Key for the males of the Perlodini genera

Two genera included in the PSF (DeWalt et al. 2022) as belonging to Perlodini, not treated herein: Hedinia Navás, 1936 is known only from the female holotype, while Protarcys Klapálek, 1912 is under redescription and assessment of its affinity. Recent studies proved that Rauserodes Zwick, 1999 is a junior synonym of Perlodinella Klapálek, 1912 (Huo et al. 2022a), and Sinoperlodes Chen, 2020 is a junior synonym of Filchneria Klapálek, 1908 (Huo et al. 2022b).

1 Tergum X not divided into hemiterga (e.g., figs. 3A, 7A in Huo et al. 2022a)...................................... 2

- Tergum X divided into hemiterga (e.g., Fig. 7).............................................................. 7

2 Paraproct modified into caudally directed, hook-like lobe; tergum X with lightly sclerotized medial field (figs. 132, 135 in Teslenko & Zhiltzova 2009)................................................... Diura Billberg, 1820 (Holarctic)

- Paraproct not modified into hook-like lobe; tergum X entirely sclerotized or with lightly sclerotized field of variable extent. ................................................................................................... 3

3 Eversible epiproct present (fig. 14E in Huo et al. 2022a)......................... Perlodinella Klapálek, 1912 (China)

- Epiproct is lacking.................................................................................... 4

4 Eversible paraproct lobe with distinct sclerotized process (e.g., fig. 12 in Teslenko & Palatov 2020).................... 5

- Eversible paraproct lobe membranous, or only with slight sclerotization (e.g., fig. 9 in Huo et al. 2022b)................ 6

5 Paraproct with truncated knob (fig. 9 in Teslenko & Palatov 2020)............ Zhiltzovaia Özdikmen, 2008 (Central Asia)

- Paraproct without knob (figs. 5, 8, 25 in Teslenko 2015)............................................................................................ Megaperlodes Yokoyama, Isobe & Yamamoto, 1990 (Pacific East Palaearctic)

6 At least one of terga 8–10 with sensilla basiconica patches (figs. 3B, 9A in Huo et al. 2022b).............................................................................. Filchneria Klapálek, 1908 (Caucasus and East Palaearctic)

- Terga lack sensilla basiconica (figs. 129B–C in Kis 1974)......................... Perlodes Banks, 1903 (Palaearctic)

7 Furcal pit connecting anteriorly to arms of mesosternal ridge (Fig. 1).......................... Habaek gen. n. (Korea)

- Furcal pit connecting posteriorly to arms of mesosternal ridge, or the connection is obscure (figs. 36A–D in Ricker 1952).. 8

8 Epiproct tip with arrow-like apex (e.g. figs. 8.33, 8.49 in Kondratieff 2004)....................................... 9

- Epiproct tip different................................................................................. 11

9 Furcasternum with longitudinal medial ridge (fig. 36D in Ricker 1952)............ Isogenoides Klapálek, 1912 (Nearctic)

- Furcasternum lacks medial ridge........................................................................ 10

10 Submental gill distinctive (compare Fig. 4)............................... Hydroperla Frison, 1935 (Eastern Nearctic)

- Submental gill lacking..................................................... Dictyogenus Klapálek, 1904 (Alps)

11 Epiproct tip modified into a long, asymmetrical curved process (figs. 55–56 in Teslenko & Zhiltzova 2009).................................. Levanidovia Teslenko & Zhiltzova, 1989 (in: Zhiltzova & Teslenko 1989) (Pacific East Palaearctic)

- Epiproct tip symmetrical.............................................................................. 12

12 Hemitergum with swollen apex, armed with sensilla basiconica and/or dense, long setae (e.g., figs. 8.9–10 in Kondratieff 2004)............................................................................................. 13

- Hemitergum with widely rounded but not swollen apex, sensilla basiconica is usually lacking....................... 17

13 Lateral stylet of epiproct absent (e.g., figs 8.10, 8.13 in Kondratieff 2004)....................................... 14

- Lateral stylet of epiproct present (e.g., fig. 3C in Zwick 1971)................................................ 15

14 Submental gill distinctive; epiproct tip pointed (figs. 8.10, 8.13 in Kondratieff 2004).................................................................................................. Helopicus Ricker, 1952 (Eastern Nearctic)

- Submental gill is lacking; epiproct tip swollen (figs. 1–3 in Stark et al. 1986).......................................................................... Guadalgenus Stark & González del Tánago, 1986 (in: Stark et al. 1986) (Iberia)

15 Epiproct tip with distinctive, hook-like apex (fig. 4 in Kondratieff et al. 2007)..................................................................................................... Chernokrilus Ricker, 1952 (Western Nearctic)

- Epiproct tip blunt or with short, acute tip................................................................. 16

16 Hemiterga widely separated in the medial portion of the segment; epiproct tip acute (figs. 64, 67–68 in Teslenko & Zhiltzova 2009)................................................................. Isogenus Newman, 1833 (Palaearctic)

- Hemiterga narrowly separated in the medial portion of the segment; epiproct tip blunt (figs. 3A–C in Zwick 1971)............................................................................ Besdolus Ricker, 1952 (West Palaearctic)

17 Lateral stylet of epiproct absent (e.g., figs. 8.68, 8.72–73 in Kondratieff 2004)................................... 18

- Lateral stylet of epiproct present (e.g., figs. 8.58, 8.61 in Kondratieff 2004)...................................... 19

18 Epiproct tip narrow and erect (figs. 8.69, 8.73 in Kondratieff 2004)................ Yugus Ricker, 1952 (Eastern Nearctic)

- Epiproct tip membranous and coiled up (fig. 17F in Inada 1996)...............unnamed genus sensu Inada (1996) (Japan)

19 Lateral stylet of epiproct hooked at apex; epiproct tip with reddish setae (figs. 8.58, 8.61 in Kondratieff 2004).............................................................................. Malirekus Ricker, 1952 (Eastern Nearctic)

- Lateral stylet of epiproct not hooked; epiproct tip without reddish setae......................................... 20

20 Submental gill absent; lateral stylet truncate (figs. 8.64–65 in Kondratieff 2004)............................................................................................. Oconoperla Stark & Stewart, 1982 (Eastern Nearctic)

- Submental gill long; lateral stylet acute ……………………………………………………………..21

21 Head entirely black; epiproct tip with longitudinal dorsal sclerite strip not reaching apex (figs. 9A–B, G in Inada 1996)................................................................................. Tadamus Ricker, 1952 (Japan)

- Head with yellow pattern; epiproct tip with longitudinal dorsal sclerite strip reaching apex (figs. 1, 4–6 in Bottorf et al. 1989).......................................................... Susulus Bottorf, Stewart & Knight, 1989 (California)