AN ASTERIGERINACEAN ORIGIN FOR ORBITOCLYPEUS AND ASTEROCYCLINA (ORBITOCLYPEIDAE, FORAMINIFERA)

A detailed structural study of the genera Orbitoclypeus and Asterocycl ina (Orbitoclypeidae) has revealed new features of the microspheric ju venarium. The initial spiral chambers of microspheric forms in both ge nera have stellar structure; that is, they have differentiated dorsal and ventral sides, the ventral one being subdivided into a main chambe rlet and a stellar chamberlet. This stellar structure indicates a phyl ogenetic relationship of the Orbitoclypeidae with asterigerinaceans, s upporting a conclusion that the Orbitoclypeidae originated from an anc estral microbenthic asterigerinacean foraminifer in the early Paleocen e. Although it needs confirmation from the study of the microspheric f orm, the genus Hexagonocyclina is considered to represent the oldest o rbitoclypeid, thus placing the origin of the family in the Caribbean B ioprovince.