Brachiopod: Difference between revisions
Content deleted Content added
No edit summary Tag: blanking |
←Blanked the page |
||
| Line 1: | Line 1: | ||
{{AnimalsCleanup}} |
|||
{{refimprove|date=January 2007}} |
|||
{{Taxobox |
|||
| name = Brachiopoda |
|||
| fossil_range = {{fossilrange|542|0|[[Cambrian]] - Recent}} |
|||
| image = PlatystrophiaOrdovician.jpg |
|||
| image_width = 250px |
|||
| image_caption = ''[[Platystrophia]] ponderosa'' ([[Ordovician]]). Scale bar is 5.0 mm. |
|||
| domain = [[Eukarya]] |
|||
| regnum = [[Animal]]ia |
|||
| phylum = '''Brachiopoda''' |
|||
| phylum_authority = [[André Marie Constant Duméril|Duméril]], 1806 |
|||
| subdivision_ranks = [[Subphylum|Subphyla]] and [[class (biology)|class]]es |
|||
| subdivision = See [[Brachiopod#Classification|Classification]] |
|||
| diversity_link = List of brachiopod genera |
|||
| diversity = About 4,000 [[genus|genera]] |
|||
}} |
|||
'''Brachiopods''' (from [[Latin]] ''brachium'', arm + New Latin ''-poda'', foot) are a small [[Phylum (biology)|phylum]] of [[benthic]] [[invertebrate]]s. Also known as '''lamp shells''' (or '''lampshells'''), "'''brachs'''" or '''Brachiopoda''', they are [[Sessility (zoology)|sessile]], two-valved, [[Marine (ocean)|marine]] [[animal]]s with an external [[morphology (biology)|morphology]] superficially resembling [[Bivalvia|bivalve]]s to which they are not closely related. It is estimated by [[paleobiology|paleobiologist]]s that 99 percent of all documented brachiopod species are both [[fossil]]s and [[extinct]].<ref> See, for instance, data provided by [[paleontologist]] W. H. Easton (1960) in ''[[Invertebrate paleontology|Invertebrate Paleontology]]'' (New York: Harper and Brothers). </ref> |
|||
<!-- Some of this probably should be moved further down into the below sections --> |
|||
Despite superficial similarities, bivalves and brachiopods differ markedly: [[Bivalve]]s usually have a plane of symmetry between the valves of the shell, which are mirror images of each other; most brachiopods have a plane of [[symmetry (biology)#Bilateral symmetry|bilateral symmetry]] ''through'' the valves and perpendicular to the [[hinge]]. The two brachiopod valves differ in shape and size from one another. Bivalves use [[adductor muscle]]s to hold their two valves closed, and they open them by means of an external or internal [[ligament]] once the adductor muscles are relaxed. Brachiopods use internal [[diductor]] muscles to pull their two valves apart; they close the two with adductor muscles. |
|||
A second major difference is that most brachiopods are attached to the [[Substrate (marine biology)|substrate]] by means of a fleshy "stalk" or [[pedicle]]. In contrast, although some bivalves ([[pelecypod]]s such as [[oyster]]s, [[mussel]]s and the extinct [[rudist]]s) are fixed to the substrate, ''most'' are free-moving, usually by means of a muscular "foot". |
|||
Furthermore, brachiopod shells may be made of either Calcium [[Phosphate]] or — much more commonly — [[Calcium Carbonate]] (CaCO<sub>3</sub>), as mollusks generally are.[1] Lastly, in contrast to most bivalves, some extinct brachiopods exhibit elaborate [[flange]]s and [[spine]]s. |
|||
On [[July 16]], [[1986]], the Kentucky State Legislature designated the brachiopod to be the official [[Kentucky]] [[state fossil]]. |
|||
==General description== |
|||
[[Image:Lingula anatina 2.jpg|thumb|right|''[[Lingula anatina]]'']] |
|||
Brachiopods may be divided into two types: ''inarticulate brachiopods'' are held together entirely by musculature, whereas ''articulate brachiopods'' have a hinge-like articulation between the shells. All brachiopods are marine and are found either attached to substrates by a structure called a [[pedicle]] or resting on muddy bottoms. Brachiopods are suspension feeders with a distinctive feeding organ called a [[lophophore]], which is found in two other animal phyla: [[Bryozoa]] and [[Phoronida]]. |
|||
Modern brachiopods range in shell size from less than 5 mm (¼ in) to just over 8 cm (3 in). Fossil brachiopods generally fall within this size range, but some adult species have a shell of less than 1 mm across, and a few gigantic forms have been found measuring up to 38.5 cm (about 15 in) in width. |
|||
===Valves=== |
|||
Brachiopods are bi-valved, although not generally considered bivalves, a term reserved for dual valved (shelled) molluscs, pelecypods. Brachiopod valves are upper and lower rather than left and right and are designated respectively the pedical valve and brachial valve. The pedical valve is attached to the pedical and has the adjustor muscles for positioning. The brachial valve houses the brachidia, supports for the lophophore. Brachiopods, like ammonites, are often illustrated, especially in the professonal literature, upside down with the pedical valve shown ventral and the brachial valve shown dorsal; not true in nature. (MLF p 203–204) |
|||
===Articulate Shell Structure === |
|||
Articulate brachiopod shells are composed of calcium carbonate. There is an outer laminar layer and an inner fibrous layer (MLF p 204) that slopes toward the laminar layer in the direction of the shell margin. The fibrous layer contains openings known as pallial sinuses, which in life contain mantal material. In fossil forms the pattern of pallial sinuses is diagnositic in dertermining different genera. |
|||
Articulate shells are either impunctate, punctate, or pseudopunctate. Impuctate shells are solid, except for pallial openings in the fibrous layer. Punctate shells are perforated by tubules or pores, known puncti (sing. punctum) that extend from the inner side of the fibrous layer, almost to the outer side of the laminar layer. Pseudopunctate shells have rod-loke bodies of structureless calcite in the fibrous layer that may weather more readily, leaving openings that may be confused for puncti. (MLF p 203–204 ) |
|||
==Evolutionary history== |
|||
[[Image:Onniella.jpg|thumb|left|Brachiopod fossils are often found in dense assemblages, such as these specimens of the [[Ordovician]] species ''Dalmanella meeki''.]] |
|||
[[Image:Brachiopoda-morphology.png|thumb|300px|right|Brachiopod morphology]] |
|||
[[Image:Brachiopod Neospirifer.jpg|thumb|A [[Carboniferous]] brachiopod ''Neospirifer condor'', from Bolivia. The specimen is 7 cm across.]] |
|||
[[Image:Rhynchotremadentatum.jpg|thumb|''Rhynchotrema dentatum'', a rhynchonellid brachiopod from the Cincinnatian (Upper [[Ordovician]]) of southeastern Indiana.]] |
|||
[[Image:HederellaOH3.jpg|thumb|left|A [[Devonian]] spiriferid brachiopod from Ohio that served as a host substrate for a colony of [[hederellid]]s. The specimen is 5 cm wide.]] |
|||
[[Image:Syringothyris01.JPG|thumb|left|''Syringothyris'' sp.; a spiriferid brachiopod from the Logan Formation (Lower [[Carboniferous]]) of [[Wooster, Ohio]] (internal molds).]] |
|||
[[Image:PetrocraniaOrdovician.jpg|thumb|left|''Petrocrania'' brachiopods attached to a strophomenid brachiopod; Upper Ordovician of southeastern Indiana.]] |
|||
The earliest unequivocal brachiopods in the [[fossil record]] occur in the early [[Cambrian]], with the hingeless, inarticulate forms appearing first, followed soon thereafter by the hinged, articulate forms. Possible brachiopods have also been found in much older upper [[Neoproterozoic]] strata, although their assignment remains uncertain. Brachiopods are extremely common fossils throughout the [[Paleozoic]]. The major shift came with the [[Permian-Triassic extinction event|Permian extinction]]. Before this [[extinction event]], brachiopods were more numerous and diverse than bivalve mollusks. Afterwards, in the [[Mesozoic]], their diversity and numbers were drastically reduced and they were largely replaced by bivalve mollusks. Mollusks continue to dominate today, and the remaining orders of brachiopods survive largely in fringe environments. |
|||
The origin of the brachiopods is unclear; two hypotheses suggest how a bivalved lifestyle could have emerged. |
|||
{{main|Evolutionary history of brachiopods}} |
|||
The most abundant modern brachiopods are the Class [[Terebratulida]]. The perceived resemblance of terebratulid shells to ancient oil lamps gave the brachiopods their common name "lamp shell". The phylum most closely related to Brachiopoda is probably the small phylum [[Phoronida]] (known as "horseshoe worms"). Along with the [[Bryozoa]] and possibly the [[Entoprocta]], these phyla constitute the informal superphylum [[lophophorate|Lophophorata]]. |
|||
The inarticulate brachiopod genus ''Lingula'' is the oldest, relatively unchanged animal known. The oldest lingulid fossils are found in Lower Cambrian rocks dating to roughly 550 million years ago. The origin of brachiopods is unknown. A possible ancestor is a sort of ancient "armored slug" known as ''[[Halkieria]]'' that had small brachiopod-like shields on its head and tail. |
|||
During the [[Ordovician]] and [[Silurian]] periods, brachiopods became adapted to life in most marine environments and became particularly numerous in shallow water habitats, in some cases forming whole banks in much the same way as bivalves (such as [[mussel]]s) do today. In some places, large sections of [[limestone]] [[Stratum|strata]] and reef deposits are composed largely of their shells. |
|||
Throughout their long geological history, the brachiopods have gone through several major proliferations and diversifications, and have also suffered from major [[extinction]]s as well. |
|||
It has been suggested that the slow decline of the brachiopods over the last 100 million years or so is a direct result of (1) the rise in diversity of filter feeding bivalves, which have ousted the brachiopods from their former habitats; (2) the increasing disturbance of sediments by roving deposit feeders (including many burrowing bivalves); and/or (3) the increased intensity and variety of shell-crushing predation. However, it should be noted that the greatest successes for the bivalves have been in habitats that have never been adopted by the brachiopods, such as burrowing. |
|||
The abundance, diversity, and rapid evolution of brachiopods during the Paleozoic make them useful as [[index fossil]]s when correlating strata across large areas. |
|||
==References== |
|||
*{{cite book|last=Williams|first=A|coauthors=Carlson, S.J., and Brunton, C.H.C.|year=2000|chapter=Brachiopod classification|volume=2|editor=Williams, A. et al. |title=Brachiopoda (revised)|}} Part H of {{cite book|title=Treatise on Invertebrate Paleontology|editor=Kaesler, R.L.| location=Boulder, Colorado and Lawrence, Kansas|publisher=Geological Society of America and The University of Kansas |id=ISBN 0-8137-3108-9}} |
|||
*MLF (Moore, Lalicker and Fischer); Invertebrate Fossils, McGraw-Hill Book, 1952 |
|||
* [1] http://www.scienceforums.net/forum/showthread.php?p=339638 |
|||
==External links== |
|||
{{commonscat|Brachiopoda}} |
|||
*[http://www.ucmp.berkeley.edu/brachiopoda/brachiopoda.html UC-Berkeley Museum of Paleontology] |
|||
* [http://www.palaeos.com/Invertebrates/Lophotrochozoa/Brachiopoda/E0A0E0Brachiopoda.htm Palaeos Brachiopoda] |
|||
*[http://paleopolis.rediris.es/BrachNet/ BrachNet] |
|||
*[http://www.kgs.ku.edu/Extension/fossils/brachiopod.html Information from the Kansas Geological Survey] |
|||
*[http://perso.wanadoo.fr/jean-ours.filippi/brach/anglais/poursavoirplusang22.html site of R.Filippi] |
|||
*[http://paleopolis.rediris.es/Brachiopoda_Phoronida_databases/ Brachiopoda World Database] |
|||
==See also== |
|||
*[[List of brachiopod genera]] |
|||
==Footnotes== |
|||
<references/> |
|||
{{Animalia}} |
|||
[[Category:Brachiopods| ]] |
|||
[[ca:Braquiòpode]] |
|||
[[cs:Ramenonožci]] |
|||
[[de:Armfüßer]] |
|||
[[et:Käsijalgsed]] |
|||
[[es:Brachiopoda]] |
|||
[[fa:بازوپایان]] |
|||
[[fr:Brachiopoda]] |
|||
[[ko:완족동물]] |
|||
[[hr:Ramenonošci]] |
|||
[[it:Brachiopoda]] |
|||
[[ka:მხარფეხიანები]] |
|||
[[hu:Pörgekarúak]] |
|||
[[nl:Armpotigen]] |
|||
[[ja:腕足動物]] |
|||
[[no:Armføttinger]] |
|||
[[nn:Armfotingar]] |
|||
[[oc:Brachiopoda]] |
|||
[[pl:Ramienionogi]] |
|||
[[pt:Brachiopoda]] |
|||
[[ru:Плеченогие]] |
|||
[[sk:Ramenonožce]] |
|||
[[sr:Шкољке светиљке]] |
|||
[[fi:Lonkerojalkaiset]] |
|||
[[sv:Armfotingar]] |
|||
[[th:แบรคิโอพอด]] |
|||
[[tr:Dallı bacaklılar]] |
|||
[[zh:腕足动物门]] |
|||