sea urchin

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Any of various echinoderms of the class Echinoidea, having a soft body enclosed in a round, symmetrical, calcareous shell covered with long spines.

Century Dictionary and Cyclopedia

1. n. An echinoid; any member of the Echinoidea; a sea-egg or seahedgehog. Many of the leading forms have popular designations or vernacular book-names, as heart-urchins, Spatangidæ; helmet-urchins, Galeritidæ; shield-urchins, Scutellidæ; turban-urchins, Cidaridæ. The common green sea-urchin of New England is Strongylocentrotus drobachiensis (figured under the generic word). A purple sea-urchin is Arbacia punctulata. Toxopneustes franciscorum is a Californian sea-urchin used for food by Indians, and the common European one figured under Echinus is classic in the annals of gastronomy. The species here figured is flatter and less prickly than usual; still flatter ones are those known as cake-urchins, sand-dollars, etc. (See sanddollar.) Some sea-urchins have spines several inches long, and in others the spines become heavy clubs. Sea-urchins, like sea-anemones, are common objects on most sea-coasts, and their dry tests, usually lacking the spines, are often of beautiful tints. See Echinus, also cuts under ambulacrum, Ananchytes, cake-urchin. Cidaris, Clypeastridæ, Echinoidea, Echinometra, Echinothuriidæ, Echinus, Encope, lantern, petalosllchous, and Strongylocentrotus.

Wiktionary

1. n. Any of many marine echinoderms, of the class Echinoidea, commonly found in shallow water, having a complex chewing structure named Aristotle's lantern

GNU Webster's 1913

1. (Zoöl.) Any one of numerous species of echinoderms of the order Echinoidea.

WordNet 3.0

1. n. shallow-water echinoderms having soft bodies enclosed in thin spiny globular shells