(Panephemeroptera Euephemeroptera Euplectoptera Anteritorna Bidentiseta Branchitergaliae
Heptagennota Pentamerotarsata Radulapalpata 
Epeorus/fg1Rhithrogena/fg2 - Rhithrogena/fg3)

Nomen hierarchicum: Rhithrogena/fg3 [f:1917; g:1881] (sine Cinygmula; incl. Epeiron, Himalogena, Sibirigena)

In circumscription fits:

— subgen. Rhithrogena: Kluge 1983b: 16 (unpublished); 1988: 306

— gen. Rhithrogena Eaton 1881: 23

— Rhithrogena/fg3: Kluge 2004: 193

References. Eaton 1883–1888: *; – Lestage 1917: *; – Needham & Traver & Hsu 1935: *; – Strenger 1953: '; – Edmunds & Jensen & Berner 1976: *; – Tshernova 1976: *; – Kluge 1988: *; – 1993: *; – 2004: * * *.

Autapomorphies of Rhithrogena/fg3.

(1) On 2nd+3rd segment of maxillary palp field of scraping setae [see Rhithrogena/fg1 (1) and Rhithrogena/fg2 (2)] occupies nearly whole length of the segment; denticles of these setae are enlarged (Strenger 1953: Fig.11–12). Unique apomorphy: in all other Rhithrogena/fg1 scraping specialization is not so strongly expressed, and scraping setae occupy a distal part of the segment only.

(2) Patella-tibial suture (initially present on middle and hind legs only) is equally developed on all legs of larva; this character is not due to winged stages, in which difference between fore tibia and other tibiae can be retained. The same in Anteropatellata only (see Index of characters [1.2.18]).

(3) Tergalii are highly specialized, forming an adhesive sucking disc of following structure (Kluge 2004: Fig.62:C,H–O):

Tergalius I is strongly widened in such a manner that projects far anteriorly and greatly widened in front of costal rib. These anterior projections of left and right tergalii I are contiguous or closely brought together on ventral side, under thorax. Exactly anteriad of the place of tergalii attachment, ventral side of abdominal segment I has a pair of plates projected anteriorly; into a chink between this plate and sternum, a proximalmost part of anterior margin of tergalius is inputted.

Tergalii II–VI are wide, thus, being directed laterally, overlap one another by their margins.

Tergalius VII has a longitudinal fold, because of which, being directed posterior-medially, is bent under posterior end of abdomen.

Ventral fibrillose lobes of all tergalii [see Branchitergaliae (3)] are well-developed and bent to dorsal side, projecting above tergalii. Because of their shape, all tergalii I–VII together form a united sucking disc. This specialization of tergalii appeared to be possible, because tergalii are unable to respiratory movements [see Rhithrogena/fg1 (6)].

On each tergalius costal rib goes at a distance from anterior margin and does not reach tergalius margin; so tergalii margins are thin and soft. This allows larva to adhere by sucking to a smooth stone surface for a short time so effectively, that if try to take it off, it can be only moved by stone surface but not detached (unlike Epeorus/fg3-Iron/g1, whose sucking disc can have the same shape, but is bordered by ribs and is not so effective). Many species of Rhithrogena/fg3 prefer to inhabit on small roundish stones with very smooth surface. Tergalius margin can be integral or incised; in all species with incised tergalii, incisions have the same form: they divide outer tergalius margin into numerous festoon-like semicircular lobes. In various species such incisions are present either on all tergalii I–VII, or on tergalii I and VII only, or on tergalius I only, or absent.

Independently from Rhithrogena/fg3, similar sucking disc appeared in some groups of Epeorus/fg3-Iron/g1 and in some Australian Leptophlebia/fg1. In some of them outlines of whole disc and of each tergalius are the same as in Rhithrogena/fg3; in Epeorus/fg3, as well as in Rhithrogena/fg3, fibrillose portions are curved up. But the structure of first abdominal sternum and the position of costal rib of tergalii II–VI are unique characters of Rhithrogena/fg3.

(4) Subimaginal lateroparapsidal stripe of pigmented area of mesonotum [non-contiguous with medioparapsidal suture – see Rhithrogena/fg2 (6)] is continued behind apex of lateroparapsidal suture; thus behind apex of lateroparapsidal suture (which as in other mayflies represents a groove-like concavity) there is present a non-concave pigmented portion whose length and width slightly exceed width of lateroparapsidal suture; often (but not always) this portion is pigmented more intensively than the whole lateroparapsidal stripe; this portion lies on posterior scutal protuberance of mesonotum, while lateroparapsidal suture terminates at anterior margin of this protuberance (Kluge 2004: Fig.63:C). Unique apomorphy: unlike Rhithrogena/fg3, in Cinygmula and Epeorus/fg1 lateroparapsidal suture reaches or nearly reaches apex of lateroparapsidal pigmented stripe, so there is no such marked non-concave pigmented area behind it (Kluge 2004: Fig.63:A).

(5) Imaginal penis lacks median titillators [see Pentamerotarsata (5)]; usually it has a pair of ventral titillators [see Rhithrogena/fg2 (4)], sometimes ventral titillators are also absent [see below, Epeiron/g1 (3) and Sibirigena (3)]. Non-unique apomorphy (see Index of characters [2.3.15]).

Plesiomorphy of Rhithrogena/fg3. Larval caudalii always retain vestigial primary swimming setae [see Pentamerotarsata (6)] at least in distal part (unlike Cinygmula and some others – see Index of characters [1.3.66]).

Size. Fore wing length 5–17 mm.

Distribution. Holarctic and Oriental Region.

The taxon Rhithrogena/fg3 is divided into:

1. Rhithrogena/fg4

2. Himalogena

3. Sibirigena

4. Epeiron/g1

4.1. Epeiron/g2

4.2. Tumungula

Some species have uncertain systematic position