- Rhynchonellida
Taxobox
image_width = 240px
image_caption = "Hiscobeccus capax"
name = Rhynchonellida
regnum =Animal ia
phylum =Brachiopoda
classis =Rhynchonellata
ordo = Rhynchonellida
ordo_authority = Kuhn, 1949
subdivision_ranks = Superfamilies
subdivision =Pugnacoidea Dimerelloidea Norelloidea Hemithiridoidea Ancistrorhynchoidea †Rhynchotrematoidea †Uncinuloidea †Camarotoechioidea †Rhynchotetradoidea †Lambdarinoidea †Wellerelloidea †Rhynchoporoidea †Stenoscismatoidea † See text for genera.Thetaxonomic order Rhynchonellida is one of the two main groups of living articulatebrachiopod s, the other being the orderTerebratulida . They are recognized by their strongly ribbed wedge-shaped or nut-like shells, and the very shorthinge line.The hinges come to a point, a superficial resemblance to most (
phylogenetic ally unrelated)bivalve mollusk shells. The loss of the hinge line was an important evolutionary innovation, rhynchonellids being the first truly non-strophic shells with a purely internal articulation (teeth-sockets).Rhynchonellids lack any
brachidium , and are therefore able to extrude theirlophophore out from the shell into the water for more efficient food-gathering. It has been suggested this is why they survived theDevonian ,Permian -Triassic , andJurassic extinctions, while many otherlampshell s with a brachidium failed to do so.Strong radiating ribs are common in this group; and there are generally very strong plications or accordion-like folds on the sulcus (the long middle section) of the shell. This probably helps regulate the flow of water in and out of the shell. All rhynchonellids are biconvex (have a bulbous shell), and have a fold located in the
brachial valve . This means that thecommissure , the line between the two valves or shells, is zigzagged, a distinguishing characteristic of this group. The prominent beak of thepedicle valve usually overlaps that of the brachial valve, in order to allow the shell to open and close. There is usually a functionalpedicle although thedelthyrium may be partially closed.Morphologically, the rhynchonellid has changed little since its appearance during the
Ordovician period. It seems to have evolved frompentamerid s, and in turn gave rise to the firstatrypid s andathyrid s, both of which are characterized by the development of a complex spiral brachidium. Although much diminished by the terminal Paleozoic extinction, it experienced a revival during the Early Jurassic period, and became the most abundant of all brachiopods during theMesozoic Era.Classification
This classification down to the level of
genera is based on Kazlevcite web | author = M. Alan Kazlev | accessdate = March 10 | accessyear = 2006 | url = http://www.palaeos.com/Invertebrates/Lophotrochozoa/Brachiopoda/Rhynchonellida.htm | title = Order Rhynchonellida] and Emig [cite web | author = Christian C. Emig | title = Systematics of extant brachiopod taxa | url = http://paleopolis.rediris.es/BrachNet/CLASS/DOC/Classext.pdf | accessdate = March 10 | accessyear = 2006] .Extant subgroups
* SuperfamilyPugnacoidea
** FamilyBasiliolidae
*** SubfamilyAcanthobasiliolinae
**** "Acanthobasiliola "
*** SubfamilyBasiliolinae
**** "Basiliola "
**** "Basiliolella "
**** "Eohemithiris "
**** "Rhytirhynchia "
*** SubfamilyUncertain
**** "Striarina "
* SuperfamilyDimerelloidea
** FamilyCryptoporidae
**** "Aulites "
**** "Cryptopora "
* SuperfamilyNorelloidea
** FamilyFrieleiidae
*** SubfamilyFreileiinae
**** "Frieleia "
**** "Compsothyris "
**** "Grammetaria "
**** "Sphenarina "
*** SubfamilyHispanirhynchiinae
**** "Abyssorhynchia "
**** "Hispanirhynchia "
**** "Manithyris "
**** "Parasphenarina "
*** SubfamilyNeorhynchiinae
**** "Neorhynchia "
** FamilyTethyrhynchiidae
**** "Tethyrhynchia "
* SuperfamilyHemithiridoidea
** FamilyHemithyrididae
**** "Hemithiris "
**** "Pemphixina "
** FamilyNotosariidae
**** "Notosaria "Extinct Subgroups
* SuperfamilyAncistrorhynchoidea
* SuperfamilyRhynchotrematoidea
* SuperfamilyUncinuloidea
* SuperfamilyCamarotoechioidea
* SuperfamilyRhynchotetradoidea
* SuperfamilyLambdarinoidea
* SuperfamilyWellerelloidea
* SuperfamilyRhynchoporoidea
* SuperfamilyStenoscismatoidea References
Text taken from Kazlev with permission.
External links
* [http://www.geo.arizona.edu/geo3xx/geo308_fall2002/4brachiopds.htm Phylum Brachiopoda]
* [http://www.earth.rochester.edu/ees207/Brachiopoda/hardman_brach3.html Brachiopoda - Classification]
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