Dactylogyrus olfactorius n. sp. (Monogenea, Dactylogyridae) from the olfactory chamber of the fathead minnow, Pimephales promelas Rafinesque (Cyprinidae).

Dactylogyrus olfactorius n. sp. (Monogenea) is described from the olfactory chamber of the fathead minnow Pimephales promelas Rafinesque in Alberta, Canada. The new species resembles Dactylogyrus bychowskyi Mizelle, 1937, D. bifurcatus Mizelle, 1937 and D. simplexus Mizelle, 1937, all parasites of Pimephales spp. in North America, in overall size and shape of the anchors and hooks, and in having a male copulatory complex with a tapered tubular penis and bifurcate accessory piece. Diagnostically, D. olfactorius n. sp. has relatively small anchors, hooks of anchor length, and a thin, long dorsal bar and no apparent ventral bar nor 4A hooks. Scanning electron microscopy revealed the body tegument of D. olfactorius n. sp. to be microvillous and in shallow annular folds, while that of D. bifurcatus, occurring on host gills of the same fish, was avillous and in gill-like folds dorsally and ventrally. Partial 28S rDNA sequences revealed significant differences between the two species, supporting establishment of D. olfactorius n. sp. and dispelling the possibility of ecophenotypic effects of site of attachment on morphology.