Argentophilic structures as a diagnostic criterion for the discrimination of species of the genus Gyrodactylus von Nordmann (Monogenea).
Four species of Gyrodactylus from the fins of 4 different hosts (G. derjavini from Salmo salar in Scotland, G. gasterostei from Gasterosteus aculeatus in England, Gyrodactylus longoacuminatus from Carassius auratus in England and G. turnbulli from Poecilia reticulata, held in aquaria at the Natural History Museum in London) were investigated using chaetotaxy in order to ascertain its usefulness in distinguishing species of this monogenean genus; 50 worms from each collection site were stained with silver nitrate and examined. The patterns of sensilla were mapped, and the species of Gyrodactylus confirmed from the morphology of the opisthaptoral sclerites. A formula for the arrangement of the natural aggregations of sensilla, similar to those prepared for cercariae, is proposed for each species. Although the greatest concentration of sensilla occurs adjacent to the anterior extremity of the body, it is the region just posterior to the pharynx which most readily permits the discrimination of Gyrodactylus spp. based on the number and spatial configuration of these sensilla. Maps were constructed to demonstrate these differences. It is concluded that chaetotaxy shows potential as a simple and reliable method of distinguishing species of this genus.