Patzkowsky, Mark E. Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania.
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An extinct order of brachiopods, in the subphylum Rhynchonelliformea, that inhabited shallow seas of the Paleozoic and early Mesozoic. It was the most diverse group of spire-bearing brachiopods (those that contain a spirally coiled calcareous structure called the brachidium, which is used to support the lophophore). Members of the order Spiriferida also possess unequally biconvex valves that are externally smooth or radially ribbed. The valves are generally strophic (straight hinge), with a well-developed interarea commonly limited to the ventral valve (illus. a–c). Shells may be punctate (possessing small perforations filled by outer epithelial tissue) or impunctate. Punctate shells arose in stratigraphically younger spiriferids; the presence or absence of punctae serves to distinguish two major taxonomic groups.
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