Ultrastructure of the acanthella of Paratenuisentis ambiguus (Acanthocephala)

The fine structure of the early acanthella of Paratenuisentis ambiguus (Eoa canthocephala) was investigated. This developmental stage is characterised by losing its ability to move and by differentiation of adult structures. T he frontal syncytium, present in the first developmental stage (the acantho r), is lost, while the epidermis and central syncytium persist. The epiderm is of the acanthella contains a number of giant nuclei that are arranged in to several small groups. The central syncytium is subdivided into different masses, containing nuclei that will give rise to the organs of the adult. The 'uncinogenous bands' extend into the anterior body of the acanthella. F ormation of the hooks takes place within these strands. In all investigated stages no extracellular materials were observed. Posterior of the uncinoge nous bands lies the brain anlage and the primordia of the reproductive syst em. Neither a sense organ nor a nervous system were found.