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 How are starfish, brittle stars, sea urchins, sea daisies, and sea cucumbers alike? They are all echinoderms! They are all marine animals. They all have spiny skin like a hedgehog. They all start out as swimming larvae as young and then live on the sea bottom as adults. There are over 6500 species of echinoderms that live in all the world's seas. There are 950 species of sea urchins. What does a sea urchin look like? Sea urchins usually are round and can be up to 14 inches wide. Most are about 2 to 5 inches wide. They are brown with red or yellow spots to bright red, orange, yellow, blue, or purple. |
Where can I find a sea urchin in the ocean? They can be found in many places in the world's oceans. Sea urchins can be found in tide pools to water over 15,000 feet deep. They can be found in all seas from the equator to the North and South poles.
How many groups of sea urchins live in the oceans? There are two groups of sea urchins: regular and irregular. The regular sea urchins are round with the mouth and bottom at opposite ends. The regular sea urchins have the five-star pattern like a starfish. The irregular type is flat, oval, or heart-shaped with the mouth and bottom in different places. Both types have five alternating arm zones where the tube feet can be found. They also have five interconnecting points that don't have tube feet. Sea urchins use their tube feet to move on the sea bottom or rocks. The mouth can be found on the lower part of the body on any sea urchin. A sea urchin's mouth contains a special rasping structure with teeth called "Aristotle's lantern". All sea urchins eat small plants called plankton and organic matter in the sand or mud.
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How does a sea urchin move and protect itself? The spines of a sea urchin are attached to the body with ball-and-socket joints that work like your arm. The spines can rotate in all directions allowing the sea urchin to move. The stalk-like things sticking out of the spines have pincers to remove small insects that land on the sea urchin. The spines are very sharp and some species of sea urchins have poisonous ones. The body of the sea urchin is covered with skeletal pieces that are stitched together. |
