Ultrastructure of the buccal complex of Polylabroides australis (Monogenea, Polyopisthocotylea, Microcotylidae).

The two buccal suckers have a largely muscular septum each and, near the pharynx, dorsal swellings ("valve apparatus") extend into the lumen of the suckers. In the posterior parts of the suckers, the tegument forms a "rim" containing much electron-dense material. The walls of the suckers are mainly formed by muscle filaments, and there are several large vacuolated masses containing lipid (?) globules and vacuoles. The most anterior part of the pharynx contains a thick layer of electron-dense material which also lines the pharyngeal wall facing the lumen. Nine types of sensory receptors, all with electron-dense collars, were observed in the tegument near the suckers, in the mouth cavity and its extensions, and in the anterior part of the pharynx. Some are uniciliate, one is biciliate, one multiciliate, and two (including the pharyngeal receptors) are nonciliate. The greatest variety of receptors, including receptor complexes consisting of three receptor types, is found in a posterior ventral extension of the mouth cavity. It is suggested that this extension can be protruded into the suckers, facilitated by numerous muscle filaments in the tissue around it.--Septate suckers, mouth cavity and its extension, valve apparatus and pharynx are likely to form a functional whole, the "buccal complex", used for food intake.