ULTRASTRUCTURE AND CYTOCHEMISTRY OF PERIOSTRACUM AND MANTLE EDGE OF BIOMPHALARIA-GLABRATA (GASTROPODA, BASOMMATOPHORA)

Three layers of different electron density can be distinguished in the periostracum. Periostracal units of up to 900 nm length are merged in to the outer fibrous layer and binding of gold-labelled lectin-WGA ind icates the presence of chitin because it is labile to chitinase treatm ent. The periostracum is formed by the epithelia of the groove and the belt at the mantle edge. The distal and basal epithelium of the groov e consists mainly of type A cells with an extended Golgi apparatus and apical vesicles. The presence of peroxidase and phenol oxidase indica tes a function in tanning of the periostracum. In the proximal epithel ium of the groove, type B cells with protruding apices add more materi al for periostracum formation. Type C cells secrete single periostraca l units which are formed within single vesicles or larger vacuoles. Ty pe D cells secrete electron-dense vesicles which also contain WGA-posi tive material. The distal cells of the belt are characterized by predo minating strands of the rER while subapical vacuoles, to some of which WGA binds, dominate in the cells of the central part. In the belt, ph enol oxidase and peroxidase can be localized in cisternae of the rER a nd the Golgi apparatus. Numerous control incubations indicate that, in deed, two different enzymes are localized.