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 The class Echinoidea contains organisms commomly known as sea urchins, heart urchins or sand dollars.
Sea urchins are sphereical, oval, or disk shaped, and unlike other echinoderms, they have no legs. Instead, their bodies are covered with long sharp spines and pedicellariae used for defense, both which can have poisin glads.
Sea urchins feed on algae and plant life on the ocean floor and in tide pools using a structure called aristotle's lantern. This very complex structure scrapes food off the bottom of the sea floor and breaks it down, it consists of hundreds of parts including many stages of teeth. Some kinds of urchins burrow into the sand for shelter and food or even burrow into rocks using their teeth.
Sand dollars and sea bisquits do not live often in tide pools but on the ocean floor. They also have no arms, but their spines are delicate hairs used for movement. They eat by sucking sand and debris into their mouths and filtering out organic matter. Both urchins and sand dollars have tube feet on their undersides.
The urchins' tests, or their endoskeletons, are delicate and beautiful and they are collected around the world. |
