CLADOENDESIS OF EPHEMEROPTERA

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Autapomorphy of Bidentiseta.

(1) Maxilla has 2 dentisetae only – distal and proximal ones [instead of initial 3 dentisetae – see Anteritorna (2)]. In some specialized representatives of Bidentiseta further reduction of dentisetae takes place, thus only one (proximal) dentiseta can be retained, or dentisetae disappear at all (see Index of characters [1.1.37]). Among Bidentiseta more than two dentisetae nearly newer occur; an exception is made by Coloburiscus/fg1, where number of dentisetae is indeterminate and in specimens of the same species can be 2 or 3. Number of dentisetae less than three, besides Bidentiseta, is present also in some specialized taxa, which we attribute to Tridentiseta: specialized filtering maxilla of Ameletus/fg1 bears a single vestigial dentiseta, and specialized for carnivorism maxilla of Acanthametropus/fg2 bears two canine-like dentisetae. Thus, a formal number of dentisetae does not allow to divide all Anteritorna into Bidentiseta and Tridentiseta. The idea that Bidentiseta is a holophyletic taxon, is based on the fact that in each of evidently holophyletic taxa constituting the taxon Bidentiseta, the presence of two dentisetae is an initial condition: two dentisetae are present in many Eusetisura (Kluge 2004: Fig.44:D), Heptagennota (Kluge 2004: Fig.54:M, 58:F-H, 61:H, 65:F), Fimbriatotergaliae (Kluge 2004: Fig.68:C), Ephemerella/fg1 (Kluge 2004: Fig.92:B, 92:F,H, 93:D, 95:C, 96:C) and primitive representatives of Leptophlebia/fg1 (Kluge 2004: Fig.106:C,G). In many cases these maxillae with two dentisetae are non-specialized; hence, a conclusion can be made, that in common ancestor of Bidentiseta number of dentisetae was reduced to two, but maxillae remained to be non-specialized. Unlike Bidentiseta, in Tridentiseta number of dentisetae is reduced only in the cases when maxilla is strongly specialized as a whole. 

Character of Bidentiseta of unclear phylogenetic status.

(2) Possibly, ventral fibrillose portion on tergalii of Branchitergaliae and a bilamellate structure of tergalii in Furcatergaliae have common origin [see Branchitergaliae (3) and Furcatergaliae (4) below].