Articulata (Echinodermata) - Accessscience from Mcgraw-Hill Education

Articulata (Echinodermata) - AccessScience from McGraw-Hill Education http://www.accessscience.com/content/articulata-echinodermata/053200

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Article by: Fell, Howard B. Formerly, Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts. Publication year: 2014 DOI: http://dx.doi.org/10.1036/1097-8542.053200 (http://dx.doi.org/10.1036/1097-8542.053200)

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The only surviving subclass of the Crinoidea, differentiated during Triassic times. The calyx is dicyclic, but considerable reduction of the infrabasals and basals may occur. The uniserial arms bear pinnules and usually branch, and the arm retains its movable articulation with the radial plate, despite the incorporation of the lower brachial ossicles into the calyx. Extant stalked forms with nodal rings of cirri (Metacrinus) are included in the order Isocrinida (see illustration). They do not tolerate turbulant waters and live at depths below current action, although they do inhabit shallow water when the conditions are suitable. These forms may trail the stem during temporary free-swimming phases, using the cirri for reattachment. The feather stars, of the order Comatulida, discard the stem when young, and thereafter remain free, either as swimming animals or as creeping benthic forms. They prefer shallow, clear water, rich in nutrients, and therefore abound on tropical coasts and in polar seas rather than in temperate waters. Four other orders have been defined; one of them includes extinct floating forms. See also: Crinoidea (/content/crinoidea/168000); Echinodermata (/content/echinodermata/210700)

Metacrinus cyaneus, a living, articulate stalked crinoid from Bass Strait, at 200 fathoms (1200 ft or 365 m).

Howard B. Fell

1 of 3 3/15/2016 9:26 AM Articulata (Echinodermata) - AccessScience from McGraw-Hill Education http://www.accessscience.com/content/articulata-echinodermata/053200 Bibliography

A. H. Clark, Monograph of the Existing Crinoids, U.S. Nat. Mus. Bull. 82, 1915–1967

Additional Readings

M. J. Benton and D. A. T. Harper, Introduction to Paleobiology and the Fossil Record, Wiley-Blackwell, Chichester, West Sussex, UK, 2009

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