Crinoidea


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Crinoidea:

see EchinodermataEchinodermata
[Gr.,=spiny skin], phylum of exclusively marine bottom-dwelling invertebrates having external skeletons of calcareous plates just beneath the skin. The plates may be solidly fused together, as in sea urchins, loosely articulated to facilitate movement, as in sea
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; feather starfeather star,
common name of a class of echinoderms that, as juveniles, are attached to the sea bottom by a stalk with rootlike branches; the mouth side faces upward. In the adult stage they break away from the stalk and move about freely.
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; sea lilysea lily,
stalked echinoderm of the class Crinoidea. Sea lilies are ancient, having reached their peak in the Middle Mississippian period; about 5,000 fossil species are known. About 80 modern species remain.
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Crinoidea

 

a class of benthic invertebrates of the phylum Echinodermata. They have a cup-shaped body, or calyx, in the middle of which is a mouth; the body is crowned by feathery, generally branching, upwardly directed rays. There are five rays at the base of the calyx and ten or more (up to 200) further up. The loose crown forms a net for catching small planktonic organisms and detritus, upon which the crinoids feed.

Stalked crinoids, or sea lilies, have a segmented stalk, which is up to 1 m long. Fixed to the base of the calyx, the stalk attaches itself to the sea bottom. Stalkless crinoids, or comatulids, have numerous movable processes (cirri) and can crawl and swim. Sea lilies, of which there are approximately 80 species, are found at depths to 9,700 m. Stalkless forms, of which there are about 550 species, are most diverse in the shallow waters of tropical seas and are often brightly colored. Adult invertebrates develop from free-swimming larvae and a sessile stalked stage.

More than 5,000 species of fossil crinoids have been traced to the Lower Ordovician. They reached the height of their development in the Middle Paleozoic (several subclasses). By the end of the Paleozoic, most species had become extinct. The subclass Articulata, to which all extant crinoids belong, has been traced back to the Triassic.

REFERENCES

Zhizn’ zhivotnykh, vol. 2. Moscow, 1968.
Hyman, L. H. The Invertebrates, vol. 4. New York-London, 1955.

Crinoidea

[krə′nȯid·ē·ə]
(invertebrate zoology)
A class of radially symmetrical crinozoans in which the adult body is flower-shaped and is either carried on an anchored stem or is free-living.
References in periodicals archive ?
A natural history of the Crinoidea or lily-shaped animals, with observations on the genera Asteria, Euryale, Comatula, and Marsupites.