Artikel: Articulata (Crinoidea) GudangMovies21 Rebahinxxi

    • Source: Articulata (Crinoidea)

      • Articulata are a subclass or superorder within the class Crinoidea, including all living crinoid species. They are commonly known as sea lilies (stalked crinoids) or feather stars (unstalked crinoids). 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 first appeared in the fossil record during the Triassic period although other, now extinct crinoid groups, originated in the Ordovician.


      Characteristics


      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. As of 2004, there are 540 described species of living 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


      According to the World Register of Marine Species, Articulata includes the following families:

      order Comatulida Clark, 1908
      super-family Antedonoidea Norman, 1865
      family Antedonidae Norman, 1865
      family Pentametrocrinidae AH Clark, 1908
      family Zenometridae AH Clark, 1909
      super-family Atelecrinoidea Bather, 1899
      family Atelecrinidae Bather, 1899
      super-family Comatuloidea Fleming, 1828
      family Comatulidae Fleming, 1828
      super-family Himerometroidea AH Clark, 1908
      family Colobometridae AH Clark, 1909
      family Eudiocrinidae AH Clark, 1907
      family Himerometridae AH Clark, 1907
      family Mariametridae AH Clark, 1909
      family Zygometridae AH Clark, 1908
      super-family Notocrinoidea Mortensen, 1918
      family Aporometridae HL Clark, 1938
      family Notocrinidae Mortensen, 1918
      super-family †Paracomatuloidea Hess, 1951
      super-family Tropiometroidea AH Clark, 1908
      family Asterometridae Gislén, 1924
      family Calometridae AH Clark, 1911
      family Charitometridae AH Clark, 1909
      family Ptilometridae AH Clark, 1914
      family Thalassometridae AH Clark, 1908
      family Tropiometridae AH Clark, 1908
      Comatulida incertae sedis
      family Atopocrinidae Messing, 2011 (in Hess & Messing, 2011)
      family Bathycrinidae Bather, 1899
      family Bourgueticrinidae Loriol, 1882
      family Guillecrinidae Mironov & Sorokina, 1998
      family Phrynocrinidae AH Clark, 1907
      family Septocrinidae Mironov, 2000
      order Cyrtocrinida
      Sub-order Cyrtocrinina
      family Sclerocrinidae Jaekel, 1918
      Sub-order Holopodina
      family Eudesicrinidae Bather, 1899
      family Holopodidae Zittel, 1879
      order †Encrinida
      family †Encrinidae
      order Hyocrinida
      family Hyocrinidae Carpenter, 1884
      order Isocrinida
      Sub-order Isocrinina
      family Cainocrinidae Simms, 1988
      family Isocrinidae Gislén, 1924
      family Isselicrinidae Klikushkin, 1977
      family Proisocrinidae Rasmussen, 1978
      Sub-order †Pentacrinitina
      family †Pentacrinitidae Gray, 1842
      order †Millericrinida


      References

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    articulata crinoidea