Ultrastructure of the body wall of Cystidicoloides ephemeridarum (Nematoda, Cystidicolidae) in relation to the histopathology of this nematode in salmonids.

Light, scanning and transmission electron microscope examinations of adult Cystidicoloides ephemeridarum nematodes, parasitic in the stomach of brown trout (Salmo trutta fario L.), revealed that the body wall is composed of a cuticle, a hypodermis and longitudinally oriented somatic musculature. The body cuticle is composed of a trilaminated epicuticle, an outer and inner cortical zone, a median zone with globular bodies and a basal zone consisting of three subzones. Massive cuticle in the three zones and an osmiophilic lining is present in the buccal capsule. Armament is absent both from the buccal capsule and the head end. The surface of the body is transversely striated with cortical annuli. The only specialized attachment devices of C. ephemeridarum are the flexible overlapping margins of the annuli which are elongated in the first third of the body. Together with the sucking pressure of the oesophagus, they seem to play a role in the penetration and mechanical damage of the host's tissue. The hypodermis appears to be syncytial. Up to 300 worms were present in the bolus of food consumed by the host, or attached by their head ends in the lamina epithelialis, which resulted in localized disruptions of the mucosal epithelium with no inflammation. Infection with C. ephemeridarum seems to be a temporary, season-dependent event of mild pathogenicity.