CLADOENDESIS OF EPHEMEROPTERA

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(1) Winged stages are short-living: Legs are non-functional (except for fore legs of male). Moult from subimago to imago takes place in males only. Pterothorax is modified, mesonotal suture is extremely stretched posteriorly up to disappearance; subimaginal cuticle lost pigmentation [see Fimbriatotergaliae (2)]. Non-unique apomorphies (see Index of characters [2], [2.2.8] and [2.2.14]); among Cryptoprosternata, the same in Polymitarcys/f1=Ephoron/g2.

(2) Wings with gemination: on fore wing apices of veins are brought together in pairs RSa₂+iRS, RSp+MA₁, iMA+MA₂; main longitudinal veins are firm, membrane and crossveins are soft (Kluge 2004: Fig.75:A–B; Eaton 1883–1888: Pl.1–2; Demoulin 1965b: Fig.1–8). Non-unique apomorphy (see Index of characters [2.2.28]): similar vein pairs are present in Behningia/fg3 and some female Euthyplocia/fg1; in Discoglossata veins are united in pairs in another manner.

(3) In male subimago fore leg [short – see Palingenia/f2=g1 (7)] is shortened and thickened in a special manner: tibia is thick; tarsus is short, thick and conically narrowed apically.

In male imago of Palingenia/f4=g3 tarsus has normal form – long and non-conic (Demoulin 1965b: Fig.1–2); in male imago of Anagenesia/g1 tarsus has the same form as in subimago (ibid., Fig.3–8).

(4) In female [non-moulting – see (1)] fore leg is vestigial, with a single blunt claw, sometimes with blunt vestige of second claw [in male imago and subimago fore leg has two blunt claws – see Palingenia/f2=g1 (7)]; on middle and hind legs claws can be either ephemeropteroid [see below, Plesiomorphies of Palingenia/f4=g3], or vestigial [see below, Anagenesia/g1 (2)].

Some species have sexual dimorphism in shape of larval claws [lacking denticles – see Plesiomorphies of Fimbriatotergaliae], which is connected with strong reduction of adult claws in female: claws of all legs of male mature larva can be swollen in proximal part, inside which adult claw develops, while claws of female mature larva and young larvae of both sexes are entirely thin (Soldan 1981). In other mayflies larval claws have no sexual dimorphism, independently of sexual dimorphism in adults (mature larvae of Pentagenia were not examined).

(5) Gonostyli have peculiar structure. 1^st segment is not separated by suture from second; inner side of gonostylus has a more or less expressed projection near base (possibly corresponding to apex of strongly shortened 1^st segment). Usually 2 distal segments are present, but tendency to increasing of their number exists (Table): Anagenesia/g2 paradoxa [A.] has 3–4 distal segments, Palingenia/f4=g3 and Mortogenesia have 4–6 distal segments; selected specimens have 1 distal segment.

(6) Imaginal and subimaginal paracercus is vestigial not only in male [see Cryptoprosternata (5)], but in female as well. Non-unique apomorphy (see Index of characters [2.3.22]).

(7) Egg has a form of biconvex round lens; thread-like anchors are absent; at least in some representatives egg can be attached to substrate by a thin lamella which covers egg surface (Kosova 1967: Fig.1–2; Landolt & al. 1995: Fig.11–14). Egg of Pentagenia has the same kind of anchor, but egg form is irregular with convexity. Lens-like eggs are found in Palingenia/f4=g3, Anagenesia/g2, Chankagenesia and Cheirogenesia. Non-unique apomorphy: the same in Prionoides; ovoid (but not round) lens-like eggs occurs also in some Ameletus/fg2.