Hidden flatheaded mayfly (Epeorus abditus) within Epeorus Eaton 1881, subgenus Caucasiron Kluge 1997

NEWS - Hidden flatheaded mayfly (Epeorus abditus) was established as a new species within Epeorus Eaton, 1881, subgenus Caucasiron Kluge, 1997, collected in Türkiye, Georgia and Russia based on several methodological approaches to delimit the new species by analyzing COI sequence data and larval morphology.

The authors describe comparisons with related taxa and diagnostic characters that allow the determination of larvae as part of a detailed study of the Caucasian mayfly fauna, updating the identification keys for other Caucasian species with E. (Caucasiron) abditus, E. hyrcanicus and E. tripertitus.

Epeorus is a diverse genus of mayflies in the Caucasus region. The larvae inhabit cold, well-oxygenated rivers with rocky substrates. Given the body size of the adult larvae which can exceed 20 mm, they represent a charismatic and conspicuous group of mountain aquatic biota.

E. abditus has a relatively wide distribution in the Caucasus region but is relatively rare. Specimens were found in the Pontic Mountains and the Lesser Caucasus (northeastern Turkey and southwestern Georgia), the Greater Caucasus in the central part (Kabardino-Balkaria, Russia) and the eastern part (Kakheti, Georgia).

Larvae were found in small numbers in clear rivers and streams at elevations of 792 and 2192 m on rocky bottom substrates in turbulent flow. They were not recorded in urban and agricultural areas. Larvae coexisted with E. znojkoi, E. alpestris and E. magnus.

The species name abditus means hidden, referring to its rare distribution and morphological similarity to related species. The general color of the larvae is yellowish brown with dark brown spots. The length of the final instar larvae is 13.3 mm (females) and 11.1-11.25 mm (males). The length of the cerci is 1.2× the body length.

The final COI alignment contained 97 sequences, 631 base pairs and 197 parsimony informative positions. E. abditus is delimited as a distinct species. Pairwise genetic distances between the new species and other Caucasiron species range from 8.33% in E. magnus to 15.93% in E. shargi. Genetic distances within E. abditus vary between 0.33 and 1.64%.

E. alpestris can be distinguished from E. abditus by the absence of a postero-lateral projection on tergum X (vs. present in E. abditus). Round macules on the abdominal sterna are always present and the coloration pattern of the abdominal sterna varies from a clear pattern to an indistinct pattern (vs. no pattern).

E. alborzicus has an abdominal sterna with a large circular medial macule and a single or a pair of round macules on tergums II and III (vs. relatively small round medial macules on the abdominal sterna and triangular macules on tergums II and III in E. abditus).

E. bicolliculatus has paired postero-medial processes on abdominal terga II-IX and broadly basally broad setae on terga surfaces (vs. narrowly basally broad setae in E. abditus). E. magnus has dense, bristle-like setae on the dorsal surface of the labrum (vs. sparse, hair-like setae in E. abditus) and often has a well-developed lateral process on tergum X (vs. only short process in E. abditus).

E. soldani has broadly basally broad setae on abdominal terga (vs. narrowly broad in E. abditus). E. sinitshenkovae has poorly developed projections on the costal margin of the gill plates (vs. well-developed projections in E. abditus).

All other Caucasiron species from the Caucasus, Mediterranean, and Irano-Anatolian regions can be distinguished from E. abditus by the presence of specific color patterns on the abdominal sterna and/or the presence of femoral spots. These include E. caucasicus, E. nigripilosus, E. zagrosicus, E. iranicus, E. longimaculatus, E. turcicus, E. shargi, E. hyrcanicus and E. tripertitus.

Original research

Hrivniak Ľ, Sroka P, Türkmen G, Martynov AV, Bojková J (2024). Integrative delimitation of a new Epeorus (Caucasiron) (Ephemeroptera, Heptageniidae) from the Caucasus with a supplement to the identification guide of Caucasian and Irano-Anatolian species. ZooKeys 1214: 265-279, DOI:10.3897/zookeys.1214.131266

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