Ankumia van Veen, 1932 (nomen dubium): pathological moult retention in the Cytherellidae (Platycopida: Ostracoda)

Abstract

The monotypic genus Ankumia is associated with the rich cytherellid fauna described by van Veen (1932) from the Upper Cretaceous (late Maastrichtian) rocks of South Limburg. The Netherlands. The type species (A. bosqueti van Veen, 1932) is redescribed because the genus possesses the enigmatic combination of cytherellid (posterior sex-dimorphism and R/L overlap) and eridostracan (several concentric bands) characters. As no holotype was designated, the redescription is based on a detailed SEM examination of the syntypes in the Bonnema/van Veen composite collection. Most syntypes show that the outer layer of coarse, concentric, rings, which form an oblique cone, are retained moults of a species of cytherellid. The point of retention in the early instars is along the posteroventral margin, contrary to the dorsal position of successive lamellae in eridostracan Cryptophyllus. Other syntypes possess the typical lateral outline of adult species of Cytherellidae. The ontogeny of each individual of retained moults ('Ankumia') has a nine-instar pattern, with a growth increment between successive moults about 1.15, slightly less than that (about 1.20) observed by Shaver (1953) for Cytherella bullata. The name Ankumia is abandonned, and a new combination proposed for the previous type species. Platella bosqueti (van Veen, 1932). Show more