Meeting Abstract

80.5  Sunday, Jan. 6  Analysis of the fluid flow through the complex internal respiratory structures of an extinct Paleozoic echinoderm HUYNH, TL*; EVANGELISTA, D; MARSHALL, CR; Univ. of California, Berkeley; Univ. of California, Berkeley; Univ. of California, Berkeley huynhtony@berkeley.edu

Blastoids were a group of stalked, sessile echinoderm preserved in rocks that span the middle Ordovician (~470 mya) to the end of the Permian (~250 mya). These extinct echinoderms possessed hydrospires, uniquely complex internal thecal structures with putative respiratory function. Here, we present measurement and visualization of flow within the hydrospires using a 3D-printed and Reynolds-similar physical model of the interior of a hydrospire of the blastoid Pentremites rusticus, to examine in further detail possible functions of the hydrospire. Specifically, the model allows examination of the extent to which the pattern of flow within the hydrospire kept oxygen-rich incurrent water separated from water that had already been depleted of oxygen. If the flow pattern within the hydrospire fails to keep these two bodies of water separate, this would suggest some other function for the hydrospires. In addition, the model also allows for determination of whether active pumping would have been required to achieve optimal respiratory function, or whether passive pumping alone was sufficient. Furthermore, the model allows for testing of the hypothesis that the need for removal of digestive waste, thought to be associated with the hydrospires, is responsible for some unusual aspects of the hydrospires, such as the conical shape of the putative excurrent canals and the presence of cover plates over the remarkably large excurrent openings.