Chaetetids, the major framebuilders of Middle Carboniferous reef mounds, are poorly understood biologically. Recent recognition that chaetetids are coralline demosponges provides a sound basis for better understanding this simple poorly studied group. Improving our knowledge of these builders of reef mounds, known hydrocarbon reservoirs of the Carboniferous, has useful economic implications, as well as basic scientific value. Coralline demosponges with a chaetetid-grade skeleton are now known to be polyphyletic. Thus, it is necessary to reevaluate and revise their classification by studying calicle morphology. This study will address: (1) taphonomic (diagenetic) alteration, (2) "astogeny" (3) possible polymorphism, (4) ecophenotypic plasticity, and (5) the relationship between calicle morphology and the primary and secondary skeletons in the three basic growth forms. Other morphological features, such as the spacing and frequency of tabulae, will also be addressed. Morphometric analysis of data obtained from strained and unstained thin sections and acetate peels will be the principal method employed, combined with available detailed ecological data to determine the relative importance of the five points noted above. Integration of information obtained will aid in: (1) establishing a viable taxonomy, (2) understanding the demise of chaetetid-grade demosponges at the Westphalian-Stephanian boundary and their pantropical distribution , (3) understanding the reefal occurrences of Carboniferous chaetetid-grade demosponges, and (4) evaluating the possible relationship between chaetetids and algal symbionts.
