Morphological description of four species belonging to the genus Nigrobaetis (Ephemeroptera: Baetidae) from Japan

We associated imagoes and nymphs of four Nigrobaetis species from Japan and described their morphological characters. We found that N. sp. P comprised two Nigrobaetis species in Kanto Plain and in Ishigaki Island, which we described as N. apterus Fujitani n. sp. and N. ishigakiensis Fujitani n. sp., respectively. We also described N. sp. I as N. latus Fujitani n. sp. We recorded N. acinaciger (Kluge), the nymph of which had been confused with N. chocoratus (Gose), from Japan for the first time. We provide identification keys for eight Nigrobaetis species of Japan.