(Panephemeroptera Euephemeroptera Euplectoptera Anteritorna Bidentiseta Furcatergaliae  
Fimbriatotergaliae Fossoriae Ephemera/fg9 - Hexagenia/fg1)

Nomen hierarchicum: Hexagenia/fg1 [f:1991; g:1863] (incl. Eatonica)

In circumscription fits:

 Hexagenia-complex: Koss & Edmunds 1974: 295

 subfam. Hexageniinae McCafferty 1991a: 354

 Hexagenia/fg1: Kluge 2004: 237

References. Koss & Edmunds 1974: *; Kluge 2004: * * *

Autapomorphies of Hexagenia/fg1.

(1) Paraglossae are stretched proximally-laterally in such a manner, that their stretched parts lie laterad of mentum and dorsad of palps (Eaton 18831888: Pl.63: 67).

(2) Maxilla has 2 canines only (unlike three initial ones in Ephemera/fg10); distal dentiseta [see Plesiomorphies of Ephemera/fg9] is vestigial, nearly invisible between proximal dentiseta and canines (only Hexagenia/g3 limbata [E.] and Eatonigenia/g1 chinei [H.] are examined).

(3) In imago and subimago of both sexes paracercus is vestigial. Non-unique apomorphy (see Index of characters [2.3.22]).

Character of Hexagenia/fg1 of unclear phylogenetic status. 

(4) Apex of larval fore tibia projects posteriad of tarsus base and forms outer-apical denticle and inner-apical projection, with incision between them (Eaton 18831888: Pl.63: 910). Similar in Palingenia/f2=g1 and Ichthybotus; possibly, symplesiomorphy [see Fossoriae (1)].

Plesiomorphies of Hexagenia/fg1. Larval frontal projection is not bipointed (unlike Ephemera/fg10): semicircular, conic or non-expressed. In imago and subimago: Mesonotal suture is moderately stretched posteriorly, and subimaginal mesonotal cuticle has pigmented areas of characteristic shape [see Fimbriatotergaliae (2)].

Size. Fore wing length 1030 mm.

Distribution. Nearctic, Neotropical, Afrotropical and Oriental Regions; probably, also Palaeogene of Palaearctic (see Denina in Ephemera/fg9 INCERTAE SEDIS).

The taxon Hexagenia/fg1 is divided into:

1. Hexagenia/fg2

1. 1. plesiomorphon Hexagenia/fg3 

1. 2. Pseudeatonica

2. Eatonica/g1

2.1. Litobrancha

2.2. Eatonica/g2 

2.3. Eatonigenia