The genus Acoenonia, revised twice in recent years (Jaschhof 1998; Jaschhof & Jaschhof 2009), previously included four species, two Palearctic (A. europaea Mamaev, A. sidorenkoi Fedotova) and two Holarctic (A. nana Meyer & Spungis, A. perissa). Acoenonia sidorenkoi remains an enigmatic Far Eastern species, whose description (Fedotova 2004: 566ff.) is so superficial that it cannot be related to the congeners. Two new Acoenonia are described here, both generally similar to species named in the past.
Key to species (males). Characters of the male genitalia should be used for identifying species, because other male characters, such as the numbers of flagellomeres and palpal segments, might vary within a species and female characters are only known of A. europaea and A. nana. The key presented here includes A. sidorenkoi on the assumption that Fedotova’s (2004) description of this species is correct.
1 Gonostylus without tooth..................................................................... A. sidorenkoi
- Gonostylus with dorsal or apicodorsal tooth............................................................... 2
2 Membranous parts of aedeagus covered with normal microtrichia......................................... A. nana
- Membranous parts of aedeagus covered with small triangular spines............................................ 3
3 Apex of ejaculatory apodeme broad, bifurcate............................................................. 4
- Apex of ejaculatory apodeme narrowly rounded............................................................ 5
4 Apical fork of ejaculatory apodeme wide, enclosing innumerable small spines. Gonostylus with dorsobasal lobe. A. europaea
- Apical fork of ejaculatory apodeme narrow, with about 15 larger spines. Gonostylus without dorsobasal lobe..... A. baltica
5 Ejaculatory apodeme excessively broad basally..................................................... A. perissa
- Ejaculatory apodeme not broadened basally...................................................... A. ulleviensis