Evolution and systematics

Nonarticulate lampshells, also known as inarticulated bra-chiopods, have been known since the Lower Cambrian period, about 550-600 million years ago. The traditional placement of these animals is in the class Inarticulata, but a more recent classification divides them into two subphyla: the Linguliformea and the Craniiformea. The living representatives of the Linguliformea are divided into two families: the Lingulidae with two genera, Lingula and Glottidia; and the Discinidae with four extant genera, Discina, Discinisca, Dis-cradisca, and Pelagodiscus. The Craniiformea have one family, the Craniidae, with four genera: Craniscus, Neoancistrocrania, Neocrania, and Valdiviathyris. The inarticulated brachiopods are related to the Phoronida (horseshoe worms).

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