Comatulida
| Comatulida Temporal range:
| |
|---|---|
| |
| Lamprometra palmata | |
Scientific classification
| |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Echinodermata |
| Class: | Crinoidea |
| Subclass: | Articulata |
| Order: | Comatulida |
Comatulidais anorderofcrinoids.Members of this order are known asfeather starsand 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.
Taxonomy
[edit]Bourgueticrinida,thesea lilies,has traditionally been viewed as an order ofArticulataand a sistertaxonto Comatulida. A study published in 2011 suggested that it should be renamed Bourgueticrinina and viewed as a suborder of Comatulida.[1]
Characteristics
[edit]
Like other echinoderms, comatulids havepentameroussymmetry (five sided) as adults though the larvae havebilateral symmetry.Late in their development, the larvae are attached to the seabed by a stalk, but this is broken atmetamorphosisand 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 thesubstrateto keep the feather star in place.[2][3]
There are five long, often branched, rays attached round the edge of the tegmen. Each of these is further subdivided intobranchlets(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.[3]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. Anambulacral groovestarts 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.[3]
Behavior
[edit]
Many comatulids live in crevices, under corals or inside sponges, the only visible part being some of the arms. Some come out at night and perch themselves on eminences to feed. Many species can locomote across the seabed, raising their body on their arms. Many can also swim with their arms but most are largely sedentary, seldom moving far from their chosen place of concealment.[4]
Feeding
[edit]Comatulids aresuspension feeders.The arms are extended and held in such a position as to maximise the feeding surface with regard to the current. At each junction of the ossicles in the pinnules there are a group of three suckerlesstube feet.The longest of these searches forplanktonin the surrounding water. When a particle is found, it is gathered in and thrust into the ambulacral groove by all three tube feet. Here it is formed into a bolus with mucus and moved down to the mouth by the actions of the cilia, being retained in the groove by the lappets.[4]
Reproduction
[edit]Comatulids aredioecious,each individual being either male or female. Thegametesare produced in specialised pinnules at the base of the arms, and fertilisation is external. The larvae are planktonic and drift with the water flow. After several larval stages they settle on the seabed and anchor themselves with a stalk. At metamorphosis, the stalk breaks and the juveniles can move around.[5]
Ecology
[edit]Comatulids consist of 80%calcium carbonateand are unappetising to most predators. A number of species of fish are known to feed on them, usually pulling off a single arm or the visceral mass, both of which can be regenerated. 47% of specimens seen by one researcher were lacking one or more arms or had regenerating limbs, so sub-lethal predation is probably low. Many other invertebrates live ascommensalsamong the rays of crinoids and it may be these succulent morsels that are the principal objective of most predators.[6]The comatulidFlorometra serratissima,in the north east Pacific, has been reported as being preyed on by the gracefuldecorator crab[7]Oregonia gracilisand the sunflower seastarPycnopodia helianthoides.The loss of the arms may be due toautotomy,the shedding of an arm to save the rest of the organism. A 20 centimetres (7.9 in) arm was found to be fully regenerated in nine months in this species.[8]
Order Comatulida
[edit]The World Register of Marine Species includes the following suborders, superfamilies and families in Comatulida:[9]
- SuborderBourgueticrinina
- FamilyAtelecrinidae
- FamilyBathycrinidae
- FamilyPhrynocrinidae
- FamilyRhizocrinidae
- SuperfamilyAntedonoidea
- FamilyAntedonidae
- FamilyPentametrocrinidae
- FamilyZenometridae
- SuperfamilyComatuloidea
- FamilyComatulidae
- SuperfamilyHimerometroidea
- FamilyColobometridae
- FamilyHimerometridae
- FamilyMariametridae
- FamilyZygometridae
- SuperfamilyNotocrinoidea
- FamilyAporometridae
- FamilyNotocrinidae
- SuperfamilyTropiometroidea
- FamilyAsterometridae
- FamilyCalometridae
- FamilyCharitometridae
- FamilyPtilometridae
- FamilyThalassometridae
- FamilyTropiometridae
- Superfamilyincertae sediswithin Comatulida
- FamilyAtopocrinidae
- FamilyBourgueticrinidae
- FamilyEudiocrinidae
- FamilyGuillecrinidae
- FamilySeptocrinidae
References
[edit]- ^Hess, H; Messing, C. G. (2011) Comatulida. In: Hess H, Messing CG, Ausich WI. Treatise on Invertebrate Paleontology, Part T, Echinodermata 2 Revised, 1633 Crinoidea, vol. 3. University of Kansas Press, Lawrence, Kansas, pp. 70–146.
- ^Dorit, R. L.; Walker, W. F.; Barnes, R. D. (1991).Zoology.Saunders College Publishing. pp.790–792.ISBN0-03-030504-7.
- ^abcMessing, Charles."Crown and calyx".Charles Messing's Crinoid Pages.Archived fromthe originalon 2013-10-29.Retrieved2012-07-26.
- ^abMessing, Charles."The crinoid feeding mechanism".Charles Messing's Crinoid Pages.Archived fromthe originalon 2013-01-14.Retrieved2012-07-26.
- ^"Feather stars, Order Comatulida".Wild Singapore. October 2008.Retrieved2012-07-26.
- ^Messing, Charles."Predation on living crinoids".Charles Messing's Crinoid Pages.Archived fromthe originalon 2013-01-14.Retrieved2012-07-26.
- ^Decorator crabs are reported to snip off crinoid arms for use as camouflage.Hugh B. Cott,Adaptive Coloration in Animals,Oxford, 1940. p 360.
- ^Mladenov, Philip V. (1983). "Rate of arm regeneration and potential causes of arm loss in the feather starFlorometra serratissima(Echinodermata: Crinoidea) ".Canadian Journal of Zoology.61(12): 2873–2879.doi:10.1139/z83-375.
- ^Messing, Charles (2023)."Comatulida".WoRMS.World Register of Marine Species.Retrieved2023-12-20.