транситорные колонии

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.

Tremabolites sponges known among the Middle-Late Cretaceous beds in Europe are reliably identifiable due to the numerous openings against the background of the skeleton smooth upper surface. The ideas of the level of organization in these sponges and of the species characteristics are far from being univocal. The paper deals with the species diversity of Tremabolites common in the Coniacian – Santonian rocks from the Volga Region. Examples of regeneration and budding in the representatives of the group are presented.