Ultrastructure and overall organization of ligament sac, uterine bell, uterus and vagina in Paratenuisentis ambiguus (Acanthocephala, Eoacanthocephala) – the character evolution within the Acanthocephala

Abstract

AbstractAs an adaptation to their endoparasitic lifestyle, Acanthocephala (Palaeacanthocephala, Eoacanthocephala, Polyacanthocephala, Archiacanthocephala) have evolved a highly specialized reproductive system. Most of our present knowledge of the efferent duct system of the female is based on palaeacanthocephalan and archiacanthocephalan representatives. In order to provide a basis for further elucidating the phylogenetic relationships within the Acanthocephala, we herein describe ultrastructure and overall organization of the ligament sac and efferent duct system in females of Paratenuisentis ambiguus (Eoacanthocephala, Neoechinorhynchida). Only one ligament sac was found. The uterine bell consists of two contractile binucleate syncytia (bell wall syncytium, lateral pocket syncytium), two pairs of contractile cells (lappet cells, uterine bell retractors) and three pairs of noncontractile cells (median cells). The contractile uterus bears four nuclei. The vagina is composed of a syncytial epithelium (four nuclei) and two binucleate sphincters. A comparison of the present findings with literature data leads to the following conclusions: except for the uterine bell retractors, the uterine bell components found in P. ambiguus can be assumed to be autapomorphies for the Acanthocephala. The sheathing syncytium and median dorsal cell belong to the basal pattern (sensu ground pattern) of a palaeacanthocephalan subclade termed the Echinorhynchus‐group in the present study. The median oviduct syncytium and paired uterine bell retractors can be assumed to be basal pattern characteristics of the Archiacanthocephala and Neoechinorhynchida, respectively. The study includes a tabular survey of terminological synonyms used in the literature.