Ultrastructure of the acanthella of Paratenuisentis ambiguus (Acanthocephala)

Abstract

The fine structure of the early acanthella of Paratenuisentis ambiguus (Eoacanthocephala) was investigated. This developmental stage is characterised by losing its ability to move and by differentiation of adult structures. The frontal syncytium, present in the first developmental stage (the acanthor), is lost, while the epidermis and central syncytium persist. The epidermis of the acanthella contains a number of giant nuclei that are arranged into 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. Formation of the hooks takes place within these strands. In all investigated stages no extracellular materials were observed. Posterior of the uncinogenous bands lies the brain anlage and the primordia of the reproductive system. Neither a sense organ nor a nervous system were found.

Transcriptome Data Reveal Syndermatan Relationships and Suggest the Evolution of Endoparasitism in Acanthocephala via an Epizoic Stage

“…Moreover, this scenario implies that the indirect development of acanthocephalans, involving the metamorphosis from a larval stage (acanthor) to a young adult (acanthella; called cystacanth when encysted) within the intermediate host [82], represents an evolutionary novelty of acanthocephalans. It is obvious that morphological traits such as the rostellar apparatus of the acanthor, a proboscis including hooks and specific musculature of infectious acanthella and adults, and a reduced digestive tract throughout all developmental stages are acanthocephalan autapomorphies that most probably evolved in the context of their endoparasitic lifestyle [18], [22], [50], [79], [83] (Fig. 4).…”