Autapomorphies of Rhithrogena/fg1. These are first of all, characters connected with adaptation of larvae to inhabitancy on stone surface in fast streams – further development of scraping specialization of mouth apparatus characteristic for Radulapalpata [see (1) and (2)], loss of ability to respiratory movements [see (6)] and presence of dorsal setae on femora [see (5)]. At the same time, unique apomorphies [see (1)–(3)] undoubtedly testify about holophyly of this taxon.

(1) Maxillary palp is specialized as scraping [in addition to the scraping labial palp – see Radulapalpata (1)] (Kluge 2004: Fig.62:A,D; 64:B,E,H,L): 1^st segment of maxillary palp is thickened; situated inside it muscle-flexor of 2^nd segment is enlarged, fan-form, proximally attached not only to base of segment, but also to its outer side. 2^nd and 3^rd segments are fused to one; apical-ventral side of 2^nd+3^rd segment bears a field of densely and regularly situated small stout curved pectinate scraping setae.

(2) On dorsal side of 2^nd+3^rd segment of labial palp, in the field of irregularly situated setae [see Radulapalpata (1)], the most distal setae, which form a transverse row, are bifurcate (while all other setae are not bifurcate) (Kluge 2004: Fig.62:E–G). Unique apomorphy.

(3) Imaginal and subimaginal lateroparapsidal suture in its posterior part is curved laterally from medioparapsidal suture and reaches area of dorsal attachment of posterior scuto-coxal muscle S.CmP (Kluge 2004: Fig.63). In subimago shape of the lateroparapsidal stripe of lateral pigmented area of mesonotun [see Heptagennota (2)] either repeats the shape of lateroparapsidal suture (Kluge 2004: Fig.63:A,C; 64:D) [see below, Rhithrogena/fg2 (6) and Epeorus/fg1 (7)], or is the same as in other Heptagennota (Kluge 2004: Fig. 64:A) [see below, Plesiomorphies of Paegniodes].

(4) 2^nd+3^rd segment of labial palp [specialized as scraping – see (2) and Radulapalpata (1)] is pointed, thus the field of scraping setae terminates at a distance from the end of the sclerotized ridge (Kluge 2004: Fig.62:G). The same in Kageronia and Ecdyonurus/fg1; probably symplesiomorphy. In Heptagenia/f7=g6 and Cinygma form of this segment is different.

(5) Outer-dorsal margin of larval femur [flattened – see Heptagennota (1)] bears a regular row of long stout setae.

Non-unique apomorphy: similar row of setae occurs in some other rheophilous mayflies. Among Radulapalpata, the same setal row is present in Cinygma; probably synapomorphy; similar row is present in Ecdyonurus/fg1.

(6) Tergalii lost ability to make rhythmical respiratory movements. Non-unique apomorphy (see Index of characters [1.3.30]); among Radulapalpata the same in Cinygma; probably synapomorphy. 

If ventral fibrillose lobe of tergalius [see Branchitergaliae (3)] is well-developed, it is curved in such a manner that passes around the base of tergalius from behind and projects dorsad of it (Kluge 2004: Fig.62:H–I); because of this, when tergalii are spread by sides and pressed to substrate by their ventral (posterior) sides, their fibrillose portions are projected above them and are used for respiration. In this respect Rhithrogena/fg1 differs from Heptagenia/f5=g4, whose tergalii are able to make rhythmical respiratory movements, at rest are directed laterally, flatness of tergalius being perpendicular to longitudinal body axis, and the fibrillose portion of each tergalius locates behind the tergalius (Kluge 2004: Fig.57:C–E). The curvation of fibrillose lobe in Rhithrogena/fg1 testifies that the spread position and immobility of tergalii is secondary (i.e., an apomorphy), while the perpendicular position and mobility of tergalii is a plesiomorphy of Heptagenia/f5=g4 .

(7) Larval caudalii have no whorls of stout setae on hind margins of segments. Among Radulapalpata the same in Cinygma (probably synapomorphy) and Raptoheptagenia, while in Heptagenia/f5=g4 whorls of stout setae are present.

Plesiomorphies of Rhithrogena/fg1. Unlike Cinygma, all 3 maxillary canines are retained (while sometimes being weak). Unlike Heptagenia/f5=g4, abdominal ganglion VIII is not approximated to ganglion VII.