310 FOSSIL INVERTEBRATES/Bryozoans Modern Brachiopod Faunas Further Reading Despite their relative rarity today as compared with the Palaeozoic, living brachiopods are actually widespread, represented mainly by pedunculate forms attached to a variety of substrates across a spectrum of water depths At high latitudes, brachiopods range from intertidal depths to basinal environments at depths of over 6000 m They are most common in fjord settings in Canada, Norway, and Scotland and in the seas around Antarctica and New Zealand The association between the horse mussel, Modiolus modiolus, and Terebratulina retusa is particularly widespread in the Northern Hemisphere In the tropics, however, many species are micromorphic, exploiting cryptic habitats in reef crevices or in the shade of corals and sponges Larger forms live in deeper water environments, evading groups of predators that might graze on meadows of newly attached larvae Benton MJ and Harper DAT (1997) Basic Palaeontology Harlow: Addison Wesley Longman Brunton CHC, Cocks LRM, and Long SL (eds.) (2001) Brachiopods Past and Present Systematics Association Special Volume Series 63 London and New York: Taylor and Francis Carlson SJ and Sandy MR (eds.) (2001) Brachiopods Ancient and Modern A Tribute to G Arthur Cooper Paleontological Society Papers New Haven: Yale Uni versity Reprographics Clarkson ENK (1998) Invertebrate Palaeontology and Evolution, 4th edn Cambridge: Blackwell Science Harper DAT and Moran R (1997) Brachiopod life styles Geology Today 13: 235 238 Harper DAT and Rong J (2001) Palaeozoic brachiopod extinctions, survival and recovery: patterns within the rhynchonelliformeans Geological Journal 36: 317 328 Kaesler RL (ed.) (1997 2002) Treatise on Invertebrate Paleontology, Part H, Brachiopoda (revised), vol Boulder, CO and Lawrence, KS: The Geological Society of America and the University of Kansas (continuing) Nielsen C (2002) Animal Evolution: Interrelationships of the Living Phyla, 2nd edn Oxford: Oxford University Press Williams A, Carlson SJ, Brunton CHC, Holmer LE, and Popov LE (1996) A supra ordinal classification of the Brachiopoda Philosophical Transactions of the Royal Society, Biological Sciences 351: 443 481 See Also Biological Radiations and Speciation Fossil Invertebrates: Bryozoans; Bivalves Mesozoic: End Cretaceous Extinctions Palaeozoic: Cambrian; Ordovician; End Permian Extinctions Sedimentary Environments: Carbonate Shorelines and Shelves Bryozoans P D Taylor, The Natural History Museum, London, UK Copyright 2005, Natural History Museum All Rights Reserved Introduction The Bryozoa are a phylum of colonial invertebrates occasionally referred to as Ectoprocta or by the obsolete name Polyzoa Because the great majority of bryozoan species possess calcareous skeletons, they are among the commonest groups of macrofossils found in the post-Cambrian marine fossil record Bryozoans are active suspension feeders In common with most other suspension feeders, they not need to move in search of food and, with a few exceptions, are sessile, living permanently anchored to a hard surface, such as a rock, shell, or seaweed Although present-day bryozoans can be found living in freshwater lakes and slow-flowing rivers, the majority are marine, inhabiting depths from the intertidal to the abyssal Most modern species are stenohaline, and fossil bryozoans are almost exclusively marine owing to the absence of mineralized skeletons in freshwater species All bryozoans are colonial Each colony comprises a group of genetically identical modular units called zooids Zooid size enables bryozoans to be distinguished from colonial corals (see Fossil Invertebrates: Corals and Other Cnidaria), with which they are occasionally confused: bryozoan zooids seldom exceed mm in maximum surface dimension, whereas the equivalent coral structures (corallites) are typically centimetric in scale Colony growth occurs mostly by the addition of new zooids, a process termed budding, supplemented in some groups by lengthening of existing zooids Fully grown colonies of some species contain fewer than 10 zooids, whereas other species may develop colonies containing many thousands of zooids, which may on occasion reach 50 cm in diameter Anatomy and Feeding The basic bryozoan zooid consists of a body wall enclosing a fluid-filled cavity (coelom or pseudocoel)