Shell design inBolivinita quadrilatera, B. pohana, andB. compressa(Foraminiferida)

Abstract

Aspects of the morphology of 3 related Neogene species of Bolivinita are described and some features are related to the structural design of the shells. Possible hydromechanical consequences of the architectural differences between B. quadrilatera (rectangular spiral profile) and B. compressa (flattened, alate, spiral profile) are inferred but, qualitatively, no outstanding advantages of the descendant alate form (B. compressa) are apparent. Both taxa occupied deep water biotopes. Biometric data on spiral shape of the species (topotypic or near topotypic material) does not support previous views that B. pobana was the immediate ancestor of B. compressa. Toothplate construction in the group involves partial closure of the antecedent aperture. The location and shape of the tooth plate indicate that it would impede rather than Iaci litate the passage of cytoplasm.