Article: The microstructure of stromatoporoids
Colin W. Stearn
Fourteen microstructures are recognized in stromatoporoid tissue, but not all are features of the tissue laid down by the organism and much fibrous, transversely porous, flocculent, pseudotubular, and melano-spheric tissue has developed from other microstructures during the process of preservation. Irregular specks of opaque matter less than 5 ft across are present in the tissue of most stromatoporoids but some have uniformly coloured tissue. During preservation these specks have moved, diffusing out into the galleries and concentrating into spheres. Fibrosity caused by intercrystalline boundaries and by the alignment of the specks transverse to the structural elements or in a water jet pattern is both an original microstructure and developed during preservation. Compact tissue in which the specks are evenly distributed passes through stages of alteration due to the concretionary tendency of the specks, in which it is successively flocculent, pseudotubular, and finally characterized by dark spherules (melanospheres).Tissue of the family Stromatoporidae is marked by subspherical voids or dark spherules. Originally the tissue was cellular, filled with subspherical voids. The tissue marked by dark spherules is here called melanospheric tissue and has been altered by the breakdown of the walls between the cellules and the concentration of the dark specks in the regions between. A puzzling feature is the occurrence of other microstructures such as micro-laminae, tubules, tripartite laminae, etc., in both black-on-white and white-on-black states interchangeably.The microstructures of 22 common genera and of the family Labechiidae are reviewed and emended diagnoses of genera provided. Clathrodictyon cannot be defined in terms of cysts placed side to side, as the holotype has regular continuous laminae. The laminae of Stictostroma and Stromatoporella contain a single line of cellules opening to the galleries on either side by a pore. Clathrocoilona has compact tissue and is closely allied to Stictostroma. Actinodictyon and Pseudoactinodictyon have compact tissue and are similar to Clathrodictyon and Anostylostroma respectively. Trupetostroma has vacuolate tissue but the vacuoles are not concentrated at the peripheries of the pillars. The median light zone of its laminae is probably the result of the merging of a plane of cellules during preservation. Most species of Idiostroma should be assigned to other genera as they have in common little but external form and do not have the microstructure of the type species. Hermatostroma is polyphyletic and includes species with compact and cellular tissue. It is characterized by marginally cellular or vesicular pillars. The tissue of Stachyodes contains fine dark or light rods. Parallelopora may be distinguished from other members of the family Stromatoporidae by its large cellules arranged in vertical series. The cysts of the Labechiidae are a single thin layer of compact tissue and the enclosing layers of flocculent or striated tissue are due to diffusion of specks into the galleries during preservation.