Cuticular changes in fergusobiid nematodes associated with parasitism of fergusoninid flies

In the stylet-bearing nematode Fergusobia sp. (Tylenchida: Neotylenchidae), we hypothesize an additional separation (apolysis) and loss (ecdysis) of the adult cuticle, without the formation of a new cuticle, during the transition from the preparasitic to parasitic female. This pattern is in direct contrast to the characteristic 4-molt pattern accepted for most nematodes. Transmission electron microscope comparisons of the cuticle of an adult parthenogenetic female, male, and preparasitic female from the plant-parasitic phase of the fergusobiid life cycle revealed a relatively simple cuticle with an epicuticle, amorphous cortical/median zone, and a striated basal zone that is underlain by a relatively thin epidermis and striated somatic muscles. In contrast, the parasitic female from the adult fly was without its stylet and cuticle, the epidermis was enlarged, the outer edges of the epidermis were modified into microvilli, and the somatic muscles and esophagus were degenerate. The apparent hypertrophy and development of epidermal microvilli greatly expand the surface area of the parasitic female and presumably increase the nematode's ability to absorb nutrients directly through the epidermis from the host's hemolymph without cuticular interference.