(1) Metathoracic nerve ganglion is strongly transferred anteriorly, nearer to mesothoracic ganglion, being connected with it by a short unpaired connective. Due to this, imaginal and subimaginal median impression of furcasternum [see Heptagennota (4)] is not narrowed in anterior part (unlike all other Heptagennota), but is parallel-sided or widened toward its anterior part, where the metathoracic ganglion is situated (Kluge 2004: Fig.57:A-B).

(2) Mouth apparatus has following unique features.

Left and right mandibles [see Heptagennota (7)] have incisors dissimilar: incisor of left mandible (with mola projected distally) is pointed, with a row of denticles on inner margin; incisor of right mandible (with mola projected proximally) has a large denticle at some distance from apex and a row of smaller denticles proximad of it; denticles on outer margins of both incisors are at a distance from apex (Kluge 2004: Fig.58:B-C); in inversus [Ecdyonurus] the left and right mandibles are changed places (Kluge 1980: Fig.67–68).

Superlingua [curved laterally – see Heptagenia/f5=g4 (1)] has a peculiar shape uniform for all representatives: with a rounded apico-lateral projection (larger than in Heptagenia/f8=g7, more distinct than in Kageronia and Dacnogenia, and smaller than in Stenonema/g1), basally with a small rounded lateral convexity, lateral margin between this convexity and apico-lateral projection is slightly convex (Kluge 2004: Fig.58:D).

On maxilla (Kluge 2004: Fig.58:E-H) the ventral row of setae [see Branchitergaliae (1)] is transformed to a field of irregularly situated setae (unique apomorphy). Proximal dentiseta [see Bidentiseta (1)] is bifurcate.

Vestige of segment 3 of maxillary palp [see Plesiomorphies of Heptagenia/f5=g4] is triangular (Kluge 2004: Fig.56:D-E), larger than in Heptagenia/f6=g5.

Glossae [initially pyramidal – see Radulapalpata (1)] are rhomboid, with convex inner margin and flat apical half, as dorsal edge is approximated to median edge (Kluge 2004: Fig.57:H).

(3) Tergalii are differentiated as following (Kluge 2004: Fig.57:D-E, 58:A): tergalius I is narrowed, with concave anal margin (i.e. has a more or less banana-like shape), that allows it to bend dorsally; tergalii II–VII are widened, with strongly convex anal margin – i.e. have more or less roundish-triangular shape. Unique apomorphy.

(4) Outer (posterior) margin of larval femur [flattened – see Heptagennota (1)] bears a regular row of long stout setae [unlike Heptagenia/f6=g5 – see Kageronia (4) and Heptagenia/f7=g6 (2)]. These setae are situated less dorsally, than similar setae in Rhithrogena/fg1 and Cinygma. Non-unique apomorphy: regular row of setae on outer margin of femur appeared independently in various rheophilous mayflies.

(5) 2^nd+3^rd segment of labial palp [specialized as scraping – see Radulapalpata (1)] is pointed, thus field of scraping setae terminates at a distance from end of sclerotized ridge (Kluge 2004: Fig.57:H). The same in Kageronia and Rhithrogena/fg1; probably symplesiomorphy. In Heptagenia/f7=g6 and Cinygma form of this segment is different.

(6) Tergalius VII [see (3)] nearly always lacks fibrillose lobe [see Branchitergaliae (3)] (thus fibrillose lobe is present only on tergalii I–VII, rarely I–V); only in selected species (particularly in Ecdyonurus/fg2 insignis [H.]) tergalius VII has fibrillose lobe (probably secondarily restored).