Cybistrinae, Sharp, 1880

Arce-Pérez, Roberto, Novelo-Gutiérrez, Rodolfo & Fery, Hans, 2021, Cybister (s. str.) poblanus sp. n. from Mexico and notes on other species of Cybistrinae (Coleoptera: Dytiscidae), Zootaxa 5061 (2), pp. 323-339 : 331-332

Key to species of Cybistrinae occurring in America north of Belize and Guatemala (including Cuba and the Bahamas)

Notes: The distribution area of some of the species studied may be considerably larger and extending far further south into the Neotropical region (see e.g. Arce-Pérez & Roughley 1999, Blanco Aller 2016, Brinck 1945, Hendrich et al. 2019, Megna & Sánchez-Fernández 2019, Miller 2013, Nilsson & Hájek 2021, Wilke 1920).

1. Males with only one metatarsal claw; females also with only one claw, but frequently with a short second claw. Posterior metatibial spur simple. Males with stridulatory file at base of metacoxae; females with file absent or weakly developed. Mesotarsomeres I–IV with two separate series of setae near apical margin (one posterodorsally and one posteroventrally; Fig. 3c ) in males and females.* ( Cybister ).......................................................................... 2

- Males and females with two metatarsal claws, though female posterior claw possibly rudimentary. Without stridulatory file at base of metacoxae. Mesotarsomeres I–IV with only one series of setae near apical margin (posteroventrally) in males and females.* ( Megadytes )................................................................................. 5

2. Apicoventral angle of metafemur sharply pointed ( Fig. 3b ); male median lobe in lateral view slender and evenly tapering to apex; in ventral view apex truncate and laterally expanded ( Figs 5g –5h ). Species from south-western USA and western Mexico........................................................................................... C. explanatus

- Apicoventral angle of metafemur not pointed ( Fig. 3a ); male median lobe different.................................. 3

3. Large species, TL 38 mm. Median lobe apically in lateral view moderately broad ( Fig. 4d ). Species so far known only from Puebla state, Mexico..................................................................... C. poblanus sp. n.

- Smaller species, TL <35 mm. Median lobe apically in lateral view broader ( Figs. 5a, 5d )............................ 4

4. Male median lobe as in Figs 5d–5e ; apex in lateral view truncate and more or less rectangular apicodorsally. Last abdominal ventrite of males and females more or less evenly rounded and flat. Species from Cuba, Bahamas and southern Florida ( USA).**............................................................................... C. occidentalis

- Male median lobe as in Figs 5a–5b ; apex in lateral view less truncate and rounded apicodorsally. Last abdominal ventrite of males truncate and with some transverse ridges ( Fig. 2b ); in females ventrite rounded and flat. Species from south-eastern Canada, large parts of USA, Bahamas and Mexico................................................ C. fimbriolatus

5. Posterior metatibial spur simple; elytra without lateral yellow margin. Smaller species, TL: 20–21 mm ( Megadytes s. str.).. 6

- Posterior metatibial spur bi- or trifurcate; elytra with lateral yellow margin. Larger species, TL: 27–43 mm .............. 7

6. Male protarsal palette more elongate, ratio long to short axis ca. 1.65; aedeagus as in Figs 6a–6c ; males with anterior protarsal claw longer and thicker than posterior, same with mesotarsal claws; females with elytra covered with striae, not smooth as in males; TL: 18,5– 22 mm. Species from USA (Florida), Mexico, Cuba, parts of Central and South America................................................................................................... M. (s. str.) fraternus

- Male protarsal palette less elongate, ratio long to short axis ca. 1.4; aedeagus as in Figs 6d–6f ; males with anterior protarsal claw longer, but only slightly thicker than posterior, differences in mesotarsal claws less distinct; females with elytra smooth as in males or with a few very fine strioles (striae) near base; TL: 19.5–22.5 mm. Species from Mexico [ Cuba?].................................................................................................... M. (s. str.) flohri

7. Posterior metatibial spur trifurcate. TL: 27–29 mm ( Megadytes Trifurcitus). Species from Mexico.......... M. (T.) fallax

- Posterior metatibial spur bifurcate. TL: 36–43 mm ( Megadytes Bifurcitus)........................................ 8

8. Median lobe of aedeagus in lateral and ventral view as in Figs 6g –6h ; TL: 36–42.5 mm. Species from Mexico, the Caribbean, large parts of Central and South America to southern Brazil..................................... M. (B.) lherminieri

- Median lobe of aedeagus in lateral and ventral view as in Figs 6i–6j ; TL: 39–43 mm. Species from Mexico, parts of South America until south-eastern Brazil; most probably also from Central America......................... M. (B.) magnus

Figures

FIGURES 2a–1c: a, b: Last abdominal ventrite of: (a) Cybister poblanus sp. n.; (b) C. fimbriolatus; c: oblique view on head of Cybister poblanus sp. n.; d–e: last left metatarsomere of male of (d) Megadytes lherminieri (two claws); (e) Cybister poblanus sp. n. (one claw).

FIGURES 3a–3c. a, b: Part of venter showing ridges on metacoxae (stridulatory organ) and apicoventral angle of metafemora of: (a) Cybister poblanus sp. n.; (b) C. fimbriolatus; c: posterior surface of right mesotarsus of C. fimbriolatus; mesotarsomeres I–IV with two separate series of setae near apical margin: one posterodorsally (on top) and one posteroventrally (on bottom); some further setae removed for better visibility of the setae under consideration.

FIGURES 4a–4f: Cybister poblanus sp. n.: a–c: complete aedeagus in (a) ventral view; (b) dorsal view; (c) nearly lateral view; d–e: median lobe in (d) lateral view; (e) ventral view; f: right paramere.

FIGURES 5a–5i: Median lobe in lateral view (a, d, g), in ventral view (b, e, h) and paramere (c, f, i) of: (a–c) Cybister fimbriolatus; (d–f) C. occidentalis; (g–i) C. explanatus.

FIGURES 6a–6j: a–f: Median lobe in lateral view (a, d), ventral view (b, e) and paramere (c, f) of (a–c) Megadytes fraternus; (d–f) M. flohri; g–j: median lobe in lateral view (g, i) and ventral view (h, j) of (g, h) M. lherminieri and (i, j) M. magnus. Figures 6g–6j adapted from figs 5 and 6 in Hendrich et al. (2019) (licensed under a Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0).