Aciliini

Alarie, Yves, Michat, Mariano C. & Dettner, Konrad, 2025, Testing the monophyly of the tribe Aciliini and the phylogenetic position of the Afrotropical genus Aethionectes Sharp, 1882 (Coleoptera: Dytiscidae, Dytiscinae) based on larval morphology, Zootaxa 5620 (2), pp. 335-352 : 344

Identification key to instar III larvae of World genera of Aciliini ( Coleoptera : Dytiscidae , Dytiscinae )

Instar III larvae of Aciliini are readily differentiate from instars I and II by the presence of spiracular openings on each side of mesothorax and abdominal segments I–VII. The key does not include the Afrotropical Tikoloshanes , which larvae have yet to be described.

1. Specimens from the Holarctic region, not found in Southwest U.S.A............................................. 2

- Specimens not from the Holarctic region, exceptionally found in Southwest U.S.A................................. 3

2. Prementum median process Y-shaped (= bifid), at least with an apical incision; primary pores MNa and MNb articulated at about same level on mandible; GA/MP1> 2.00........................................................ Acilius

- Prementum median process unifid, lacking an apical incision (as in Figs 9–10 , 18 ); primary pore MNa inserted distally to pore MNb on mandible (as in Fig. 5 ); GA/MP1 <1.50................................................. Graphoderus

3. Specimens from the Neotropical and Southwest U.S.A. region...................................... Thermonectus

- Specimens from either the Australian, Oriental or Afrotropical regions........................................... 4

4. Meso- and metacoxa lacking anterior hair-like setae; metatrochanter lacking proximal hair-like secondary setae; stipes with two rows of spine-like setae dorsally; HL/HW> 1.70; MP3/MP2> 1.70; GA/MP1 <2.50; LAS/HW> 1.60; U/HW = 0.20............................................................................................... Rhantaticus

- Meso- and metacoxa with a row of anterior hair-like setae; metatrochanter with a variable number of proximal hair-like secondary setae (as in Figs 11–12 ); stipes with one row of spine-like setae dorsally ( Fig. 7 ); HL/HW <1.50; MP3/MP2 <1.60; GA/MP1> 1.70; LAS/HW <1.40 U/HW = 0.40............................................................ 5

5. Two pairs of dorsal stemmata very large ( Figs 1 , 16 ); PMP/LP1 <0.40; MP/LP = 0.80; Afrotropical......... Aethionectes

- Two pairs of dorsal stemmata smaller (cf., Fig. 15 in Alarie et al. 2023b); PMP/LP1> 0.60; MP/LP = 0.60; Oriental and Australian................................................................................ Sandracottus

Figures

FIGURES 7–10. Aethionectes oberthueri (Régimbart, 1895), instar III: 7. maxilla, dorsal aspect; 8. maxilla, ventral aspect; 9. labium, dorsal aspect; 10. labium, ventral aspect. LA, labium; MX, maxilla; MP, maxillary palpomere. Numbers and lowercase letters refer to primary setae and pores, respectively. Scale bars = 0.2 mm.

FIGURES 16–19. SEM of Aethionectes oberthueri (Régimbart, 1895), instar III: 16. head, dorsal view; 17. lamellae clypeales; 18. prementum and stipes, ventral view; 19. labial palpus, dorsal view.

FIGURES 1–6. Aethionectes oberthueri (Régimbart, 1895), instar III: 1. head capsule, dorsal aspect; 2. head capsule, ventral aspect; 3. antenna, dorsal aspect; 4. antenna, ventral aspect; 5. mandible, dorsal aspect; 6. mandible, ventral aspect. A, antennomere; AN, antenna; MN, mandible; sp, spinula. Numbers and lowercase letters refer to primary setae and pores, respectively. Scale bars = 0.5 mm (Figs 1–2); 0.2 mm (Figs 3–6).

FIGURES 11–15. Aethionectes oberthueri (Régimbart, 1895), instar III: 11. metathoracic leg, anterior surface; 12. metathoracic leg, posterior surface; 13. abdominal segment VIII, dorsal aspect; 14. abdominal segment VIII, ventral aspect; 15. urogomphus, dorsal aspect. AB, abdominal segment VIII; CO, coxa; FE, femur; TA, tarsus; TI, tibia; TR, trochanter; UR, urogomphus. Numbers and lowercase letters refer to primary setae and pores, respectively. Scale bars = 0.5 mm (Figs 11–12); 0.2 mm (Figs 13–15).