Insights on the morphological aspects of lipid accumulation and excretion in adult Caryophyllaeus brachycollis (Cestoda, Caryophyllidea)

Abstract This is the first ultrastructural study of an adult tapeworm providing data on the morphological aspects of the pathways of lipid excretion via the tegumental surface and excretory system in the monozoic tapeworm Caryophyllaeus brachycollis (Janiszewska, 1953) from the chub Squalius tenellus (Heckel, 1843) obtained from a lake in the Bosnia-Herzegovina Federation. Our study has shown that the release of lipid droplets onto the parasite–host interface from the tegumental cytoplasm is carried out with the participation of tegumental vesicles, which clustered and fused with each other to form electron-lucent, membrane-bound sacs around lipid droplets. The ultrastructural pattern of the excretory bladder is presented for the first time for an adult tapeworm. In C. brachycollis , the syncytial epithelial lining of both the distal and proximal bladder is a derivative of the tegumental distal cytoplasm of the posterior body surface. Variations in the structural organization of both bladder parts were observed in the kinds of luminal microtriches and in the presence of large cytoplasmic protrusions in the proximal bladder. In C. brachycollis , the lipid droplets are released into the proximal bladder lumen via 10 collecting descending excretory ducts. In adult mature monozoic caryophyllidean tapeworms, an accumulation of a large number of sarcoplasmic lipid droplets is observed and their presence in the protonephridial cyrtocytes is revealed at the posterior body end, where there are the reproductive organs and ducts.