Argentophilic structures as a diagnostic criterion for the discrimination of species of the genus Gyrodactylus von Nordmann (Monogenea)

The mapping of argentophilic surface sensory structures (chaetotaxy) is a technique which has contributed to the taxonomy of larval digeneans. Four species of Gyrodactylus from four different hosts (Salmo salar, Gasterosteus aculeatus, Poecilia reticulata and Carassius auratus) were investigated using this technique in order to ascertain its usefulness in distinguishing species of this monogenean genus. A formula for the arrangement of the natural aggregations of sensilla similar to those prepared for cercariae is proposed. Although the greatest concentration of sensilla occur 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 have been constructed to demonstrate these differences. It is concluded that chaetotaxy shows potential as a simple and reliable method of distinguishing species of this genus.