Valve orientation and functional morphology of the foramen of some siphonotretacean and acrotretacean brachiopods

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It has recently been suggested that the foramen of siphonotretacean and acrotretacean brachiopods functioned as an exhalant siphon and that it was a feature of the dorsal valve. In representatives of these superfamilies the pedicle was considered to have emerged from between the valves. Re-examination of the evidence on which these arguments were based suggests that some of it is capable of more than one interpretation. The remainder, together with consideration of the mantle canal patterns, cemented mode of attachment, and comparative morphology of some discinaceans and siphonotretaceans, strongly supports the traditional view that the foramen of these forms was located in the ventral valve and that it served as a pedicle opening.