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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 ...
A stalked crinoid (white) and a comatulid (red) in deep sea, showing the differences between these two sister groups. Most modern crinoids, i.e., the feather stars, are free-moving and lack a stem as adults. Examples of fossil crinoids that have been interpreted as free-swimming include Marsupites, Saccocoma and Uintacrinus. [23]
A study on the morphology of arms of fossil and modern crinoids spanning from the Ordovician to the recent, evaluating whether known crinoid clades had more capacity to evolve morphological variation around the time of their origin than later in their evolutionary history, is published by Pimiento et al. (2018). [7]
Cenometra bella is a species of crinoids belonging to the genus Cenometra.They can have up to 30 arms [2] and can be of variable colours but are often characterised by a marked contrast between the extending free-arms and the feathery pinnules (for example, dark brown and white). [2]
This waving action flings the particles away from the crinoid's mouth, keeping it clean. [9] Along the ocean floor, E. parrae is often preyed upon by pencil urchins such as Calocidaris micans. [2] The stomachs of C. mican collected around E. parrae contained large amounts of crinoid stems and soft
The earliest crinoid may have been Echmatocrinus, the fossilised remains of which have been found in the Burgess Shale, but some authorities do not accept it as a crinoid. Bourgueticrinids first appeared in the fossil record during the Triassic period, although other crinoid groups, now extinct, originated in the Ordovician .
Like extant crinoids, Agaricocrinus americanus was anchored to a hard surface by a holdfast out of which grew an articulated stalk. On top of this was a calyx with a number of feather-like arms. Each arm bore short branches known as pinnules and from these cirri were extended which sifted plankton from the water flowing past.
Platyceratidae is an extinct family of Paleozoic sea snails, marine gastropod mollusks.This family may belong in the Patellogastropoda or the Neritimorpha. [2]Platyceratids are known for the complex symbiotic relationships they had with crinoids. [3]