Brachiopoda

Abstract

Brachiopods are predominantly sessile, filter‐feeding marine invertebrates, with a ciliated, tentaculate feeding and respiratory organ called the lophophore. Their body is enclosed in a shell consisting of two unequal valves oriented dorsally and ventrally. Brachiopods appeared first in the Lower Cambrian and were dominant members of Palaeozoic benthic communities until the Permo–Triassic mass extinctions. Today represented by approximately 110 genera, brachiopods are considered a minor phylum; they live in all oceans, from the poles to the tropics, in a broad depth range from intertidal to abyssal. Brachiopods make up the two main clades: the articulate rhynchonelliforms with calcitic valves joined by a mineralised hinge, and the inarticulate linguliforms and craniiforms, whose valves are joined only by soft tissues. Articulated forms give the phylum its common name: ‘lamp shells’. In some recent molecular analyses, inarticulate brachiopods and phoronids form a single clade.

Key Concepts:

  • Brachiopods are sessile, filter‐feeding marine invertebrates with a bivalved shell and are quite distinct from bivalve molluscs.

  • Brachiopods first appeared in the Lower Cambrian and were dominant members of Palaeozoic benthic communities until the Permo–Triassic mass extinctions.

  • Brachiopods are considered to be a relict group but live in all oceans and in a broad depth range.

  • Brachiopods are divided into two main groups according to the presence or absence of a mineralised tooth‐and‐socket hinge between the two valves.

  • A lophophore in the form of two arms lined with ciliated tentacles serves as a feeding and respiratory organ.

  • Based on some molecular analyses, phoronids may belong within Brachiopoda, forming a single clade with inarticulate brachiopods.

Keywords: Brachiopoda; lophophore; inarticulate brachiopod; articulate brachiopod; Phoronida

Figure 1.

Comparison of the body plans of the principal lineages of living brachiopods. Mouth (m) and anus (a) are marked. After Nielsen, (Not to scale).

Figure 2.

The principal organs of a generalised rhynchonelliform brachiopod. After Williams and Rowell, . © Geological Society of America.

Figure 3.

Close‐up view of the rhynchonelliform, articulate brachiopod Liothyrella neozelanica in feeding position with its gape fully open, showing a conspicuous fringe of marginal setae and the curtain‐like lophophore forming inhalant and exhalant compartments within the mantle cavity. The inhalant current enters at the sides and the exhalant current leaves centrally. In many fossil and extant deep‐water forms, the inhalant and exhalant currents are offset by a median fold or groove in the shell, presumably to minimise recirculation of filtered water. This animal's shell is approximately 40 mm across. Reproduced from a photograph provided by L. Shackleton, Wellington, New Zealand.

Figure 4.

A group of the rhynchonelliform, articulate brachiopod Megathiris detruncata on the wall of a small cave, south coast of Madeira, depth 10 m. The largest shell is approximately 10 mm wide. There are no setae. Photo credit of Peter Wirtz.

Figure 5.

A group of the thecideide, articulate brachiopod Pajaudina atlantica on the roof of a small cave, La Palma, Canary Islands, depth approximately 15 m. The complexly folded lophophore is supported by bas‐relief ridges on the brachial valve and the shell gapes very widely. Each shell is approximately 5 mm wide. As in Megathiris, there are no setae. Photo credit of Peter Wirtz.

Figure 6.

Time ranges of principal brachiopod lineages. Modified from Williams et al.. © Royal Society. Lineages surviving till the present day are coloured yellow. The background curve gives an impression of changing family level diversity through geological time. After Rudwick, .

Figure 7.

Phylogeny of brachiopods and phoronids, summarising recent gene sequence evidence and showing the distribution of key characters mentioned in the text. The uncertain placement of the thecideide lineage within rhynchonelliforms is indicated by a dashed line.

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References

Cohen BL (2000) Monophyly of brachiopods and phoronids: reconciliation of molecular evidence with Linnaean classification (the subphylum Phoroniformea nov.). Proceedings of the Royal Society, London, Series B 267: 225–231.

Cohen BL (2013) Rerooting the rDNA gene tree reveals phoronids to be ‘brachiopods without shells’; dangers of wide taxon samples in metazoan phylogenetics (Phoronida; Brachiopoda). Zoological Journal of the Linnean Society 167: 82–92.

Nielsen C (1995) Animal Evolution: Interrelationships of the Living Phyla. Oxford: Oxford University Press.

Rudwick MJS (1970) Living and Fossil Brachiopods. London: Hutchinson.

Sandy MR (2010) Brachiopods from ancient hydrocarbon seeps and hydrothermal vents. In: Kiel S (ed.) Topics in Geobiology: The Vent and Seep Biota, Vol. 33, pp. 279–314. London, New York, Dordrecht Heidelberg: Springer‐Verlag GmbH.

Williams A, Carlson SJ, Brunton CHC, Holmer L and Popov L (1996) A supra‐ordinal classification of the Brachiopoda. Philosophical Transactions of the Royal Society B 351: 1171–1193.

Williams A and Rowell AJ (1965) Brachiopod anatomy. In: Moore RC (ed.) Treatise on Invertebrate Paleontology, Part H, Brachiopoda, pp. 6–57. Boulder, CO and Lawrence, KA: Geological Society of America and University of Kansas Press.

Further Reading

Carlson SJ and Sandy MR (eds.) (2001) Brachiopods ancient and modern. A tribute to G. Arthur Cooper. Paleontological Society Papers 7: 1–261.

Cohen BL, Gawthrop AB and Cavalier‐Smith T (1998) Molecular phylogeny of brachiopods and phoronids based on nuclear‐encoded small subunit ribosomal RNA gene sequences. Philosophical Transactions of the Royal Society, B 353: 2039–2061.

Cohen BL, Stark S, Gawthrop AB, Burke ME and Thayer CW (1998) Comparison of articulate brachiopod nuclear and mitochondrial gene trees leads to a clade‐based redefinition of protostomes (Protostomozoa) and deuterostomes (Deuterostomozoa). Proceedings of the Royal Society, London, Series B 265: 475–482.

Cohen BL and Weydmann A (2005) Molecular evidence that phoronids are a subtaxon of brachiopods (Brachiopoda: Phoronata) and that genetic divergence of metazoan phyla began long before the Early Cambrian. Organisms, Diversity and Evolution 5: 253–273.

Hyman LH (1959) The Invertebrates: Smaller Coelomate Groups. London: McGraw‐Hill.

Kaesler R (ed.) (1997–2006) Treatise on Invertebrate Paleontology, Part H, Brachiopoda (revised), vol. 1–5. Boulder, CO and Lawrence, KA: Geological Society of America and University of Kansas Press.

Richardson JL (1986) Brachiopods. Scientific American 255: 96–102.

Selden PA (ed.) (2007) Treatise on Invertebrate Paleontology, Part H, Brachiopoda (revised), vol. 6. Boulder, CO and Lawrence, KA: Geological Society of America and University of Kansas Press.

Willmer P (1990) Invertebrate Relationships. Cambridge: Cambridge University Press.

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How to Cite close
Bitner, Maria Aleksandra, and Cohen, Bernard L(Apr 2013) Brachiopoda. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001614.pub3]