DEVELOPMENTAL PATTERNS OF THE HYDROSPIRES IN BLASTOIDS

This project measured the surface area of the hydrospires, or the respiratory structures, in blastoids. The hydrospires are internal canals separated into a number of thin, corrugated folds though which oxygen would diffuse. Blastoids are common Paleozoic stalked echinoderms that are often used as a model for function in brachiole-bearing blastozoans. Nearly all blastozoans have some type of respiratory structure often in the form of thin porous internal canals through which seawater is circulated for gas exchange The samples for this project were gathered from Upper Mississippian, Chersterian Age rock. The species under study are Pentremites godoni from Floraville, Saint Claire County, IL and Pentremites pyroformis from Sulphur, Crawford County, IN. The surface area of the hydrospires was calculated by taking and photographing multiple cross sections through each individual blastoid. The lengths of the hydrospire folds were measured using NIH Image, and by multiplying this by the known thickness of each section, the total surface area could be calculated. By studying the shape and surface area of the hydrospires in individuals at different stages of ontogeny, the developmental pattern of the hydrospires was established. This information was used to determine how changing metabolic requirements are compensated for in blastoids. Of particular interest is the comparison between the two species of blastoid with very different morphotypes. Also of interest are the early stages of hydrospire development. In the early post-larval stages, it appears as though little hydrospire surface area is required and that oxygen may have simply diffused through the body wall. The only modern analogs to blastoids are stalked crinoids that are generally found in deep water and respire through podia in the feeding arms. Consequently, little comparison can be made between the respiration of modern crinoids and blastoids. However, internal respiratory canals, such as the hydrospires, were common among many groups of Paleozoic, stalked echinoderms, including Parablastoids, Glyptocystitoids, Hemicosmitids, “rhomb-bearing” Crinoids. By studying the development and functional requirements of the hydrospires in blastoids, we can gain a greater understanding of the respiratory systems of many other blastozoan.