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Pentacrinites is an extinct genus of crinoids that lived from the Hettangian to the Bathonian of Asia, Europe, North America, and New Zealand.Their stems are pentagonal to star-shaped in cross-section and are the most commonly preserved parts. [1]
Crinoid fossils from the Jurassic showing ossicles. Several types of small ossicles are found in the body wall of sea cucumbers. Baskets are cup-shaped and usually have four projections. Buttons are disc-shaped and pierced by four holes and may be smooth or knobbed.
The numerous calcareous plates make up the bulk of the crinoid, with only a small percentage of soft tissue. These ossicles fossilise well and there are beds of limestone dating from the Lower Carboniferous around Clitheroe, England, formed almost exclusively from a diverse fauna of crinoid fossils. [15] Stalked crinoid drawn by Ernst Haeckel
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 ...
Articulated crinoid fossils are relatively rare, but disarticulated columnals are quite common in the fossil record. They may be extracted from their matrix (often limestone) or, in the case of exposures in coastal cliffs, they can sometimes be found washed out of the matrix and deposited on the foreshore, as if from the sea.
Flexible fossils are very rare in the Ordovician (the most common taxa being Cupulocrinus and Protaxocrinus), but the Late Ordovician appears to have been an interval of rapid diversification for the group. [3] Major traits of Flexibilia include: [1] [4] Three infrabasal plates (in contrast to the five found in other dicyclic crinoids).
The gonads at least periodically occupy much of the body cavities of sea urchins [47] and sea cucumbers, while the less voluminous crinoids, brittle stars and starfish have two gonads in each arm. While the ancestors of modern echinoderms are believed to have had one genital aperture, many organisms have multiple gonopores through which eggs or ...
This genus is known in the fossil record from the Devonian period to the Permian period (age range: 360.7 to 290.1 million years ago). [3] Fossils of species within this genus have been found in Australia, China, Europe and United States.