sea urchin

sea urchin
1. any echinoderm of the class Echinoidea, having a somewhat globular or discoid form, and a shell composed of many calcareous plates covered with projecting spines.
2. a tall evergreen shrub or small tree, Hakea laurina, of Australia, having narrow leaves and dense, globe-shaped clusters of crimson flowers with long yellow stamens.
[1585-95]

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Any of about 700 species (class Echinoidea) of echinoderms found worldwide.

Sea urchins have a globular body covered with movable, sometimes poisonous, spines up to 12 in. (30 cm) long. Pores along the internal skeleton accommodate slender, extensible, often sucker-tipped tube feet. Sea urchins live on the seafloor and use their tube feet or spines to move about. The mouth is on the body's underside; teeth are extruded to scrape algae and other food from rocks. Some species excavate hiding places in coral, rock, or even steel. Roe of some species is eaten in certain countries.

Slate-pencil urchin (Heterocentrotus mammillatus)

Douglas Faulkner

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 any of about 950 living species of spiny marine invertebrate animals (class Echinoidea, phylum Echinodermata) with a globular body and a radial arrangement of organs, shown by five bands of pores running from mouth to anus over the test (internal skeleton). The pores accommodate tube feet, which are slender, extensible, and often sucker-tipped. From nodules on the test arise long, movable spines and pedicellariae (pincerlike organs); these structures may have poison glands. The mouth, on the underside of the body, has a complex dental apparatus called Aristotle's lantern, which also may be venomous. The teeth of Aristotle's lantern are typically extruded to scrape algae and other food from rocks, and some urchins can excavate hiding places in coral or rock—even in steel. Sea urchins live on the ocean floor, usually on hard surfaces, and use the tube feet or spines to move about. In addition, a few carnivorous species have been described.

      The largest urchin (known from a single specimen) is Sperostoma giganteum of deep waters off Japan. Hatpin urchins, such as Centrostephanus longispinus of the Mediterranean and eastern Atlantic, Diadema (formerly Centrechinus) setosum of the Indo-Pacific, and D. antillarum of Florida and the West Indies, have toxic spines up to 30 centimetres (12 inches) long. The slate-pencil urchin (Heterocentrotus mammillatus) of the Indo-Pacific has 12-cm spines that may be 1 cm thick—stout enough to be used for writing. Lytechinus variegatus, a pale-greenish urchin of the southeastern coast of the United States and the Caribbean, and the large, short-spined Psammechinus (sometimes Echinus) miliaris of Iceland, Europe, and western Africa use their tube feet to hold up bits of seaweed or shell as a shield against sunlight in shallow water.

      The small, reddish or purplish urchins of the genus Arbacia, such as A. punctulata, the common urchin from Cape Cod to the West Indies, are familiar subjects in embryology; a female may release several million eggs at a time. In the West Indies, sea eggs—the ovaries of Tripneustes ventricosus—are eaten raw or fried; in the Mediterranean region, frutta di mare is the egg mass of Paracentrotus lividus (the best known rock borer) and other Paracentrotus species; and, on the U.S. Pacific coast, the eggs of the giant purple (or red) urchin (Strongylocentrotus franciscanus) are similarly considered a delicacy. The slightly smaller S. purpuratus, of the same region, is known to excavate holes in steel pilings. See also cake urchin; heart urchin.

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Universalium. 2010.

Look at other dictionaries:

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  • Sea urchin — Sea ur chin (Zo[ o]l.) Any one of numerous species of echinoderms of the order {Echinoidea}. Note: When living they are covered with movable spines which are often long and sharp. [1913 Webster] …   The Collaborative International Dictionary of English

  • sea urchin — sea .urchin n a small round sea animal with a hard shell covered in sharp points …   Dictionary of contemporary English

  • sea urchin — sea ,urchin noun count a small round animal that lives in the ocean and has a hard shell with sharp points …   Usage of the words and phrases in modern English

  • sea urchin — ► NOUN ▪ a marine animal which has a shell covered in mobile spines …   English terms dictionary

  • sea urchin — n. [so named because of its spines] any of various orders of echinoid echinoderms having a somewhat globular body of fused skeletal plates studded with long, calcareous, movable spines …   English World dictionary

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  • sea urchin — UK / US noun [countable] Word forms sea urchin : singular sea urchin plural sea urchins a small round animal that lives in the sea and has a hard shell with sharp points …   English dictionary

  • sea urchin — noun shallow water echinoderms having soft bodies enclosed in thin spiny globular shells • Hypernyms: ↑echinoderm • Hyponyms: ↑edible sea urchin, ↑Echinus esculentus, ↑sand dollar, ↑heart urchin • Member Holonyms: ↑ …   Useful english dictionary

  • sea urchin — sea ur·chin (seґ urґchin) any of various marine animals of the class Echinoidea, having round bodies enclosed in a shell with spiny processes and pedicellariae protruding from it. Genera such as Diadema and Echinothrix may secrete venom from… …   Medical dictionary


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