Original Description Test is biserial throughout, with variable asymmetry as seen in edge view. Earlier species displays twisted tests and periapertural structures; evolved one shows symmetrical tests in edge view and asymmetrical periapertural structures. When compared with the second chamber, the size of the proloculus is variable and generally larger, but in some rarer specimens it is smaller. Chamber shape is globular to reniform. Sutures are distinct, depressed, straight, and oblique to the test axis of growth. Test periphery is rounded. Aperture is a low to medium high arch at the base of the last formed chamber and bordered by asymmetrical periapertural structures. Periapertural structures of the primitive species consist of a subangular ridge on one side and a rim on the opposite side; two asymmetrical flanges border the aperture in the evolved species. A small, relict toothplate can be occasionally present. Chamber surface is smooth. Test wall is calcitic, hyaline, nannoperforate to microperforate. Size: Etymology: The Greek prefix ‘‘proto-’’ (= first) is added to Heterohelix. Extra details from original publication Remarks. Protoheterohelix is the only Cretaceous heterohelicid planktic foraminiferal genus known with an asymmetrical test or periapertural structures. It includes the earliest biserial planktics and is the only genus of the family Heterohelicidae Cushman, 1927 from the upper Albian–lower Cenomanian stratigraphic interval. Asymmetry of the test and periapertural structures is a vestige of its benthic ancestry (i.e., Praeplanctonia Georgescu, 2009). All Protoheterohelix descendants display completely symmetrical tests. Species included. Protoheterohelix washitensis (Tappan), 1940; P. obscura n. sp.
Stratigraphic range. Upper Albian–lower Turonian.
Geographic distribution. USA (Texas), Gulf of Mexico, western North Atlantic Ocean (Blake Plateau) and Europe (Germany, North Sea, and Poland). Editors' Notes
Georgescu, M. D. & Huber, B. T. (2009). Early evolution of the Cretaceous serial planktic foraminifera (late Albian-Cenomanian). Journal of Foraminiferal Research. 39: 335-360. gs
Protoheterohelix compiled by the pforams@mikrotax project teamviewed: 7-12-2022