субоскулюм

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.

Guettardiscyphia skeletons are peculiar for thin walls and highly dense apo- and prosopores. Wall mobility was conductive to formation of conical lobate skeletons of various, occasionally geometrically regular outlines. Substantial number of fossil samples from variously composed rocks from all the Upper Cretaceous intervals has made it possible to trace skeleton transformations in sponge ontogenesis and depending on their environmental conditions.