Ultrastructure studies of preadult Proteocephalus longicollis (Cestoda, Proteocephalidea): transmission electron microscopy of scolex sensory receptors

The ultrastructure of five types of presumed sensory receptors in the scole x of preadults of Proteocephalus longicollis is described. Two types of non ciliate sensory receptors are situated on the inner surface of the lateral sucker. They differ from each other in the shape, presence, or absence of a large rootlet, electron-dense collars, desmosomes, microtubules, and/or ve sicles. In addition, three types of ciliate sensory receptors are found alo ng the edges of the lateral suckers. They can be differentiated by the leng th of the cilium, by the number of electron-dense collars tone or two), and by types of vesicles. Four types of vesicles were found inside the ciliate sensory receptors. One type of ciliate sensory receptor occurring in pread ults differs markedly from any of the sensory receptors previously describe d in adult P. longicollis.