Meeting Abstract

115.1  Tuesday, Jan. 7 10:15  Holistic Morphometrics of Sand Dollar Echinoids Using Geographic Information Systems Technology ZACHOS, L G; University of Mississippi lgzachos@olemiss.edu

A mature individual of the Northern Sand Dollar Echinarachnius parma has a skeleton composed of approximately 1000 individual calcite plates. There are significant changes in number, size, orientation, and location of plates throughout ontogeny. There is also significant variation within populations of these echinoids, although it has been difficult to quantify. The flattened, relatively 2-dimensional architecture of a sand dollar offers a unique opportunity to test the use of Geographic Information Systems (GIS) technology for morphometric studies. All of the plates of individual specimens are manually digitized from scaled photographs and converted into topologically correct polygons. These polygons are labeled by plate type and indexed using an echinoid-centric numbering system. This permits the determination of plate cohorts and allows not only static measure of plate location and dimension, but also the ability to map the changes in size and relative position during growth. Such information is proving invaluable for development of computer models of growth in these organisms. Although the data are originally collected in a 2-D reference frame, GIS software facilitates overlay of upper and lower surfaces for visualization of vertical plate juxtaposition. With the addition of 3-dimensional information, obtained either by direct measurement or optical means, fully 3-D models can be created. GIS software functionality includes scaling, transformation, annotation, data conversion, and spatial analysis. Using GIS, it is possible to study plate development using every element of the echinoid skeleton, quantify individual plate growth, measure plate translocations, and correlate growth dependencies between oral and aboral plates.