ACETATE PEELS AND SYNCHROTRON IMAGING REVEAL THE INTERNAL ANATOMY OF BLASTOIDS (ECHINODERMATA)

Blastoids are the longest-lived and most diverse members of the Blastozoa (Echinodermata), a major component of Paleozoic marine ecosystems. We have been studying the internal anatomy of blastoids by digitizing the acetate peels of serially sectioned blastoids from the Naturalis Biodiversity Center (NCB), Netherlands and specimens imaged at the SLS synchrotron, Paul Scherrer Institute, Switzerland. The digitized acetate peels were registered, clipped from the background and stacked in Photoshop to virtually recreate the blastoid that had been destroyed during serial sectioning. The digital images were then lofted in Rhino to produce 3D models. We used Spiers to segment synchrotron images to produce 3D models of the internal anatomy. Finally we used a laser scanner to produce external 3D models of species that had serially sectioned. Visualizations are both electronic and physical models produced via 3D printing. Our initial results have documented elements of the blastoid reproductive system including the gonopore, gonoduct and gonad in Deltoblastus and Pentremites. We have also imaged elements of the respiratory systems including hydrospires, which either are internal organs (in spiraculate grade blastoids) or externally exposed (in fissiculate grade blastoids). The 3D reconstructions allow us to not only image the hydrospires, but also begin to conduct fluid flow simulations through the modeled organs. A single specimen imaged at the SLS has about 75% of the digestive system preserved including the gut and an enlarged mid-gut region. Elements of the water vascular system including ring canal and radial water vessels can be recognized both in peels and in synchrotron data. The data are critical in understanding the autecology of the blastoids and may provide additional characters for phylogenetic reconstructions.