Sense receptors with electron-dense supporting structures, and centrioles in the nerve fibres of Gieysztoria and Rhinolasius (Platyhelminthes, Rhabdocoela).

The ultrastructure of two types of sense receptors each is described for Gieysztoria and Rhinolasius. In Gieysztoria, one receptor possesses a number of long microvilli, a cilium with a cross-striated rootlet, a septate desmosome, and an electron-dense band apical to the desmosome. The band forms a complex reticulate extension into the base of the receptor. The second receptor is without microvilli, has a cilium with a long cross-striated rootlet, and a septate desmosome with a short basal electron-dense extension or extensions which do not form a complete ring. In Rhinolasius, one receptor possesses a short bulbous cilium without a rootlet, with a septate desmosome of the pleated sheet (comb) type and a weakly developed electron-dense band beneath it. The second receptor has a long cilium with cross-striated rootlet, and a septate desmosome with a weakly developed electron-dense band apical to it. Centrioles were found in nerve fibres of both species.