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Articulata (Crinoidea)
Encyclopedia
Articulata are the only extant subclass of the class Crinoidea. They are differentiated from the extinct subclasses by their lack of an anal plate and the presence of entoneural system. Articulata are stalked echinoderms with pentamerous symmetry. Their stalk, which consists of numerous disks held together by ligaments, supports an aboral cup made of circlets of calcerous plates. five arms, which consist of articulated series of ossicles, extend from the aboral 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 aboral 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 groups. The bourgueticrinids which have the traditional stalked body form account for about 15% percent of the known species.
period although other, now extinct crinoid groups, originated in the Ordovician
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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 groups. The bourgueticrinids which have the traditional stalked body form account for about 15% percent of the known species.
Classification
The Articulata are subdivided into the following orders and families:- Bourgueticrinida
- BathycrinidaeBathycrinidaeBathycrinidae is a family of echinoderms in the class Crinoidea. It contains the following genera and species:* Bathycrinus Wyville Thomson, 1872** Bathycrinus aldrichianus Wyville Thomson, 1877** Bathycrinus australis AH Clark, 1907...
- Bathycrinidae
- Comatulida
- AntedonidaeAntedonidaeAntedonidae is a family of crinoids or feather stars in the phylum Echinodermata. Members of the family are unstalked and have ten feathery arms...
- Atelecrinidae
- Charitometridae
- Colobometridae
- ComasteridaeComasteridaeComasteridae is a family of crinoids. Members of this family are characterized by possession of one or paired blade-like or knob-like projections on a few to many of the outer segments of the oral pinnules that together form structures called combs...
- Pentametrocrinidae
- Tropiometridae
- Antedonidae
Evolution
Articulata first appeared in the fossil record during the TriassicTriassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
period although other, now extinct crinoid groups, originated in the Ordovician
Ordovician
The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
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