Figure 1. Comparison of the body plans of the principal lineages of living brachiopods. Mouth (m) and anus (a) are marked. (After Nielsen, 1995.) (Not to scale)

Figure 2. The principal organs of a generalized rhynchonelliform brachiopod. (After Williams and Rowell, 1965.)

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 minimze recirculation of filtered water. This animal's shell is about 40 mm across. (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 c. 10 m. The largest shell is c. 10 mm wide. There are no setae. (Photo credit: Peter Wirtz.)

Figure 5. A group of the thecideidine, articulate brachiopod Pajaudina atlantica on the roof of a small cave, La Palma, Canary Islands, depth c. 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 c. 5 mm wide. As in Megathiris, there are no setae. (Photo credit: Peter Wirtz.)

Figure 6. Time ranges of principal brachiopod lineages. (Modified from Williams A, Carlson SJ, Brunton CHC, Holmer L and Popov L (1996) A supra-ordinal classification of Brachiopoda. Philosophical Transactions of the Royal Society, B 351: 1171–1193). Lineages surviving to the present day are coloured yellow. The background curve gives an impression of changing family-level diversity through geological time. (After Rudwick, 1970.)

Figure 7. Phylogeny of brachiopods and phoronids, summarizing recent gene sequence evidence and showing the distribution of key characters mentioned in the text. The uncertain placement of the thecideidine lineage within rhynchonelliforms is indicated by a dashed line.