Key to known species for adult males* of Sympotthastia worldwide (based on Liu et al. 2016) 1. Anal point absent..................................................................................... 2 - Anal point present..................................................................................... 4 2. Anal lobe of wing reduced, megaseta absent (Liu et al. 2016: Figs. 10–15)........... S. wuyiensis Liu, Ferrington & Wang - Anal lobe of wing well developed, megaseta present......................................................... 3 3. Phallapodeme curved, S-shaped; gonostylus gradually expanded anteriorly (Ghaderi et al. 2024: Figs. A–E).............................................................................. S. golalae Ghaderi, Namayandeh & Karimian - Phallapodeme boot-shaped, distal end extending downwards to the middle of gonocoxite; gonostylus widest in the middle and narrower towards the apex........................................................... S. annularis Fu, sp. nov. 4. Anal point sclerotized, narrow, long and slender............................................................. 5 - Anal point tubercle-like; apex of tubercle with or without strong setae........................................... 9 5. Aedeagal lobe distally expanded, reniform or knob-like....................................................... 6 - Aedeagal lobe not distally expanded, sigmoid or straight...................................................... 8 6. Median volsella bare, apical margin finely serrated (Tuiskunen 1986: Figs. 2–3)................... S. huldeni Tuiskunen - Median volsella spiniferous............................................................................. 7 7. AR 3.38–4.26; prealars 14; aedeagal lobe distally knob-like (Makarchenko 1994: Figs. 10–13)..... S. takatensis (Tokunaga) - AR 2.90–3.10; prealars 23–31; aedeagal lobe distal reniform (Makarchenko 1985: Fig. 228)...... S. repentina Makarchenko 8. Scutellum with 48 setae; prealars 15; aedeagal lobe distally sigmoid (Doughman 1985: Figs. 1–3)..... S. diastena (Sublette) - Scutellum with 24 setae; prealars 4; aedeagal lobe distally straight (Doughman 1985: Fig. 13; Makarchenko 1985: Fig. 227)..................................................................................... S. fulva (Johannsen) 9. Aedeagal lobe very broad, converging to point distally; phallapodeme short, not extending beyond aedeagal lobe (Makarchenko 1994: Figs. 1 –4)............................................................... S. gemmaformis Makarchenko - Aedeagal lobe not as above; phallapodeme long, extending much beyond aedeagal lobe............................ 10 10. Anal point tubercle-like, without strong setae (Serra-Tosio 1968: Fig. 2).............................. S. zavreli Pagast - Anal point reduced to a simple seta or consists of two strong setae arising at the tip................................ 11 11. AR higher, ca. 3.0; clypeus with 11 setae (Doughman 1985: Figs. 11–12)...................... S. macrocera Serra-Tosio - AR lower, ca. 1.60–1.75; clypeus with 4–5 setae (Doughman 1985: Figs. 7–10).................. S. spinifera Serra-Tosio * S. bicolor (Tokunaga, 1937) is not included in this key because the species description is based on the adult female only.

Published as part of Fang, Xiangliang, Shangguan, Jingru & Fu, Yue, 2025, Sympotthastia annularis sp. nov. from Oriental China (Diptera: Chironomidae: Diamesinae) with a worldwide key, pp. 571-578 in Zootaxa 5717 (4) on pages 576-577, DOI: 10.11646/zootaxa.5717.4.5, http://zenodo.org/record/17891010