sponges

Integrated Bio and Magnetostratigraphic Study of the ≪Ozerki≫ Sections (Upper Cretaceous, Right Bank of the Volga in the Saratov Region). Paper 2. Oryctocoenosis Characteristics and Biostratigraphy

Authors: Pervushov E. M., Seltzer V. B., Kalyakin E. A., Fomin V. A., Ryabov I. P., Ilinskiy E. I., Gujikova A. A., Biryukov A. В., Surinskiy A. M.

In the ≪Ozerki≫ sections, in the terrigenous and carbonate rocks, a faunal complex has been determined – unusually diversified and relatively abundant for the right-bank part of the Saratov Region. Examination of the specified groups of fossil invertebrates has allowed to propose variants for biostratigraphic division and correlation of the sections under consideration. The carbonate rocks are supposed to belong to the Turonian-Coniacian and the underlying terrigenouscarbonate rocks are regarded as the Lower Turonian ones.

Module Organization in the Late Cretaceous Hexactinellids (Hexactinellida, Porifera)

Authors: Pervushov E. M.

Knowledge on the regularities of vegetative propagation and comprehension of the osculum (oscula) and subosculum structural-functional positions and interrelations in the skeleton structure have made it possible to specify the organization levels in the Late Cretaceous hexactinellids: the unitary (solitary, perifrontal and autonomous forms), transitory (solitary, autonomous and colonial forms) and colonial (primary and true colonies) ones.

Morphotypes of the Late Cretaceous Hexactinellids (Porifera, Hexactinellida)

Authors: Pervushov E. M.

Basic structure types have been specified in hexacinellids with soldered spicule lattice. The fossils of those occur as skeletal forms. Certain tendencies in Lychniscosa and Hexactinosa morphogenesis were identified as conductive to shaping the spectrum of skeleton archetypes. The increase of sponge morphological diversity was in many ways predetermined by thickness reduction of the skeleton-forming walls, associated with reduction of the irrigation system elements. That has brought about forms of complicated tubular labyrinth habits.

Morphogeneses of the Late Cretaceous Guettardiscyphia (Porifera, Hexactinellida)

Authors: Pervushov E. M.

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.

Regenerative Capabilities in the Late Cretaceous Hexactinellids (Porifera, Hexactinellida)

Authors: Pervushov E. M.

Partial and complete regeneration phenomena, cases of skeleton habitus restoration have been recorded in representatives of the Late Cretaceous hexactinnelids. Regeneration incidences are in many ways associated with the ability of silicon-producing cells responsible for constructing skeleton-generating elements, spicules, to transform, to rearrange their functions in response to the changes of the organism position on the substrate surface and/or upon the changes of the aquatic environment parameters.

Unitary Late Cretaceous Hexactinellids (Porifera)

Authors: Pervushov E. M.

Hexactinellids comprise diverse types of sponges viewed as solitary ones. They used to constitute the basis of sponge communities in the Middle-Late Jurassic and Middle Cretaceous of the European region. The morphological diversity of unitary forms is determined by the skeletal structure with combination of a goblet, a shaft, a false shaft and a system of rhizoids. The goblet wall is peculiar for the highest morphological flexibility, which contributes to substantial habitus changes of the skeleton original morphotypes.

Transitory Level of Modular Organization in the Late Cretaceous Hexactinellids (Porifera)

Authors: Pervushov E. M.

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.

Colonial Level of Modular Organization in the Late Cretaceous Hexactinellids (Porifera). Genuine Colonies

Authors: Pervushov E. M.

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.

Neogenesis in Structure of Skeletons of Late Cretaceous Sponges Contributed to the Formation of Polyosculumic Forms

Authors: Pervushov E. M.

Arterial directions in formation of module organization of skeleton hexactinellids are caused by vegetative forms of reproduction. It is supposed that some tendency of selection of protozoa module forms can be traced in morphogenesis of separate generic types of late Cretaceous sponges. The concept “polyosculumic„ sponges is considered in vast context personally in reference to skeletons with some osculumics formed in the result of partial regeneration of organism

Perifrontal Forms of the Late Cretaceous Modular Hexactinellids (Porifera)

Authors: Pervushov E. M.

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

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