modular organization

In the structure of modular organization of the Late Cretaceous hexactinellid sponges, the terminal position is assigned to colonial forms, with skeletons peculiar for complex, intricate structures. Primitive (primary) and genuine (secondary) colonies have been revealed. Skeletons of the primary forms, generally with multiple numbers of equivalent modules and oscula, differ morphologically from the genuine colonies in undeveloped module connecting elements, such as junctions and wall closures, and in the lack of ostia

In morphogenesis of the Late Cretaceous skeletal sponges – hexactinellids – certain tendencies may be traced that allow to distinguish forms of diverse levels of modular organization (?polyoscula? sponges) among the unitary representatives of the group. Skeletons of the sponges from the primary level of modular forms, autonomies, represent an example of the initial module polymerization, with the principal polymerization mechanism involving diverse variants of gemmation and/or fission

Certain tendencies are supposed to show up in morphogenesis of the Late Cretaceous skeletal sponges, hexactinellids; those tendencies make it possible to distinguish some forms of diverse-level modular organization among the unitary representatives of the group. Generation of primitive ?modular? forms, defined as the perifrontal ones, is associated with incomplete gemmation and isolation of solitary cross canals, apo- or prosochetes

Tendencies of morphogenesis in the Late Cretaceous modular forms contributed to formations of complexly structured secondary (genuine) colonies. Skeletons of genuine colonial sponges differ not just in numerous and diversely arranged equivalent oscula-carrying modules, but in the presence of the module connecting elements – junctions, as well. Characteristic elements of genuine colony skeletons – ostia – have been recognized between the modules and the junctions.

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.