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The first representative of the subgenus Helvetoraeticus Bauernfeind & Soldán, 2012, from the Caucasus Mountains, Ecdyonurus (Helvetoraeticus) adjaricus sp. nov., is described on the basis of larvae, female imago (reared from larva) and male imago from the Autonomous Republic of Adjara, Georgia. The male imago of the new species can be separated from other representatives of Helvetoraeticus by its conspicuous yellowish wings coloration (especially of hind wings) and the shape of the penis lobes. The larva has a distinctive broad and apically pointed lateral projection on the pronotum, pointed bristles on the ventral side of the posterior border of the femora and markedly long, sharp posterolateral expansions of abdominal sterna. This last character is unique within Helvetoraeticus. The new species is most closely related to E. krueperi (Stein, 1863).

This study is focussed on the redescription of Ecdyonurus (Ecdyonurus) russevi Braasch & Soldan on the basis of the type material (holotype and paratypes) and topotypes collected in the Strandzha Mts. (Bulgaria). Female imago and subimago, larva and egg of the species are described for the first time and the male imago is redescribed in detail. The features distinguishing the species from other representatives of the genus Ecdyonurus are presented. Ecdyonurus russevi differs by the combination of several characters in the colour pattern of abdominal terga and wings, colour of lateral portion of male eyes and male genitalia structure in adults; some overlap has been observed in the number of groups of setae, bristles and hair-like setae on maxillae and labial palps, shape of pronotal projection and colour of tarsi in larvae; and insignificant number of knob-terminated coiled threads on exochorion, with only a few such attachment elements on one pole in eggs. Biology and present distribution of the species are discussed.

The species Ecdyonurus sumatranus Ulmer, 1939 was described from Sumatra based on a female imago and a single nymph. It was designated as the type-species of the genus Ecdyonuroides Dang, 1967, erected because of the peculiar morphology of the nymph. This genus was put into synonymy later and the species is currently known as Thalerosphyrus sumatranus (Ulmer, 1939). The female imago holotype of Ecdyonurus sumatranus Ulmer, 1939 is reinvestigated and revealed to belong to the genus Rhithrogena Eaton, 1881. The combination Rhithrogena sumatrana (Ulmer, 1939) comb. nov. is thus proposed. The nymphs described by Ulmer (1939) from Java sub. nom. Rhithrogena parva (?) are associated to this species, and are redescribed with new material coming from Java and Lombok. Rhithrogena parva (Ulmer, 1912) is redescribed based on the syntype series from Taiwan and male genitalia are illustrated for the first time. Supplementary description is provided for the nymph of Rh. parva and for the one of Rh. ampla Kang & Yang, 1994, also from Taiwan. The status of the subgenus Tumungula Zhou & Peters, 2004 is briefly discussed. The nymph associated by Ulmer (1939) to Ecdyonurus sumatranus is renamed Thalerosphyrus lamuriensis sp. nov. The genus Ecdyonuroides Dang, 1967 is considered as a synonym of Rhithrogena syn. nov.

Ecdyonurus dispar gratificus ssp. nov. is reported from several small streams and rivers within the Donetsk Ridge (East of Ukraine). The new subspecies is described and illustrated on larvae and reared adults of both sexes. SEM photographs of the egg structures are presented. Critical diagnostic characters distinguishing the new subspecies from other representatives of the subgenus Ecdyonurus Eaton, 1868 and especially from the nominal subspecies are discussed. The data on the biology and distribution are presented.