Crinoidea

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Related to crinoid: class Crinoidea, Sea lilies

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 ?
The participation of such cells in the regeneration of arms in crinoids and brittlestars has also been suggested (Candia Carnevali et al.
Devonian cladid crinoid evolution, diversity and first and last occurrences: summary observations.
Researchers are interested in crinoids not just because they are part of Earth's history, but because the various crinoid species were able to survive millions of years of climate changes to become the sea lilies we know today.
The most common of these are crinoids (sea lilies), snails, clam-like brachiopods, and ancestors of today's squids that had shells back then.
Different types of fauna, observed in the formation, include brachiopods, bryozoans, crinoids, bivalves and foraminifera (fusulinids).
Siderite within the Barnsdall Formation of northeastern Oklahoma occurs in four varieties: (1) large nodules lacking a distinct central nucleus, concentrated in horizons bearing articulated crinoids; (2) small concretions with distinct skeletal nuclei consisting of infaunal bivalves and inarticulate brachiopods occurring in horizons relatively lacking in articulated crinoids and crinoid material; (3) large sideritized burrows occurring above crinoid horizons; and (4) concretions nucleated around former sites of soft tissue in large crinoids and productid brachiopods.
Gahn and Baumiller examined more than 2,500 crinoid fossils for evidence of arm regeneration, focusing on specimens dating back 290 million to 490 million years.
We dig through shale and limestone filled with crinoid fragments and brachiopods, the fossilized skeletons of creatures who inhabited Brown's Ridge five hundred million years ago, when we all would have been standing at the bottom of a shallow salty sea.