CLADOENDESIS OF EPHEMEROPTERA

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(1) Tergalius I is more or less widened anteriad of costal rib, thus the costal rib passes at a distance from margin (unlike Bleptus, where all tergalii ribs are marginal).

(2) On tergalii II–VII strongly developed costal rib (which, unlike tergalius I, retains its position on costal margin) is covered by dense short stout curved pointed spine-like setae (Kluge 2004: Fig.64:J). Probably, this helps larva to couple with stone, on which larva sits in a stream: tergalii are immovably spread by sides and pressed by their costal margins to the substrate. Such specialization of tergalii appeared to be possible, because tergalii are unable to respiratory movements [see Rhithrogena/fg1 (6)].

(3) Dorsal side of larval body bears stripes of dense thin hairs: anterior margin of head shield [see Heptagennota (1)] is widened and bears a stripe of very dense thin hairs directed anteriorly or dorsally; dorsal side of each tibia bears a longitudinal stripe of dense thin hairs directed dorsally.

Similar stripes of dorsally directed hairs on various parts of body (legs, head, caudalii, abdomen) evolved in various mayfly groups where larvae are specialized for inhabitancy in rapid streams. Probably these hairs have some hydrodynamic importance. In other Radulapalpata such hairs are not developed or weakly developed. Judging by uniform structure and position of hairs on head and tibiae of Epeorus/fg2, in this taxon these hairs have common origin (i.e. represent an autapomorphy of Epeorus/fg2). Besides this, dorsal stripes of hairs on other parts of body (cerci, abdomen) evolved independently in selected groups of Epeorus/fg3.

Plesiomorphy of Epeorus/fg2. Unlike Bleptus, glossae are pyramidal [see Radulapalpata (1)] (Kluge 2004: Fig.64:I).