The genus Plocezyga microgastropod biostratigraphic zonation of the Pennsylvanian of the United States

Benthic gastropods are not commonly useful for biostratigraphic zonation. The gastropod genus Plocezyga is abundant throughout the marine units of the Desmoinesian through Virgilian Pennsylvanian strata in the United States. The protoconch of Plocezyga gives evidence that it had a planktonic time within its life cycle, which would give it a wider regional distribution. It has been found that Plocezyga is able to biostratigraphically zone the Pennsylvanian of the United States by use of first-occurrence range zones. The upper Atokan stage through the Virgilian Stage can be zoned using of the first occurrences of Plocezyga conica , P. excellens , P. ampla new species, P. costata , P. subquadrata , P. ornata , P. acuminata , P. obscura , and P. procera new species. The lower and upper boundary of the Desmoinesian as well as the lower boundary of the Missourian Stage are defined by these gastropod zones. Six new species are proposed: Plocezgya ampla from upper Desmoinesian units; Gamizyga lenterotunda from Missourian units; and Plocezyga pingurestis , Plocezyga procera , Cyclozyga promohumera , and Cyclozyga diversarevolvi from Virgilian units. UUID: http://zoobank.org/d070c5ad-b65f-4ab1-842f-36058704a335