A new species of Heterocotyle (Monogenea: Monocotylidae), a gill parasite of the diamond stingray Hypanus dipterurus (Myliobatiformes: Dasyatidae) from the Peruvian coastal zone.

INTRODUCTION: A new monogenean, Heterocotyle margaritae n. sp. (Monocotylidae: Heterocotylinae), is described based on specimens collected from the gills of the diamond stingray, Hypanus dipterurus (Jordan & Gilbert, 1880) (Myliobatiformes: Dasyatidae) captured off the South Pacific coast, Lima Region, Peru. MATERIALS AND METHODS: Monogeneans were fixed in hot 4% formalin, observed and measured as permanent mounts stained with Gomori's trichrome, and mounted in Canada balsam. Drawings were made with the aid of a drawing tube. RESULTS: The new species is distinguished from all congeners mainly by having a funnel-shaped male copulatory organ, spatulate distally with lateral folds and by its club-shaped accessory piece. The most similar congener, H. americana Hargis, 1955, resemble H. margaritae n. sp. regarding the general structure of the male copulatory organ (funnel-shaped with an accessory piece). However, besides other features, the new species differ from H. americana by having an accessory piece without a dorsal button (vs an accessory piece with a dorsal button in H. americana). CONCLUSIONS: This is the first report of a member of Heterocotyle Scott, 1904 in the Southeastern Pacific Ocean. The present finding brings to 20 the number of known species of Heterocotyle, and represents the fifth described monogenean species from Hypanus dipterurus.