CLADOENDESIS OF EPHEMEROPTERA

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(1) Mouth apparatus, retaining the scraping specialization of labial and maxillary palps [see Radulapalpata (1) and Rhithrogena/fg1 (1)], has a peculiar biting specialization, which is expressed in modification of maxillae and mandibles.

Maxilla [see Radulapalpata (3)] is shortened, inclined, with acute apical-median margin [but ventral row of setae is straight and goes parallel to median margin – see Epeorus/fg1 (6)]. Apical margin of maxilla is bare, vestiges of pectinate setae [see Epeorus/fg1 (5)] and hairs are completely lost. All 3 maxillary canines are very massive, strongly sclerotized; at the same time canines are not pressed together, and both dentisetae [see Bidentiseta (1)] are not thickened (Kluge 2004: Fig.65:F) (unlike Nesameletus/f2=Metamonius/g2 and some Turbanoculata, whose maxillary canines are also thickened).

Mandible is shorter (in relation to perpendicular to axis of articulation) and more stout, than in other Pentamerotarsata, incisor and kinetodontium are stout; median margin is short, its setae and setiform prostheca form a compact tuft close to kinetodontium [see Heptagennota (7)] (Eaton 1883–1888: Pl.55–56). Mandibles with similar proportions but of somewhat different shape occur in selected carnivorous species of Heptagenia/f7=g6 and Himalogena.

(2) On tergalii II–VII apical part of costal rib is covered by long slender soft hairs; they form a common band with curved spin-like setae, which cover more proximal part of the costal rib [see Epeorus/fg2 (2)] (Kluge 2004: Fig.65:C-E,G-H) (unlike Ironodes, whose apex of costal rib is glabrous).

(3) Superlinguae are widest at middle part, convergent and narrowed toward apex. The same in Rhithrogena/fg2, unlike Ironodes and Bleptus [for comment – see Ironodes (3) above].

(4) Larval abdominal segments can have more or less prominent projections close to tergalial articulatory membranes: besides a small rounded projection ventrad of the tergalius base (corresponding to posterolateral spine of many mayflies), there can be developed a larger supratergalial projection just dorsad of the tergalius base. Supratergalial projection is flat, can be either small and rounded (in Iron/fg1, some Proepeorus and some Epeorus/fg4), or long, pointed and curved postero-medially (in Belovius/fg1, some Proepeorus and some Epeorus/fg4).

Plesiomorphy of Epeorus/fg3. Each tergalius I–VII retains fibrillose lobe [see Branchitergaliae (3)] (unlike Ironodes).