Key to the males of Japanese Chrysotus

1. Femora mostly dark-green or brown ………………………………………………………………2 – Femora mostly yellow ………………………………………………………………………………5

2. Postocular setae black (Fig. 3 A–C) ………………… Ch. nudisetus Negrobov & Maslova, 1995 – Postocular setae pale ………………………………………………………………………………3

3. Face wide, more than 2 times wider than the length between ocellar bristles. Thorax and abdomen with purple tingle. Postpedicel large, approximately 2 times wider than long (Fig. 3 D–E) ………… ……………………………………………………..………….…… Ch. laesus (Wiedemann, 1817)

– Face narrow, narrower than the length between ocellar bristles. Thorax and abdomen green. Postpedicel small, approximately as long as wide ……………………………………………………4

4. Postpedicel triangular apically. Surstylus approximately 1.5 times longer than cercus. Apicoventral epandrial lobe well developed, broad oval, without excavation …………………… ……………………………………………… Ch. saigusаi Negrobov, Kumazawa & Tago sp. nov.

– Postpedicel oval apically. Surstylus approximately equal to cercus. Apicoventral epandrial lobe not developed, with excavation at apex (Fig. 3 F–G) …………………………………………………… ……………………………………………… Ch. kumazawai Negrobov, Maslova & Fursov, 2015

5. Fore coxae with black hairs …………………………………………………………………………6 – Fore coxae with white hairs …………………………………………………………………………7

6. Postpedicel longer than wide. Dorsal part of fore femora, middle femora in the middle part and apical third of hind femora dark. Phallus with oval process at apex on the left side ……… ……………………………………………… Ch. masunagai Negrobov, Kumazawa, Tago sp. nov.

– Postpedicel small, approximately as long as wide. Hind femora with dark spot at apex, the rest of femora yellow. Phallus with claw-shaped process at apex on the left side (Fig. 4 A–B) ………… ……………………………………………………… Ch. tagoi Negrobov, Maslova & Fursov, 2015

7. Hind tibia without long erect hairs. Hind tibia at apex without group of ventral hairs. Postpedicel large, triangular at apex (Fig. 4 C–D) ……………………………………… Ch. parilis Parent, 1926

– Hind tibiae and hind tarsi with long erect hairs, longer than tibia width. Hind tibia at apex with group of ventral hairs. Postpedicel small, oval apically (Fig. 4 E–F) ……… Ch. cilipes Meigen, 1824

Cladistic analyses

According to Capellari (2013), the absence of a small projection in the basal part of the epandrium represents the plesiomorphic character state. The combination of this character state with such character states as pale palpus, dark fore coxae, yellow hind tibia with short erect anteroventral hairs and short erect hairs on the first segment of hind tarsus separate the group of Ch. saigusai and Ch. tagoi from all other Japanese Chrysotus (Fig. 6). The species Ch. saigusai can be separated from Ch. tagoi by having anteroventral hairs on the entire length of find femora and mostly dark fore femora.

The presence of the epandrial projection is the typical character states of the species Ch. cilipes, Ch. parilis and Ch. masunagai sp. nov., they are, however, included in the group with Ch. saigusai sp. nov. and Ch. tagoi on the basis of the characters of face width, position of arista, cooler of postocular bristles, fore coxa, hind trochanter and morphology of CuA 1. Concerning the distinctive characters of the group including Ch. cilipes, Ch. parilis and Ch. masunagai sp. nov., in addition to the above mentioned, the following character states can be ascribed: yellow middle femora and dark basal part of hind femur. The morphological similarity between Ch. cilipes and Ch. parilis is sufficiently significant, while the relationship with Ch. masunagai sp. nov. is unstable.

The species Ch. laesus, Ch. nudisetus and Ch. kumazawai compose the group with the least stable internal connections. Their association is based on the similarity of color of fore, middle and hind femora and the absence of the anteroventral hairs on entire length of hind femur.