Although we were both jazzed about this project, we were both also in the middle of our own dissertations, so for the next year I collected stars when I happened upon individuals of the appropriate size. By the next summer when Cassandra returned to FHL, I had collected 9 different species.
Star diversity. After scanning the stars, Cassandra used Dataviewer and Slicer 3D software to segment the scans the render the 3D images. In addition, she was able to coordinate the colors of the images to show relative density of the individual ossicles across all nine species (Figure 4). Not surprisingly, the sunflower star (Pycnopodia helianthoides) had the smallest average ossicle density relative to the other sea stars. This species is the only star of the nine scanned that relies on hydrostatic pressure rather than the organization of the ossicles to maintain its body shape, drawing extra water into itself to “puff itself up.” This greatly increases its flexibility and potentially allows it to be lighter and faster as it chases its prey. Across most of the stars scanned, the most dense ossicles were typically found in areas that could be considered the most vulnerable to the star: the ambulacral grooves, arm tips and mouth/stomach. The ambulacral grooves are the “valley” regions on the underside of the star from which the soft tube feet protrude. Each arm tip runs the risk of being the first thing to hit a potential hazard as they’re crawling along the seafloor, as well as also containing eye spots to assist in navigation. During feeding, the soft, fragile stomach is often completely everted through the mouth to digest food from outside the body, leaving the area vulnerable and attractive to predators.