Relationship and internal structure of a new Pilina (Monoplacophora) from the late Ordovician of Oklahoma

Pilina cheyennica n. sp. (Monoplacophora) is described from the late Ordovician Keel Member of the Chimneyhill Limestone of Oklahoma and compared with other North American monoplacophorans. The species represents the first positive record of the genus from the Ordovician and from North America. Muscle scars and other internal structures are well preserved in the holotype. After a pelagic larval stage, P. cheyennica was probably a relatively mobile, benthonic
browser or deposit feeder in shallow water, unlike present day deep water monoplacophorans.