The “proloculus” of the giant fusulinid Eopolydiexodina darvasica (Dutkevich) (Schwagerinoidea) from the Kubergandian (= Roadian = early Middle Permian) of Afghanistan is, in fact, an embryonic apparatus of the excentrilepidinoid-type, which has a small internal protoconch that is completely surrounded by a wide deuteroconch. The protoconch is exceptionally well preserved, but this type of apparatus is probably present in other fusulinids including other species of Eopolydiexodina, such as E. megasphaerica (Leven), and some neoschwagerinids such as Lepidolina multiseptata (Deprat). Within the Fusulinoidea, Quasifusulina seems to be the first representative of this trend, beginning in the Late Pennsylvanian/Early Permian.
This embryonic apparatus is a supplementary character of “larger foraminifera”, linking the fusulinids to such classical, more recent groups as Orbitopsellidae, Orbitoididae and Discocyclinidae. Other characteristics shared with the larger foraminifera are complexity of endoskeleton, endosymbiotic algae and trimorphism. The existence of trimorphism among the fusulinids is postulated but poorly studied. Dimorphism (or trimorphism?) has been present since the Early Permian in Robustoschwagerina, Anderssonites, Rugofusulina and Ruzhenzevites, and perhaps Alpinoschwagerina (formerly Pseudoschwagerina) and Zellia. Among the foraminifera, the schwagerinoids are probably the first group in which the trimorphic reproduction cycle became common; this group may also have been the first which lived in endosymbiosis with algae. The dimorphism or trimorphism is especially conspicuous in the advanced schwagerinoids Parafusulina, Skinnerina, Eopolydiexodina and Polydiexodina. The life cycle of Eopolydiexodina is reconstructed to include cycles of gamonts, agamonts and schizonts, and the embryonic apparatus-bearing forms may correspond to the gamont A2 generation.