SEM ESTABLISHES A CONNECTION FOR THE FUSED SETULES OF BARNACLE LARVAL SWIMMING APPENDAGES

Due to small size and slow swimming, most zooplankton exist in a world dominated by viscous forces, Re<1, where movement results from reciprocating appendages with high and low drag postures. Crustacean zooplankton have plumose appendages consisting of setae with setules that form open fans (high drag) and semi-closed or collapsed setal arrays (low drag) during the power stroke-recovery cycle. The thoracic swimming appendages of barnacle cyprids (last larval instar) are unusual in that the setules of adjacent setae are joined at their tips to create a linkage that is an ordered mesh. How these setules are connected was explored with scanning electron microscopy (SEM). Neither light microscopy nor SEM show interlocking or hooked structures at the setule tips. SEM images show the linkages consist of two setules with slightly curved tips that adhere to one another. With SEM we found a similar linkage pattern among the appendages of four balanamorph species. Attempts to chemically disrupt these linkages were unsuccessful. Setal arrays were spread with a coverslip to break the connections and allowed to close to simulate the relaxed position of the appendages. Upon being reopened, the setular linkages were found to have re-formed. What causes the natural adhesion between setule tips is still unknown. Further exploration of adhesion and surface properties of the setules is needed. The result of this study enhances our understanding of the functional anatomy of the swimming appendages of cirriped cyprids and could apply to a similar phenomenon found in copepods, a related taxon. 

Presentation Preference: Poster

Primary Presenter: Roberto Ponce, California State University of Long Beach (poncer.8575@gmail.com)

Authors:

Roberto Ponce, California State University of Long Beach  (poncer.8575@gmail.com)

Richard Emlet, Oregon Institute of Marine Biology  (remlet@uoregon.edu)