Comatulida
| Comatulida | |
|---|---|
 |
|
| A feather star | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Echinodermata |
| Class: | Crinoidea |
| Subclass: | Articulata |
| Order: | Comatulida |
| Suborders | |
Bourgueticrinina
Comatulidina
Guillecrinina
Comatulida is an order of crinoids. Members of this order are known as feather stars and mostly do not have a stalk as adults. The oral surface with the mouth is facing upwards and is surrounded by five, often divided rays with feathery pinnules. Comatulids live on the seabed and on reefs in tropical and temperate waters.
Bourgueticrinida, the sea lilies, has traditionally been viewed as an order of Articulata and a sister taxon to Comatulida. A study published in 2011 suggested that it should be renamed Bourgueticrinina and viewed as a suborder of Comatulida.
Like other echinoderms, comatulids have pentamerous symmetry as adults though the larvae have bilateral symmetry. Late in their development, the larvae are attached to the seabed by a stalk, but this is broken at metamorphosis and the juvenile crinoid is free living. The body has an endoskeleton made from a number of articulated calcareous plates known as ossicles covered by a thin epidermis. It is in the shape of a cup (the calyx) with a lid (the tegmen) which has a central mouth and an anus near the edge, the gut being U-shaped. There is a ring of clawlike appendages (the cirri) near the base of the aboral underside; these grip the substrate to keep the feather star in place.
There are five long, often branched, rays attached round the edge of the tegmen. Each of these is further subdivided into branchlets (the pinnules). Most comatulids originally have 10 arms, each ray being subdivided once. The arms are fragile, and if one is broken off, at least two grow in its place; in this way the number of arms can increase. The arms are composed of articulating ossicles held together by ligaments, and the pinnules have a similar structure. The arms are very flexible and can be spread widely or coiled up. An ambulacral groove starts on each pinnule and joins with others to form grooves on the arms all leading to grooves on the tegmen ending at the mouth. These food-collecting grooves are overhung by calcareous plates (the lappets) and have a lining of fine cilia.
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Wikipedia