Ultrastructure of presumed sensory receptors in the scolex of adult Proteocephalus exiguus (Cestoda, Proteocephalidea)

Abstract

The ultrastructure of six types of putative sense receptors including three nonciliate (Types I–III) and three ciliate (Types IV–VI) types found in the tegument of the scolex of adult Proteocephalus exiguus has been described for the first time. Type I has a simple tegumental sensory ending, containing one electron-dense collar, circular septate desmosome, electron-lucent vesicles and microtubules. Type II is represented by a receptor with a large rootlet. Type III is a receptor with a very long cross-striated rootlet, with two electron-dense collars and septate junction. The ciliated receptors differ in the length of the cilium, in the number of electron-dense collars and in the shape of sensory bulb. A comparison of structural features of receptors in different systematic groups within Platyhelminthes is made.