We investigated the morphology and composition of the peritrophic membrane in the shrimp, Sicyonia ingentis . The peritrophic membrane is not a biological bilipid layer, but a thin sheet that lines the midgut tract of the shrimp and separates the ingested food from the epithelial layer. The peritrophic membrane persists and forms the wrapper in the fecal pellet. Although its purpose is unknown, we suggest it may act as a potential barrier to shrimp pathogens. Can bacteria and viruses ingested with food, pass through the peritrophic membrane, thereby gaining access to the epithelial and perhaps deeper tissues of the body? Rebecca is studying the structure of the peritrophic membrane using light and electron microscopy. Erin is working to determine the chemical composition of the structure. Rebecca examined the peritrophic membrane using light as well as scanning and transmission electron microscopy and was able to correlate stages in the secretion of the peritrophic membrane. Midgut tracts both with and without fully formed membranes were examined. Transmission electron microscopy allowed us to view changes in the secretory granules that are thought to form the peritrophic membrane. Erin has isolated the protein fraction from the membranes. These samples are then run on SDS gels to determine the number of proteins present and their molecular weights. The non-protein fraction is assumed to contain proteoglycans and chitin. The concentration of these materials will be compared to published results on insects. Ideally, Rebecca's histochemical staining of the intact tissue and Erin's chemical approach will claim the same materials are present in the peritrophic membrane of this crustacean, the first crustacean to be analyzed in this fashion.