Meeting Abstract
Sea stars, echinoderms of the class Asteroidea, are found in all ocean basins from the intertidal to the abyssal zones. Members of this class are radially symmetric as adults and contain an endoskeleton composed of small calcium carbonate spines called ossicles.This endoskeleton supports diverse morphologies among this group, with ossicle shape varying from spines to plates. Although the ossicle structure has been compared using 2D x-rays, little work has been done to compare their organization in three dimensional space. We took high resolution micro-CT scans of nine species of stars that live around the San Juan Islands in Washington, USA. We modified a fractal analysis technique called box counting for application to 3D data to measure the complexity of the ossicle structure. The scans revealed a huge diversity in the composition of the ossicles, which varied in shape, size and arrangement. Three dimensional fractal analysis indicated highly complex organization of ossicles across all sea star endoskeletons. Using a fractal number scale of 0 to 4, 4 being the most complex, the stars included in this study ranged from 3.3 to 3.5. Ossicles may provide a range of functions for each species, including specialized prey capture, defense against predation, or habitat requirements. Future study could determine how differences in ossicle arrangement are related to the niches these species occupy.
