First Information on the Ultrathin Structure of the Tegument of the “Cystacanth” in Acanthocephala Neoechinorhynchus beringianus Mikhailova et Atrashkevich, 2008 (Eoacanthocephala, Neoechinorynchidae)

The ultrastructure of the metasoma tegument of the developing acanthocephalan Neoechinorhynchus beringianus (Neoechinorhynchidae) was studied for the first time for representatives of the class Eoacanthocephala. The completely developed acanthellae of this species were shown to have no cyst, which is a characteristic feature of cystacanths at these stages of development in other acanthocephalan classes, and protection against the host response is provided by a thick layer of glycocalyx on the tegument surface. The tegument is represented by a typical symplast and includes a standard set of layers (cross-striated, felt-fibrous, radial-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 permit us to use the term “cystacanth” concerning them.