.  Their grazing reduces the rate of colonization of bare rock.  Sand dollars and sea cucumbers encouraged deeper penetration of the sea floor, increasing the depth oxygen reaches, which allows more complex ecological layering to develop.  Some types of parasites, including crabs, worms and snails, are dependent on sea cucumbers for survival.  Echinoderms in general make up a good portion of sea animals diets, including the sea otter.