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Sexual Dimorphism

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Little Sexual Dimorphism other than gonad color; valves of females that brood are sometimes shaped to accommodate the brood pouch.
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Fairbairn DJ (2013) Odd couples: extraordinary differences between the sexes in the animal kingdom. Princeton: Princeton University Press. http://www.worldcat.org/oclc/820118780
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Articulata (Brachiopoda)

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The Articulata is a class of brachiopods which comprises those with hinged, calcareous shells that generally bear well developed teeth and sockets and a simple muscle system. The name was first applied to this major group of brachiopods by Huxley in 1869, ten years prior to Zittel choosing the same name in 1879 for modern crinoids.

The Articulata has been replaced by the subphylum Rhynchonelliformea which except for taxonomic rank and revision of some taxa within, is essentially synonymous.

Moore, Lalicker, and Fischer, 1952, divided the Articulata into the following groups:

The earlier version of the Treatise, part H, 1965, is similar, except for the elimination of the Paleotremata and the order in which the remaining orders are presented.

See also

References


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Articulata (Brachiopoda): Brief Summary

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The Articulata is a class of brachiopods which comprises those with hinged, calcareous shells that generally bear well developed teeth and sockets and a simple muscle system. The name was first applied to this major group of brachiopods by Huxley in 1869, ten years prior to Zittel choosing the same name in 1879 for modern crinoids.

The Articulata has been replaced by the subphylum Rhynchonelliformea which except for taxonomic rank and revision of some taxa within, is essentially synonymous.

Moore, Lalicker, and Fischer, 1952, divided the Articulata into the following groups:

Paleotremata Orthida Terebratulida Pentamerida Rhynchonellida Strophomenida Spiriferida

The earlier version of the Treatise, part H, 1965, is similar, except for the elimination of the Paleotremata and the order in which the remaining orders are presented.

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Articulata (Crinoidea)

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Articulata are the only extant subclass of the class Crinoidea. The group includes "sea lilies" and "feather stars". The Articulata are differentiated from the extinct subclasses by their lack of an anal plate in the adult stage and the presence of an entoneural system. Articulata exhibit pentamerous symmetry. The stalk, which consists of numerous disks held together by ligaments, supports a calyx or cup made of circlets of calcerous plates. In Comatulids, the stalk develops following the larval stage, but the juveniles shed all but the topmost disk to take up a free-living existence. Five often branched arms, which consist of articulated series of ossicles, extend from the oral plate and form the food-capture mechanism of Articulata. The arms of Articulata are pinnulate in that they have alternating pinnules branching out along them to effectively increase the surface area for feeding. These pinnules all have ciliated ambulacral grooves that converge to form larger grooves in the arms that lead down to the mouth located beside the anus on the upper surface of the oral plate.Articulata are passive suspension feeders. They capture algae with triplets of tube feet located on the pinnules, and the ciliated ambulacral canals transport this algae to the mouth. Although they are passive feeders, some Articulata have been observed to move to better feeding areas either with locomotory mechanisms at the base of the stalk or by detaching and pulling themselves with their arms. Currently there are 540 described species of Articulata that fall into two major orders. The bourgueticrinids which have the traditional stalked body form account for about 15% percent of the known species while the comatulids are unstalked and account for most of the rest.

Classification

The Articulata are subdivided into the following orders and families:[1][2]

Evolution

Articulata first appeared in the fossil record during the Triassic period although other, now extinct crinoid groups, originated in the Ordovician.

References

  1. ^ Ruppert, Edward E.; Fox, Richard, S.; Barnes, Robert D. (2004). Invertebrate Zoology, 7th edition. Cengage Learning. p. 924. ISBN 81-315-0104-3..mw-parser-output cite.citation{font-style:inherit}.mw-parser-output q{quotes:"""""'"'"}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-limited a,.mw-parser-output .cs1-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{font-size:100%}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}
  2. ^ Messing, Charles (2012). "Articulata". World Register of Marine Species. Retrieved 2013-02-11.
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Articulata (Crinoidea): Brief Summary

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Articulata are the only extant subclass of the class Crinoidea. The group includes "sea lilies" and "feather stars". The Articulata are differentiated from the extinct subclasses by their lack of an anal plate in the adult stage and the presence of an entoneural system. Articulata exhibit pentamerous symmetry. The stalk, which consists of numerous disks held together by ligaments, supports a calyx or cup made of circlets of calcerous plates. In Comatulids, the stalk develops following the larval stage, but the juveniles shed all but the topmost disk to take up a free-living existence. Five often branched arms, which consist of articulated series of ossicles, extend from the oral plate and form the food-capture mechanism of Articulata. The arms of Articulata are pinnulate in that they have alternating pinnules branching out along them to effectively increase the surface area for feeding. These pinnules all have ciliated ambulacral grooves that converge to form larger grooves in the arms that lead down to the mouth located beside the anus on the upper surface of the oral plate.Articulata are passive suspension feeders. They capture algae with triplets of tube feet located on the pinnules, and the ciliated ambulacral canals transport this algae to the mouth. Although they are passive feeders, some Articulata have been observed to move to better feeding areas either with locomotory mechanisms at the base of the stalk or by detaching and pulling themselves with their arms. Currently there are 540 described species of Articulata that fall into two major orders. The bourgueticrinids which have the traditional stalked body form account for about 15% percent of the known species while the comatulids are unstalked and account for most of the rest.

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Description

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Cup composed of radial and basal ossicles without anal plates in the adult. Infrabasals present in many fossil taxa; reduced or absent in extant taxa. Mouth exposed on the surface. Axial nerves enclosed in a canal penetrating the basals, radials, and brachials. Brachials generally joined by muscular articulation, but non-muscular (ligamentary) articulations are present in almost all species. Arms bearing pinnules in all extant taxa.
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Messing, Charles, C.G.