Carlson, Sandra J. Department of Geology, University of California, Davis, California.
Last reviewed:December 2019
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A subphylum of inarticulated brachiopods having a bivalved calcitic shell with a laminar (tabular) secondary shell layer that is distinctly different from the microstructure of the calcareous articulated brachiopods. Together with Linguliformea and Rhynchonelliformea, Craniiformea is one of the three subphyla currently recognized in phylum Brachiopoda. It encompasses a single class Craniata, which is composed of three orders: Craniopsida, Craniida and Trimerellida. Thirty-eight genera are currently recognized within Craniiformea, with 5 genera in Craniopsida, 16 genera in Craniida and 17 genera in Trimerellida. Formerly considered to be a superfamily in order Acrotretida, Craniiformea has since been elevated to subphylum status based on the distinctive combination of a lack of tooth-and-socket hinge mechanism between the valves, the lack of a pedicle (a cuticle-covered stalklike appendage which emerges between the valves and attaches the brachiopod to the substrate) and the presence of a calcareous shell. See also: Acrotretida; Brachiopoda; Inarticulata; Lingulida; Rhynchonelliformea
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