First knowledge on the ultrathin structure of the tegument “Cystacanth” of the acanthocephala <i>Neoechinorhynchus beringianus</i> Mikhailova, Atrashkevich, 2008 (Eoacanthocephala, Neoechinorynchidae)

For the first time, the ultrastructure of the metasoma tegument of the developing acanthocephalan Neoechinorhynchus beringianus (Neoechinorhynchidae) was studied at representatives of the Eoacanthocephala class. Completely developed acanthellae of this species were shown to have no cyst, which is a characteristic feature of cystacanths of similar development stages in representatives of other acanthocephalan classes; and the protection function from the host response is performed by a thick layer of glycocalyx on the tegument surface. The tegument is represented by a typical symplast, including a standard set of layers (cross-striated, felt-fibrous, radially fibrous and tubular), and is underlain by a basal plate and two layers of muscles. The absence of a cyst in the completely developed acanthellae under study does not allow using the term “cystacanth” concerning them.