| Brachiopoda Fossil range: Cambrian - Recent | |
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 Platystrophia ponderosa (Ordovician). Scale bar is 5.0 mm. | |
| Scientific classification
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Kingdom |
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Phylum |
Brachiopoda |
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classes |
See Classification
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Brachiopods (from Latin brachium, arm + poda, foot) is a Phylum of marine invertebrates, also known as lamp shells (or lampshells), with an external morphology superficially resembling molluscan bivalves, known as pelecypods, although not closely related. Nearly all documented brachiopod species are extinct fossils.
Despite superficial similarities, pelecypods) and brachiopods differ markedly, both in their respective shell symmetry and internal morphology. The valves (shells) of brachiopods are bilaterally symmetrical with left and right halves but are unequal one to the other. In contrast the shells (valves) of Pelecypods Bivalvia are mirror images of each other but are not bilaterally symmetrical. Brachiopods use internal diductor muscles to pull their two valves apart and adductor muscles to close the two. Bivalves use adductor muscles to hold their two valves closed, and open them by means of an external or internal ligament once the adductor muscles are relaxed.
A second major difference is that most brachiopods are attached to the substrate by means of a fleshy "stalk" or pedicle. In contrast, most molluscan bivalves are mobile, typically by means of a muscular "foot".
Furthermore, brachiopod shells may be made of either Calcium Phosphate or — much more commonly — Calcium Carbonate (CaCO3), as mollusks generally are. Lastly, in contrast to most pelecypod bivalves, some extinct brachiopods exhibit elaborate flanges and spines.
On July 16, 1986, the Kentucky State Legislature designated the brachiopod to be the official Kentucky state fossil.
Classification[]
The Phylum Brachiopoda is now divided into three distinct subphyla, Linguliformea, Craniiformea, and Rhynchonelliformea. The Linguliformea and Craniiformea are lumped in the Inarticulata in Invertebrate Fossils, McGraw-Hill, 1952. The Rhynchonelliformea are the Articulata, ibd.Among its included orders are the Orthida, Pentamerida, Rhynchonellida, Spiriferida, Strophomenida, and Terebratulida.
Articulate brachiopods, the Rhynchonelliformea, have a pair of articulated valves (i.e. shells) with a hinge. Inarticulate brachiopods, Linguliformea and Craniiformea, have shells that are not joined or hinged, but are held together only by muscle.
Taxonomic composition[]
The Rhynconeliformea subdivided into two broad classes, the Rhynchonellata and Strophomenata. Rhynchonellata contains the orders Athyridida, Atrypida, Orthida, Pentamerida, Rhynchonellida, Spiriferida, and Terebratulida. The Strophomenata contains the Billingsellida, Orthotetida, Productida, and Strophomenida
Among the inarticulates, the Craniformea contains a single class, the Craniata, with the orders Craniida, Craniposida, and Trimerilida. Within the Lingulata are the orders Acrotretida, Lingulida, and Siphonotretida.
References[]
- Williams, A., S.J. Carlson & C.H.C. 2000, Brachiopoda (Revised). Treatise on Invertebrate Paleontology, Part H.
- MLF (Moore, Lalicker and Fischer); Invertebrate Fossils, McGraw-Hill Book, 1952