Ultrastructure, morphology, affinities and reclassification of Cassigerinella Pokorný (Foraminiferida: Globigerinina)

Abstract. Re-examination of Cassigerinella chipolensis (Cushman & Ponton) and comparison of the ultrastructure of its morphotypes demonstrates that the species should only contain forms with a smooth surface and that those with a pore-cone surface should be distinguished as the type species, C. boudecensis Pokorný, a name which is still valid both taxonomically and stratigraphically. Strong resemblance in surface structure, aperture pattern and essential biseriality between many heterohelicids and Cassigerinella has been considered to be significant for its reclassification. Cassigerinella is, therefore, believed to have originated among the Heterohelicacea rather than in the Globigerinacea or Hantkeninacea as previously proposed by various authors. Morphological features, such as apertural modifications and coiling mode, and the characteristics of several related taxa of the species-group are discussed.