HYDRODYNAMIC MODELING OF RESPIRATORY SYSTEMS IN BLASTOIDS (ECHINODERMATA)

Virtual Paleontology studies fossils through digital visualization of the three dimensional morphology. The raw data for 3D reconstructions usually involve tomographs, a series of two-dimensional parallel slices, of a specimen that are gathered either by destructive and non-destructive methodologies. Internal structures of blastoids, such as the hydrospires and other elements of the respiratory system, historically have been characterized by serial sections. Reconstructing blastoids with Photoshop, Illustrator and Rhinoceros 3D modeling software, allows for the segmentation of Regions of interest (ROI) and 3D visualization, but also gives significant flexibility for file exportation and computational synthesis. The 3D models were used as input to produce models of seawater flow through the respiratory system, which is a prerequisite to understanding their respiratory efficiency. We have constructed 3D models of the respiratory system including the incurrent hydrospire pores, hydrospires, and spiracles for Monoschizoblastus, Ellipticoblastus, Deltoblastus, Cryptoblastus and Pentremites. Seawater enters the system through a large number of small diameter hydrospire pores located at the margins of the ambulacra. Seawater then flows into a system of one or more narrowly spaced, thin walled hydrospire folds, hypothesized to be site of gas exchange. Hydrospire folds each terminate in canals, which coalesce orally into spiracles. Water flow is horizontal from the pores into the fold with an ~10X drop in velocity. Flow remains largely horizontal in the fold turning vertical in the hydrospire tube. Velocity in the tube is approximately equal to that in the fold aborally. Velocity increases rapidly adorally such that water exits the spiracle at ~ 20X the velocity seen in the hydrospire fold. External constrictions of the spiracle increase the velocity and turbulence of excurrent water from the hydrospires. These results support the hypothesis that gas exchange occurs in the hydrospire folds with the hydrospire tube acting largely as a conduit for oxygen depleted water. Blastoid genera have different hydrospire configurations with different numbers of hydrospire pores, folds and spiracles producing dynamic morphological characters that should be informative in developing blastoid phylogenies.