sea urchin

sea urchin

noun

Definition of SEA URCHIN

: any of numerous echinoderms (class Echinoidea) that are usually enclosed in thin brittle globular tests covered with movable spines

First Known Use of SEA URCHIN

1591

sea urchin

noun    (Concise Encyclopedia)

Slate-pencil urchin (Heterocentrotus mammillatus)—Douglas Faulkner

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.