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 t he adult cuticle, without the formation of a new cuticle, during the transi tion from the preparasitic to parasitic female. This pattern is in direct c ontrast to the characteristic 4-molt pattern accepted for most nematodes. T ransmission electron microscope comparisons of the cuticle of an adult part henogenetic female, male, and preparasitic female from the plant-parasitic phase of the fergusobiid life cycle revealed a relatively simple cuticle wi th an epicuticle, amorphous cortical/median zone, and a striated basal zone that is underlain by a relatively thin epidermis and striated somatic musc les. In contrast, the parasitic female from the adult fly was without its s tylet and cuticle, the epidermis was enlarged, the outer edges of the epide rmis were modified into microvilli, and the somatic muscles and esophagus w ere degenerate. The apparent hypertrophy and development of epidermal micro villi greatly expand the surface area of the parasitic female and presumabl y increase the nematode's ability to absorb nutrients directly through the epidermis from the host's hemolymph without cuticular interference.