ULTRASTRUCTURE OF THE SURFACE-STRUCTURES AND ELECTRON IMMUNOGOLD LABELING OF PEPTIDE IMMUNOREACTIVITY IN THE NERVOUS-SYSTEM OF PSEUDOTHORACOCOTYLA-INDICA (POLYOPISTHOCOTYLEA, MONOGENEA)

Transmission electron microscope studies of the tegument of the tropic al marine fish monogenean parasite Pseudothoracocotyla indica describe surface specialisations and detail the ultrastructure of the tegument and the haptor. The tegument consists of a syncytium, numerous electr on-dense granules, electron-lucent vesicles and large multivesicular b odies. The posterior tegumental syncytium is infolded to form tegument al ridges that are present on both the ventral and dorsal surfaces. A thin coat of glycocalyx is present on the tegument surface. In contras t, the tegumental syncytium of the haptor is relatively thin, containi ng electron-dense granules and various-sized electron-lucent vesicles. Exocytosis of the electron-dense and electron-lucent vesicles apparen tly occurs in the syncytium of the haptor and general body surface. Te gumental damage was observed on the dorsal surface in the mid-body reg ion and may possibly have been due to natural mechanical forces. The h aptor consists of electron-dense clamp sclerites embedded within a mat rix covered by the tegumental syncytium. The sclerites are connected t o each other and to the basal lamina by radially oriented muscle fibre s. The haptor is richly supplied with non-myelinated nerve axons. Both uniciliated and non-ciliated presumed sensory structures are present on the body surface and haptor. Uniciliated sensory structures were fo und mainly around the oral sucker. Groups of neurons and nerve process es containing neurosecretory vesicles were frequently observed in the vicinity of the clamps. Electron immunogold labeling studies demonstra ted that neuropeptide F [NPF (Moniezia expansa)] immunoreactivity was confined to electron-dense-cored neurosecretory vesicles in nerve fibr es from the posterior and haptor regions of the fluke.