The regularly arranged openings acting as additional oscula – suboscula – in the skeletal structures of numerous hexactinellids made the basis for recognizing a transient level in those sponge organization: a transition between the unitary and the colonial forms. Unitary, autonomous and colonial sublevels have been recognized in the transition structures. The morphological diversity of the Late Cretaceous transitions was called forth by manifestations of mosaic morphogenesis in the representatives of the Lychniscosa and Hexactinosa orders.
