Back Echinoidea AF قنفذ البحر Arabic قنفذ البحر ARZ Equinoidea AST Dəniz kirpiləri AZ دنیز کیرپیلری AZB Tayom BCL Марскія вожыкі BE Марскія вожыкі BE-X-OLD Морски таралежи Bulgarian
| Sea urchin | |
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| Class: | Echinoidea
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Sea urchins are spiky members of the class Echinoidea of the phylum Echinodermata. Like the rest of the echinoderms, they are entirely marine. They are globe-shaped, and protected by calcareous plates and spines.
Urchin is an old word for hedgehog, and in many foreign languages these animals are called sea hedgehogs.
Like other echinoderms they have five-fold symmetry (called pentamerism) and move by means of hundreds of tiny, transparent, adhesive 'tube feet'. The symmetry is not obvious in the living animal, but is easily visible in the dried test.
Sea urchins mostly feed on algae and small animals. They have a special chewing apparatus called Aristotle's lantern, after the Greek philosopher Aristotle who was fascinated by sea urchins. With this apparatus they can scrape organisms stuck to the surface over which the urchin is moving.