(1) Larva is dorsoventrally flattened, with flat sterna; its head is prognathous and forms a head shield; labrum is transverse; legs are enlarged and widely separated, with femora widened and flattened (Kluge 2004: Fig.54:A, 55:A, 58:A). Most representatives inhabit current waters and use this body form to press the body to substrate.

Frons forms more or less expressed head shield, covering mouthparts from above; clypeus is usually membranous and hidden under the head shield, so base of labrum is also hidden under the head shield (Kluge 2004: Fig.65:I). The least expressed is head shield of Pseudiron (Kluge 2004: Fig.52:A) which has carnivorous specialization of mouth apparatus; but here also base of labrum is covered from above by a fold of frons (i.e. head shield) (Kluge 2004: Fig.52:D). Sclerotized clypeus is secondarily developed in some species (particularly, in Epeiron/g1 binerve [Rhithrogena] – Kluge 1987b: Fig.6–7). While in larvae of all Heptagennota head shield is present, imaginal head usually is not modified; but in selected species of Heptagennota face plate of subimago and imago is large, directed anteriorly and more or less repeats shape of larval head shield (some authors regarded this as a generic character, but it evolved repeatedly in various groups inside Heptagennota). Besides Heptagennota, larval head shield independently appeared in some other mayflies (see Index of characters [1.1.4]).

Labrum is usually transverse: width at base much exceeds length, and total width much exceeds width at base. The only exception is made by Cinygma, whose labrum is secondarily narrowed.

Larva lost primary swimming specialization, because its legs, being enlarged and widely separated, are unable to stretch posteriorly and press to the body when larva swims. In different taxa of Heptagennota method of swimming is different: Larva can keep its legs free and shakes them synchronously with abdominal movements, thus translational movement is served both by abdomen and legs (Kluge 2004: Fig.9:D); this is characteristic for Heptagenia/f6=g5. In some non-related taxa (among Ecdyonurus/fg1, Epeorus/fg1 and others) such method of swimming was changed to swimming by legs solely, in this case the primary abdominal dorsoventral swimming movements are lost (Kluge 2004: Fig.9:E); as femora of Heptagennota are flattened, such method of swimming is rather effective. Larvae of Rhithrogena/fg2 have another method of swimming, when primary abdominal movements are retained, but legs are folded and pressed to the body by sides (Kluge 2004: Fig.9:C).

(2) Subimaginal lateral pigmented area of mesonotum posteriorly bifurcates to a lateral portion (occupying antero-lateral part of sublateroscutum and whole lateroscutum) and a lateroparapsidal strip; the lateroparapsidal strip stretches far posteriorly, including into itself lateroparapsidal suture and being laterally limited by a relief line which posteriorly is curved laterally. In the case initial for Heptagennota (in Pseudiron, Arthroplea, Heptagenia/f5=g4 and Cinygma) the lateroparapsidal stripe is widened posteriorly, because lateroparapsidal suture posteriorly diverges with relief line and meets with medioparapsidal suture (Kluge 2004: Fig.52C,54I). In Rhithrogena/fg2 and Epeorus/fg1 lateroparapsidal stripe is curved laterally, because lateroparapsidal suture posteriorly is curved laterally, repeating curvation of the relief line (Kluge 2004: Fig.63:A,C, 64:D). Paegniodes has intermediate structure (Kluge 2004: Fig.64:A).

Probably, the bifurcation of lateral pigmented area and shape of its lateral portion are plesiomorphic (see Index of characters [2.2.14]), while the enlargement of lateroparapsidal stripe and presence of the relief line are unique autapomorphies.

(3) Imaginal and subimaginal anterior paracoxal suture of mesothorax is incomplete (i. e. does not turn to ventral side of episternum and terminates not reaching sternum) and strongly transferred posteriorly toward coxal conjunctiva, because of which katepisternum is reduced to a small piece above coxal conjunctiva and a narrow ridge stretching from this piece by anterior margin of coxal conjunctiva (Kluge 2004: Fig.52:B, 54:J). Besides Heptagennota, paracoxal suture is incomplete in Rallidens and Furcatergaliae only; in most of them it is not transferred posteriorly, but in some of them (for example, Caenoptera) is more or less transferred posteriorly.

(4) Imaginal and subimaginal furcasternal protuberances are separated at least in posterior part (Kluge 2004: Fig.52:B), because metathoracic nerve ganglion is transferred into furcasternum.

Non-unique apomorphy: the same in selected groups of Tridentiseta and Furcatergaliae (see Index of characters [2.2.23]), but not in Eusetisura. In majority of Heptagennota metathoracic nerve ganglion is situated in posterior part of mesothoracic furcasternum, because of this median concavity of furcasternum is widened posteriorly (Kluge 2004: Fig.56:C–D); only in Ecdyonurus/fg1 this ganglion is transferred into anterior part of furcasternum (Kluge 2004: Fig.57:A–B).

(5) Cubital field of fore wing [see Anteritorna (1)] usually with 4 intercalaries forming 2 pairs, among which the posterior pair arise more proximally and is the longest; in each pair the anterior intercalary (nearest to convex CuA) is concave, and the posterior intercalary (nearest to concave CuP) is convex, that serves regular alternating of concave and convex veins in cubital field (Kluge 2004: Fig.53:A,C). Among Heptagennota only one species – Epeiron/g1 binerve [Rhithrogena] – has 2 intercalaries only (Kluge 1987b: Fig.2).

Non-unique apomorphy: this or that number of intercalaries in cubital field evolved independently in different groups of Ephemeroptera (see Index of characters [2.2.52]), and exactly the same two pairs are present in some Metretopus/fg1 (because of this, some authors erroneously placed them to the family Heptageniidae).

In other respects wings of Heptagennota retain normal for Euplectoptera structure and function; only in one undescribed species of Rhithrogena/fg2 from Chukotka Peninsula, fore and hind wings are proportionally diminished and probably unavailable for flight (Kluge 2004: Fig.8:E–F).

(6) Imaginal and subimaginal paracercus is always vestigial. Non-unique apomorphy (see Index of characters [2.3.22]).

(7) Prostheca of initially left mandible (with mola projected distally) is setiform or lost; prostheca of initially right mandible (with mola projected proximally) is always lost (Kluge 2004: Fig.54:E–F, 58:B–C) [in a few representatives left and right mandibles changed places – see below, Arthroplea (2) and Variable characters of Radulapalpata]. Median margin of mandible between kinetodontium and mola often bears more or less long dense setae: they can either be irregular, or form a compact tuft close to prostheca and kinetodontium, or form a regular row along median margin; rarely these setae are absent (in Pseudiron, Cinygma and Bleptus). It is unclear if reduction of prostheca is an autapomorphy of Heptagennota in general, or it is only an autapomorphy of Pentamerotarsata, because in Pseudiron mandibles are strongly specialized and could lost prostheca independently.

(8) Labial palp is 2-segmented; its distal (2^nd+3^rd) segment lacks muscle inside (Kluge 2004: Fig.52:F, 53:E, 57:H, 60:C). Non-unique apomorphy (see Index of characters [1.1.55]). Fusion of 2^nd and 3^rd segments could appear independently in connection with various palp specialization [see below, Pseudiron (1), Arthroplea (1) and Radulapalpata (1)].

Plesiomorphies of Heptagennota. Gonostylus with 2 distal segments (only in Arthroplea and tetramera [Cinygmula] number of segments is secondary increased, but not diminished). Both dentisetae [see Bidentiseta (1)] are always present, being enlarged in Pseudiron (Kluge 2004: Fig.52:E) and vestigial in many Pentamerotarsata (Kluge 2004: Fig.54:M, 58:F–H, 61:H, 65:F). All tergalii I–VII are present (tergalius VII is most greatly reduced in Macdunnoa).

Variable characters of Heptagennota. Imaginal and subimaginal claws of most species are ephemeropteroid; only in selected Tien-Shan–Himalayan species of Cinygmula, Himalogena and Caucasiron on each leg of imago and subimago both claws are pointed, and in selected species of Rhithrogena/fg2 and Epeorus/fg3 on fore legs of male both claws are blunt (but in the last case subimago has all claws ephemeropteroid). Non-unique characters (see Index of characters [2.2.85]).