Identification guide to larvae of Caucasian Epeorus (Caucasiron) (Ephemeroptera, Heptageniidae)

Abstract The Caucasus and adjacent areas are inhabited by fifteen species of mayflies of the genus Epeorus, subgenus Caucasiron Kluge, 1997 (Heptageniidae). This identification guide aims to facilitate an accurate species identification of their larvae and sum up all available information on their taxonomy and distribution. An identification key is provided, and the important diagnostic characters of all species are described and illustrated. The larva of E. (C.) insularis (Braasch, 1983) is described for the first time. This study enables the routine identification of Caucasiron larvae necessary for biomonitoring and hydrobiological research in the Caucasus region.


Introduction
The knowledge facilitating the identification of mayflies inhabiting the Caucasus biodiversity hotspot (Myers et al. 2000) is limited to checklists (e.g., Bojková et al. 2018: Iran;Gabelashvili et al. 2018: Georgia;Hrivniak et al. 2018: Armenia) and alpha taxonomic papers focused mostly on the delimitation of newly described species/taxa. The available identification keys deal with selected genera only (Sinitshenkova 1976: Epeorus Eaton, 1881and Rhithrogena Eaton, 1882Jacob andZimmerman 1978: Baetis Leach, 1815) or mayfly fauna of the wider region without sufficient information on Caucasian species specifically (Kluge 1997a). These keys are largely outdated, because the number of species newly described from the Caucasus has been steadily increasing in recent years (e.g., Hrivniak et al. 2017;2019;2020a;Martynov and Godunko 2017;Bojková et al. 2018). Therefore, the identification of larvae to the species level is complicated due to the necessity of compiling information from original descriptions and requires advanced experience with the taxonomy of mayflies and comparative collections. Modern identification keys are needed especially for researchers implementing biomonitoring programmes and routine hydrobiological surveys in the region. They often use data on the generic or family level only (e.g., Hakobyan et al. 2010;Asatryan et al. 2016;Hovhannisyan and Shahnazaryan 2016;Sharifinia et al. 2016) and often include numerous misidentifications (cf. Bojková et al. 2018). This study aims to partly fill this gap by providing a complex identification guide for the larvae of the genus Epeorus, subgenus Caucasiron Kluge, 1997 (Heptageniidae) (herineafter Caucasiron) occurring in the Caucasus and adjacent areas. The Epeorus s. l. larvae are known to be sensitive to pollution, are relatively stenotopic, restricted to lotic habitats, and form an ecologically important component in macroinvertebrate assemblages (Morisi et al. 2003). Caucasiron species, together with the remaining representatives of Heptageniidae, can, therefore, be used as indicators in water quality assessments and hydrobiological surveys in the Caucasus region.
Caucasiron ranks among the most diverse mayfly groups in the Caucasus region, together with the genera Rhithrogena, Electrogena Zurwerra &Tomka, 1985, andEcdyonurus Eaton, 1868. It is a monophyletic subgenus, sister to the subgenus Iron Eaton, 1885 distributed in North, Central and East Asia and the Nearctic Region (Hrivniak et al. 2020b). Kluge (1997b) defined Caucasiron based on the unique apomorphy among Heptageniidae (and mayflies in general), a projection on the costal margin of the gill plates II-VII (see Fig. 5G, arrow). Other morphological characters of Caucasiron include: gill plates forming a "suction disc" (i.e., a structure consisting of enlarged gill plate I and overlapping gill plates II-VII, and gill plate VII with a longitudinal fold allowing it to be bent ventrally under the abdominal segments; Fig. 1B-D) and medio-dorsally directed hair-like setae along the anterior margin of the head (Kluge 2015: 346, fig. 178). Imagines are characterized by tubular penis lobes without dorso-lateral denticles and well developed median titillators (Fig. 1A). For the morphological comparison of Caucasiron with other related subgenera of the genus Epeorus s. l. see Braasch (2006;Alpiron Braasch, 2006, Ironopsis Traver, 1935 and Kluge (2004;Iron).
The global diversity of Caucasiron comprises 17 species (Hrivniak et al. 2020b). This identification guide deals with 14 species inhabiting the Caucasus and neighbouring mountain ranges, such as the Zagros and Taurus Mountains, and one species inhabiting Samos Island. The extralimital species E. (C.) guttatus (Braasch, 1979) from Central Asia, E. (C.) extraordinarius Chen et al., 2010 from south-western China, and other Central Asian species presumably belonging to the genus Caucasiron (Hrivniak et al. 2017) are not included. All 15 species included in the guide are easily distinguishable based on both morphology and molecular data (Hrivniak et al. 2017(Hrivniak et al. , 2019(Hrivniak et al. , 2020a. Additionally, Hrivniak et al. (2020b) identified seven other distinct lineages based on molecular data only. Most of these lineages likely represent cryptic species or as yet have no formal morphological description. The distribution of possible cryptic lineages is to be found in the guide remarks of the respective morphotypes.
Individual species of Caucasiron have different distribution patterns in the Caucasus. Some species are local endemics to the Greater Caucasus, Pontic, Zagros, or Alborz Mountains. Others are widely distributed throughout the Caucasus and the adjacent areas of Anatolia, Cyprus, Iran, and Iraq (Hrivniak et al. 2017(Hrivniak et al. , 2019(Hrivniak et al. , 2020a. Their distribution and diversity patterns can be explained by geological and climatic history, and land development in the region that have significantly affected the diversification of Caucasiron in the Caucasus (Hrivniak et al. 2020b).
We aim to provide information necessary for the accurate species identification of Caucasiron to the professional public in order to allow the integration of Caucasiron into the hydrobiological surveys and biodiversity monitoring in the Caucasus. The main objectives of this study are to (i) form an identification key based on the reliable morphological characters of larvae, (ii) make an inventory of records of all species, and (iii) describe their geographic and altitudinal distribution based on our extensive data and available literature data. Caucasiron imagines are not described because of the lack of unambiguously associated specimens. Only information about whether the subimagines or imagines of a given species are described, how they were associated, and who described them, is provided.

Sampling
Larvae of Caucasiron were collected at 293 localities in Turkey, Georgia, Russia, Armenia, Azerbaijan, Iran, and Samos and Cyprus in 2008-2019 (Fig. 2). They were sampled by a hand net or a metal strainer and fixed in 96% ethanol in the field. Sampling sites fully covered Caucasus region and the geographical distribution of all known Caucasian Caucasiron species.
Body parts with morphological structures requiring microscopical examination (i.e., mouthparts, femora, abdominal terga) were mounted on slide using HydroMatrix® (Mi-croTech Lab, Graz, Austria) mounting medium. In order to remove the muscle tissue for an investigation of the cuticular structure, the specimens were left overnight in a 10% solution of NaOH prior to slide mounting. Drawings were made using a stereomicroscope Olympus SZX7 and a microscope Olympus BX41, both equipped with a drawing attachment. Photographs were obtained using Leica DFC450 camera fitted with macroscope Leica Z16 APO and folded in Helicon Focus version 5.3. All photographs were subsequently enhanced with Adobe Photoshop™ CS5. The terminology was used mostly according to Kluge and Novikova (2011) and Kluge (2004Kluge ( , 2015.

Larval morphological diagnostic characters
A set of larval diagnostic characters used in the identification guide (listed below) was derived from Braasch and Soldán (1979), who proposed them for the distinguishing larvae of the genus Iron. In the concept of Braasch and Soldán (1979), Iron included currently recognized taxa Iron, Ironopsis, Caucasiron, and Alpiron (see Hrivniak et al. 2020b for the revised concept and phylogeny of these taxa). Individual diagnostic characters are briefly described and figured for all species.
Morphological characters for the larval identification of Caucasiron: i) coloration of abdominal terga: shape of medial macula (Fig. 4I, arrow) and length of lateral stripes (extended dorso-posteriorly or not; Figs 13H, I, 16G respectively). Sometimes the medial macula is visible only partly being concealed by a preceding abdominal segment due to the telescoping contraction of the abdomen. The abdomen must be sufficiently extended manually to expose all length of individual segments to recognize the shape of the medial macula. ii) coloration of abdominal sterna: presence/absence and shape of pattern.
The coloration pattern of abdominal terga and/or sterna is often species-specific and valuable in the species identification of Caucasiron larvae. It is easily visible and, thus, valuable for the routine identification. However, it often fades in older material or in inadequately fixed larvae, and the intensity of coloration, especially of abdominal sterna, varies among specimens and instars, and may be poorly expressed in some specimens. Therefore, the combination of all characters provided in the guide should be considered for an accurate species identification. The coloration pattern is usually present on terga II-IX (X) and sterna II-VIII (IX). However, patterns vary among segments, therefore, for the purpose of the key we compare terga V-VII and sterna II-VI, which are more species-specific. iii) surface of abdominal terga: presence/absence of outgrowths (protuberances, spines, etc.), shape of sensory setae (hair-like/wide at base; Figs 5E, 20E respectively), density, shape, and sclerotization of denticles along posterior margin of tergum VII (mounting on microscopic slide required). Except E. (C.) bicolliculatus with a pair of postero-medial protuberances on abdominal terga II-IX (Hrivniak et al. 2017: figs 11, 31, 32;Fig. 34H, arrows), dorsal surface of abdominal terga of Caucasian Caucasiron species do not bear any outgrowths or spines. Denticles along posterior margin of abdominal terga are pointed and irregular in size in all Caucasian Caucasiron species. However, the denticles of some species are denser and more sclerotized, e.g., in E. (C.) znojkoi Tshernova, 1938 (Fig. 8E) and E. (C.) nigripilosus (Sinitshenkova, 1976) (Fig. 14E), strongly sclerotized, elongated and curved, e.g., in E. (C.) magnus (Fig. 11E) or less sclerotized and narrowed, e.g., in E. (C.) longimaculatus (Fig. 29E). The pattern of denticles slightly varies among terga and depends on a lateral distance from the midline of a given tergum. Thus, the reference part for the description of denticulation along the posterior margin of terga is used in the key. It is represented by tergum VII, the section from its midline to approximately half distance to the lateral margin. iv) medial hypodermal femur spots: presence/absence and shape (rounded/elongated). The character is relatively stable and usually present on dorsal surface of femora of all leg pairs. Variability was observed in E. (C.) caucasicus ( Fig. 4F-H) and includes absence on all or at least some of the legs. v) mouthparts: setation on dorsal surface of labrum (sparse hair-like setae/dense bristle-like setae; Figs 5A, 11A respectively) and shape of mandibular incisors (blunt/ pointed) (mounting on microscopic slide required). Mouthparts of Caucasian Caucasiron species are generally without distinct diagnostic characters in most of the species. The only exception is labrum, mandibles and maxillae of E. (C.) magnus. This species differs from all others by setation of dorsal surface of labrum (dense bristle-like setae; Fig. 11A), pointed mandibular incisors (Fig. 11B, C), and thickened maxillary dentisetae (not figured). The shape of labrum is generally variable in most of the Caucasian Caucasiron. Exceptions are E. (C.) magnus, E. (C.) alpestris, and E. (C.) sinitshenkovae, the shape of labrum of which can be considered as one of the diagnostic characters. However, it should be noted that the shape of labrum is often distorted during the slide preparation and should be observed in natural position (not flattened), as well as suggested for other Heptageniidae (e.g., Ecdyonurus) (Bauernfeind 1997). Therefore, the shape of labra figured in the guide are not flattened on slide but drawn from dorsal view in natural position. Drawings of the shape of mandibular incisors were based on flattened incisors on slides. Despite mandibular incisors are not considered as distinct character in the species identification, they are figured in the guide for comparison with E. (C.) magnus, and for purposes of further taxonomy, in case some new species with different incisors will be found in the future. vi) gill plates: size of a projection on costal margin of gill plates III (with/without distinct projection; Fig. 5G, arrow and Fig. 29G respectively) and shape of gill plates VII in natural position from ventral view (narrow/wide). The shape of gill plates I-VI is more or less identical between individual species. However, the gill plate VII is specific for some species; e.g., narrow, banana-shaped plate in E. Importantly, the shape of the gill plate VII must be observed in natural position from ventral view, without flattening on a slide (as shown e.g., in Fig. 7L-P). As a part of the gill plate VII is longitudinally bent under the abdomen (Fig. 1C, D), its shape is often deformed during the slide preparation by straightening of its inner margin. vii) tarsal claw denticulation: number of denticles.
Denticulation of tarsal claws was omitted in the guide, due to its high overlap among species and frequent abrasion. Tarsal claws of all species usually possess 2-4 denticles. viii) shape of head in fully grown larvae: ellipsoid/oval trapezoidal/sharply trapezoidal.
The shape of head (in dorsal view) may be used as one of the diagnostic characters in some species; e.g., E. (C.) znojkoi is characteristic by a distinctly angular, sharply trapezoidal head (Fig. 7D), E. (C.) magnus and E. (C.) shargi by more oval trapezoidal head with more broadly rounded corners (Fig. 10D, E and Fig. 43D respectively), and E. (C.) longimaculatus by more or less rounded, ellipsoid shape of head (Fig. 28D). Interspecific differences in the shape of head are most distinct in fully grown or late instars of males (and females in E. (C.) magnus). ix) postero-lateral projection on tergum X: presence/absence ( Fig. 11K-M, arrows and 17L respectively) and its size.
We also figure a shape of medial emargination of female sternum IX and spatulate setae on dorsal surface of femora (figures in the guide include the variability from proximal to distal margin of femora of all leg pairs). Despite a relatively wide range of variability in these characters, it may be helpful in identification of some species.

Identification guide to larvae of Caucasian species of Caucasiron
How to use the guide?
The dichotomous key divides Caucasiron species into two morphological groups, further divided into subgroups. They do not correspond with the phylogeny and merely represent groupings defined for the practical purpose of species identification. Some characters within the key are subject to variation in some species. For instance, E. (C.) caucasicus usually has a median hypodermal femur spot, but in rare instances it is absent. We deal with this ambiguity by placing such species both in Group A (femur spot present) and B (femur spot absent). Thus, there are sometimes multiple paths leading to the same species in the key.
Most Caucasiron species are defined on the basis of a particular combination of several morphological characters. Following species identification using the dichotomous key, it is recommended to compare all the remaining diagnostic characters for a given species, provided in detail in the "Main morphological diagnostic characters of larvae" for each species. Variability of morphological diagnostic characters is described in the remarks section.
The "Main morphological diagnostic characters of larvae" were described based on late-instar larvae (fully-grown larvae). The order of characters is not concise in relation to all species; it always starts with the most prominent character for a given species after which the value of subsequent characters for species identification diminishes. For each species included in the guide, geographical and altitudinal distribution with frequency of sampling sites is provided. The construction of distribution maps was based on published records (Table 1) and our unpublished data. Brief information on distribution Table 1. Records of Caucasiron species from the Caucasus and adjacent areas. Abbreviations used: A-Armenia; N-Nakhchivan; Te-eastern Turkey; T-Turkey*; G-Georgia; AZ-Azerbadijan; I-Iran; Iq-Iraq; Is-Israel; S-Syria; Rw-Russia (western Caucasus); Rc-Russia (central Caucasus); Sa-Samos Island; C-Cyprus Island.
Remarks Taxonomy. This species was described based on male imagines from the Nakchivan Autonomous Republic (upper Sakarsu River) (Tshernova 1938). The type series is deposited in the Institute of Zoology, Russian Academy of Sciences, Saint Petersburg (IZ) (Kluge 1995). Female imago not described; the larva described by Sinitshenkova (1976) from several localities in Russia, Armenia, and Azerbaijan. Larvae and imagines were associated based on the same sampling sites (a part of the larval material originated from the vicinity of the type locality) and a similarity in the coloration of abdomen of the larva and imagines. The description and validity of larval diagnostic characters were discussed by Braasch (1979Braasch ( , 1980. According to him, Sinitshenkova (1976) described the larva of E. (C.) znojkoi under the name E. (C.) caucasicus by mistake. This opinion was supported by the investigation of imagines reared from larvae corresponding to E. (C.) caucasicus described by Sinitshenkova (1976). Imagines corresponded to E. (C.) znojkoi as were described by Tshernova (1938). The larva belonging to E. (C.) caucasicus was also described in Sinitshenkova (1976), but under erroneous attribution to newly proposed species E. (C.) fuscus. Later, E. (C.) fuscus was considered as a synonym of E. (C.) caucasicus (Braasch 1979;Braasch and Soldán 1979).
Habitat. Larvae inhabit streams and rivers of various sizes, from larger braided low altitude rivers to small streams at high altitude. Altitudinal range of sampling sites -6-2453 m a.s.l. (Fig. 6). Most frequently found in low and middle altitudes. Often syntopic with E. (C.) magnus.
Remarks. Morphology. The reduction of reddish coloration of abdominal sterna observed particularly in specimens collected from Turkey (Fig. 7N) and northern Iran (Fig. 7O, P). Similar coloration pattern of sterna as present in E. (C.) insularis (Fig. 31J).
Taxonomy. This species was described based on male and female subimagines and imagines from the Nakchivan Autonomous Republic (Tshernova 1938). The type series is deposited in IZ (Kluge 1995). The larva was described by Sinitshenkova (1976) based on material collected in Georgia, Russia (the central Greater Caucasus), Armenia and the type locality. Larvae were identified as species znojkoi, based on the proximity of its type locality and the similarity of markings on abdominal terga. However, the description of larva is confusing, because the larva of E. (C.) znojkoi was erroneously described under the name E. (C.) caucasicus by Sinitshenkova (1976) (Braasch, 1980). Therefore, the larva described by Sinitshenkova (1976) as E. (C.) znojkoi should belong to a different species. Its diagnostic characters correspond to those of E. (C.) magnus that was later described by Braasch (1978). These characters include: (i) body length: Tshernova (1938) noted 9.5-12 mm for imagines of species E. (C.) znojkoi; contrary to Sinitshenkova (1976) who noted 14-19 mm for the larvae. Larvae of species magnus exhibit 20-24 mm as described by Braasch (1978); (ii) shape of head: trapezoidal head with rounded edges as figured by Sinitshenkova (1976) is typical for E. (C.) magnus (Fig. 10D, E), not to E. (C.) znojkoi with more angular edges of head (Fig. 7D); (iii) setation of labrum: the shape of labrum and dense setae on its dorsal surface as figured by Sinitshenkova (1976) is characteristic for E. (C.) magnus (Fig. 11A); (iv) coloration of abdominal sterna: an absence of coloration on abdominal sterna as described by Sinitshenkova (1976)
Distribution. Georgia, south-western Russia, Azerbaijan, Armenia, Turkey (Fig. 9). One of the most widespread species in the Caucasus.
Habitat. Larvae inhabit streams and rivers of various sizes, from larger braided low-altitude rivers to small streams at high altitude. Altitudinal range of sampling sites 6-2474 m a.s.l. (Fig. 9). Most frequently found at low and middle altitude. Often syntopic with E. (C.) znojkoi.
Taxonomy. Original description based on the larvae from Russia (western Caucasus) (Braasch 1978). The type series is currently deposited in the collection of Stuttgart State Museum of Natural History, Stuttgart, Germany (SMNS). Imagines (male and  female) and female subimago described by Braasch (1980) based on material from Russia, Armenia and Georgia. We assume the larva of E. (C.) magnus was erroneously described under the name znojkoi by Sinitshenkova (1976) (see remarks to E. (C.) znojkoi s. l. for details).
Habitat. Larvae inhabit small streams and rivers at low to high altitude. Altitudinal range of sampling sites 280-2100 m a.s.l. (Fig. 12). Most frequently found above 1000 m a.s.l.
Remarks. Taxonomy. This species was described based on larvae from Georgia (Kistinka River) (Sinitshenkova 1976). Type series is deposited in IZ (Kluge 1995). Male imago was described by Braasch (1979) based on the material from the western Caucasus (Teberda River) associated with larvae according to similar coloration of abdominal terga and sterna. Female imago not described. Male genitalia similar to E. (C.) caucasicus according to Braasch (1979).
Habitat. Larvae inhabit small streams and rivers at middle and high altitude in the western and central Greater Caucasus. Altitudinal range of sampling sites 570-2580 m a.s.l (Fig. 15). Most frequently found at altitudes above 1200 m a.s.l. Often syntopic with E. (C.) soldani and at higher altitude with E. (C.) sinitshenkovae.
Remarks. Taxonomy. This species was described based on the male imago and larva from western Greater Caucasus (Braasch 1979). The type series is currently deposited in SMNS. Imagines and larvae were associated based on the coloration of abdomen. Female imago not described.
Habitat. Larvae inhabit small streams and rivers at middle and high altitudes in the western and central Greater Caucasus. Frequently found above 1000 m a.s.l. Altitudinal range of sampling sites 426-1900 m a.s.l. (Fig. 18). Often syntopic with E. (C.) alpestris and E. (C.) sinitshenkovae.
Remarks. Taxonomy. This species was described based on male imago and larva from the western Greater Caucasus (Braasch 1979). The type series is currently deposited in SMNS. Larva associated with imago based on the coloration of abdomen.
Taxonomy. This species was described as a subspecies of E. (C.) caucasicus based on larvae collected in the Alborz Mts. (Braasch and Soldán 1979). Elevated to species level by Hrivniak et al. (2020b) based on a phylogenetic analysis of all Caucasian Epeorus (Caucasiron) species. The holotype probably lost. Paratypes are currently deposited in SMNS and Biology Centre of the Czech Academy of Sciences, Institute of Entomology, České Budějovice, Czech Republic (IECA). Imagines and subimagines not described.
Habitat. Larvae inhabit small streams and rivers at middle and high altitude in the western and central Greater Caucasus. Altitudinal range of sampling sites 760-2580 m a.s.l. (Fig. 24). Most frequently found above 1800 m a.s.l. Often syntopic with E. (C.) alpestris and at lower altitude with E. (C.) soldani.
Remarks. Taxonomy. Original description based on male imago and larva from the Greater Caucasus (Braasch and Zimmermann 1979). The type series is currently
Habitat. Larvae inhabit small streams and rivers at middle altitude in the central Greater Caucasus. Altitudinal range of sampling sites 903-1193 m a.s.l. (Fig. 27).
Remarks. Taxonomy. This species described based on male subimago and larva collected in central Greater Caucasus (Braasch 1980). The type series is currently deposited in SMNS. Larva associated with the subimago according to the coloration of abdomen. Male and female imagines not described.
Distribution. Known only from few sites in Samos Island (Fig. 30).
Habitat. Larvae inhabit small forested streams at 128-440 m a.s.l. (Fig. 30).  Taxonomy. This species was described by Braasch (1983) based on imagines as a subspecies of E. (C.) znojkoi. Elevated to species level in Hrivniak et al. (2020b) based on a phylogenetic analysis of all Caucasian Epeorus (Caucasiron) species. The type series is currently deposited in SMNS.
Distribution. Georgia, north-eastern Turkey, Armenia, south-western Russia (Fig. 33).    Habitat. Larvae inhabit streams and rivers of different sizes, from to middle-sized rivers at low altitude to small streams at high altitudes. Altitudinal range of sampling sites 40-1804 m a.s.l. (Fig. 33).
Remarks. Taxonomy. This species was described based on the larva, male subimago and imago (associated by rearing), female imago (associated by DNA analysis) and eggs. Material was collected from the western Lesser Caucasus (Hrivniak et al. 2017). The type series is currently deposited in IECA. Distribution. North-eastern Turkey, Georgia (Fig. 36). Known only from few sites in the Camili (Machakheli) District in Turkey and central Georgia.
Main morphological diagnostics of larvae.
Remarks. Taxonomy. This species described based on larvae collected from Pontic Mts. (Hrivniak et al. 2019). Imagines not described. The type series is currently deposited in IECA and collection of N. Kazancı and G. Türkmen (Hacettepe University, Department of Biology, Biomonitoring Laboratory, Turkey).  Distribution. Northern Iran. Species endemic to the Alborz Mountains (Fig. 39).
Remarks. Taxonomy. This species was described based on larvae collected from Alborz Mts. (Hrivniak et al. 2020a). Imagines not described.
The type series is currently deposited in SMNS, IECA, and Natural History Museum and Genetic Resources, Department of Environment, Tehran, Iran (MMTT_DOE).
Distribution. Northern Iran. Known only from three sites in the eastern Alborz (Fig. 42).
Distribution. South-western Iran. Known only from few sites in the central Zagros (Fig. 45).
Remarks. Taxonomy. This species was described based on larvae collected from Zagros Mts. (Hrivniak et al. 2020a). Imagines not described. The type series is currently deposited in SMNS, IECA, and MMTT_DOE. The lineage Caucasiron sp. 2 detected by Hrivniak et al. (2020b) is distributed in Turkey (Taurus Mts.) and morphologically corresponds to E. (C.) zagrosicus. Therefore, E. (C.) zagrosicus may represent a species complex.

Concluding remarks
This contribution represents the first complete source of information for the routine identification of the larvae of all fifteen Caucasiron species occurring in the Caucasus and adjacent areas. It is possible that additional new Caucasiron species will be de-   scribed from the region and some morphologically and genetically variable taxa, such as E. (C.) znojkoi, will be split into several species. This identification guide describes the state of the art at the time of publication.
All species of Caucasiron mayflies are charismatic animals, unique to the region. Some of them are endemic in a relatively limited area (especially for the Greater Caucasus and the Alborz Mts.) and may have considerable conservation value. We hope that this work will contribute to an increase in the knowledge of Caucasiron mayflies among hydrobiologists and ecologists. We would also like to encourage regional researchers to incorporate Caucasiron species as indicators in their biomonitoring surveys and water quality assessments.