Initial commented checklist of Iranian mayflies, with new area records and description of Procloeon caspicum sp. n. (Insecta, Ephemeroptera, Baetidae)

Abstract An initial checklist of mayflies (Ephemeroptera) of Iran is compiled based on critical review of available literature data, complemented with new data from 38 localities of Gilan and Ardabil provinces. At present, altogether only 46 species and 25 genera are known from Iran, 18 species are reported as new to Iran in this study. Some previously published data are critically evaluated and doubtful taxa are excluded from the list. Basic analysis of the distribution and biogeography of recorded species is given. Procloeon (Pseudocentroptilum) caspicum Sroka, sp. n. is described based on mature larva and egg. Critical differential diagnostic characters distinguishing the species from related taxa are discussed in detail.


Introduction
In comparison to Europe, the mayfly fauna of the Middle East is less known and data from some regions are still fragmentary. Extensive research on mayflies has been mainly focused on the Arabian Peninsula (Thomas and Sartori 1989, Sartori and Gillies 1990, Sartori 1991, Gattolliat and Sartori 2008 and neighbouring countries, namely Syria and Lebanon (Koch 1980, 1988, Thomas and Dia 1982, 1983, 1999, Thomas et al. 1988, Jordan (Gattolliat et al. 2012), and Israel (Demoulin 1973, Malzacher 1992, Sartori 1992, Yanai et al. 2017). Extensive literature is available from Turkey (for a review see Kazancı andTürkmen 2012 andSalur et al. 2016). In contrast, Iran, Iraq, Afghanistan, and Pakistan have been poorly investigated and only random findings of mayflies have been published to date (e.g., Kimmins 1950, Demoulin 1964, Allen 1973, Al-Zubaidi et al. 1987. Iran, the second largest (more than 1.6 million km²) country of the region after Saudi Arabia, has been studied only occasionally so far. Only 19 species of mayflies have been reported in 16 short taxonomic contributions published in international entomological journals. They include mostly simple faunistic records of species already known from neighbouring countries (Tshernova 1949, Soldán and Landa 1977, Braasch 1981, Kluge 1987, Soldán and Godunko 2013, Godunko et al. 2017). Descriptions of new species were often based on few specimens, often of a single developmental stage (Soldán 1978a, Braasch and Soldán 1979, Braasch 1981, 1983a,b, Sartori and Sowa 1992). The vast majority of records are limited to the northern part of Iran (mostly Alborz Mts. and its surroundings). The only comprehensive study of Iranian mayflies is a monography by Mohammadian (2005). It is written in Persian, thus inaccessible for a wider scientific audience. Moreover, it does not include new records, but is a mere compilation of literature without any own data contributed by the author. It enumerates 55 mayfly species presumably occurring in Iran. However, the list includes species reported from the Iranian Plateau, an area roughly extending from Tigris River to Indus River, which not only comprises Iran, but also some parts of neighbouring countries, Iraq, Azerbaijan, Turkmenistan, Afghanistan and Pakistan. Consequently, a significant part of the species listed should not be regarded as valid records actually documenting the occurrence of species in Iran unless being further corroborated.
Other sources of information on the mayfly diversity in Iran are some ecological studies on benthic macroinvertebrates over the last decades in order to assess water quality. Sharifinia (2015) reviewed 57 references (37 of them written in Persian) published after 2000 and compiled a list of 37 mayfly taxa (identified to species or genus level) known from Iranian rivers. However, this list is partially based on studies presenting species/genera which identity should be regarded as highly unlikely (Ahmadi et al. 2011, 2012, Mahboobi Soofiani et al. 2012, Amri et al. 2014, Farasat and Sharifi 2014, Golchin Manshadi et al. 2015. They list as many as 27 taxa (species or genera) known exclusively from the Nearctic and Neotropic Regions, the occurrence of which can be definitively excluded in the Middle East. Therefore, Sharifinia's as well as Mohammadian's lists of mayfly species should not be regarded as reliable, thus maintaining a significant gap in our knowledge. The area of Iran should be viewed a certain transitory zone hosting West Palaearctic (European) and Caucasian elements of fauna on one hand and Central Asian or even Oriental faunal elements on the other being certainly worth of the detailed and extensive study. Controversial or irrelevant distributional data should be deleted from faunistic lists, and existing data should be critically evaluated based on extensive, large-scale collecting of new material at localities covering the entire territory of Iran. The sine qua non condition is proper species identification even if requiring taxonomic revision of some taxa.
As a first step to achieve this ambitious goal, in May 2016 we collected mayflies at 38 localities in the Gilan and Ardabil Provinces in the north western Iran, the areas of presumably high Ephemeroptera diversity. This study represents the first part in a series of contributions aiming to provide a realistic and more complex picture of the Iranian mayfly fauna for future reference. Hence, the objective of the present study is to (i) critically review all mayfly records so far published from Iran with an emphasis on the validity of species occurrence in Iran and status of species from the taxonomic point of view, (ii) provide new data on the occurrence of species in the western part of the Caspian Sea region, and (iii) describe a new species of the genus Procloeon recently found in the studied area.

Study area
Mayflies were collected at 38 localities in the Gilan and Ardabil Provinces in 2016 ( Fig. 1). Studied localities included four types of landscape common at the region. (i) Five streams in the Caspian Sea coastal plains in the Gilan Province at the altitude from -6 to 40 m a.s.l. (localities No. 5,13,27,36,37 in Table 1). The Caspian Sea coastal plains are almost entirely covered by agricultural and urban land. Studied streams drained substantial area of rice fields and a mosaic of various croplands. Stream network of the Caspian Sea coastal plains was modified by numerous channels irrigating fields and interconnections of streams enabling needed distribution of water. Streams are often impacted by pollution from intensive agriculture and urban sewage. (ii) In total, 22 streams flow in the humid deciduous broadleaved forest at the northern slopes of the western part of the Alborz Mts. The altitude of the localities ranged from 80 to 820 m a. s. l. and they include relatively untouched, rapid, turbulent mountain streams (localities No. 6,11,15,17,32 in Table 1), shaded small, clear brooks (localities No. 2,7,8,10,16,28,30,31,33,34), and eutrophic streams influenced by agriculture and settlements in the river valleys (localities No. 1,3,4,9,18,35). (iii) Three streams (localities No. 12,14,29) were sampled above 1000 m a.s.l. in the Gilan Province and (iv) eight streams and one pond in the Ardabil Province (altitude 1430-2240 m a.s.l., localities [19][20][21][22][23][24][25][26]38). Localities in the Ardabil Province included only streams in the Sabalan Mt. (4811 m a.s.l.) environ. This region is prone to very extensive agricultural exploitation. Studied localities belong to the Euxino-Hyrcanian Province of the Euro-Siberian subregion of the Palaearctic Region (Sagheb Talebi et al. 2014). The climate is very humid, with cold winters, without dry period (annual precipitations 2000 mm, annual mean temperature 15 °C) in the western part of the Province and humid with mild winters and short dry period (annual precipitations 600 mm, annual mean temperature 18 °C) in its eastern part. The growing season lasts 7-9 months (Sagheb Talebi 2005, Sagheb Talebi et al. 2014. The Euxino-Hyrcanian Province is famous for its Hyrcanian and Arasbaran forest zones (Sagheb Talebi et al. 2014). The Hyrcanian Forest contains remnants of the broad leaf forests that covered most of the North Temperate Zone in the early Cenozoic (25-50 million years ago), as it was little impacted by Pleistocene climatic changes. Among 65 tree species known from the Hyrcanian Forest, there are several Tertiary relict species such as Caucasian zelkova Zelkova carpinifolia, Persian ironwood Parrotia persica, and Caucasian walnut Pterocarya fraxinifolia. Due to high humidity, the Hyrcanian Forest The Querco-Buxetum forests of the Caspian coastal plains have been almost completely converted to agricultural land. On the relatively less humid lower slopes of the mountains (below 700 m a.s.l.) in Gilan and Mazandaran provinces, chestnut-leaved oak (Quercus castaneifolia) and European hornbeam (Carpinus betulus) are mixed with Persian ironwood forming diverse Querco-Carpinetum and Parrotio-Carpinetum forests. These forests have been extensively exploited. Between 700-1500 m a.s.l., oriental beech (Fagus orientalis) is the dominant tree forming the Fagetum hyrcanum community, the most diverse and productive forest in the region, which is linked with European beech forests (Sagheb Talebi et al. 2014). Above the beech belt, Caucasian oak and Oriental hornbeam occur up to the timberline at approx. 2700 m a.s.l., forming the Querco macranthero-Carpinetum orientalis community (Sagheb Talebi 2005, Sagheb Talebi et al. 2014).

Materials and methods
Published records of mayfly species/genera in Iran were excerpted from available literature and summarised in Table 2. System and nomenclature of Palaearctic species included in Table 2 mostly follow Bauernfeind and Soldán (2012), with some exceptions (classification of Kluge and Novikova (2014) is used for the genus Nigrobaetis, Jacobus and Mc-Cafferty (2008) for the family Ephemerellidae). Generic and species names of Nearctic/ Neotropic species mentioned in ecological studies of Iranian freshwaters were presented in the original form, later taxonomic or nomenclatoric changes were not taken into account. Table 2. Commented list of Ephemeroptera of Iran with notes to their distribution. Species representing new area records to Iranian mayfly fauna are in bold, data on taxa with unlikely occurrence are marked with an asterisk (*). See Table 1 for numbers and for precise location of localities in the Gilan and Ardabil Provinces studied recently. Basic information on the area of species is based on Bauernfeind and Soldán (2012), detailed information concerning the Middle East and Central Asia is provided by references. Data on the occurrence of solely Nearctic/Neotropic species and genera are mentioned below the Unidentified species reported from unclear locality 117 km S of Rasht by Braasch (1981). Family Ametropodidae reported from the unnamed stream NW of Shiraz by Bashti and Ostovan (2014). The nearest record of the genus (Ametropus fragilis) was published from the Caucasus (Eaton 1883-1888, Sadovsky 1940 Mousavi and Hakobyan (2017; Haraz riv., Dalir riv., Chatan riv., Firuz Abad riv.), Seyyedsharifi et al. (2014;Gharasou riv.), Farasat and Sharifi (2014;Kavat riv.), Mahboobi Soofiani et al. (2012;Zayanderud) and Braasch (1981, 50 km SE of Khorramabad).
A species close European representatives to the B. alpinus species-group. Reported by Amri et al. (2014). The occurrence in Iran is rather unlikely as its westernmost records were published from Mongolia.  1987) and Turkey (Kazancı andTürkmen 2012, Salur et al. 2016).

Baetis
Iran falls within its known distributional range.
B. buceratus species-group. Iran represents the easternmost limit of its area.
Iran represents easternmost limit of its area. Material shows some morphological differences from European material and requires more detailed examination.  Eaton, 1870 in the larval stage.

B. fuscatus mentioned by Eaton (1885) as "… eastwards to Southern
Persia (Hagen Mus)". Iran falls within known distributional range of both species.
Iran represents the easternmost limit of its area. Larvae of B. lutheri species-group from N Iran can be confused with poorly known species Baetis petrovi Tshernova, 1938 (see Soldán and Godunko 2008).
Iran represents the easternmost limit of its area.
Iran represents the easternmost limit of its area.  Novikova and Kluge 1994). Known also from Korean peninsula and Japan.
Iran falls within its known distributional range.

Species/genus Records from Iran Notes to the global area and distribution Remarks to records in Iran
Baetis ( Poorly known species, so far considered endemic to the Caucasus (Jacob and Zimmermann 1978).
Only 20 larvae known from the Caucasus to date (Jacob and Zimmermann 1978). Findings from Iran represent the second published records on its so far insufficiently known area.  Müller, 1776 andC. pirinense Ikonomov, 1962.
Our records represent undescribed species related to C. luteolum. The species will be described by Martynov (pers. comm.) based on the material from Caucasus (AR Adjara). Unidentified species of the genus Centroptilum was also reported by Mahboobi Soofiani et al. (2012) from Zayanderud in Central Iran.

Species/genus Records from Iran Notes to the global area and distribution Remarks to records in Iran
Procloeon (Pseudocentroptilum) caspicum sp. n.
Gilan Prov.: 7, 27 (type locality), 36 So far known from the type locality in Iran only.
Single record from the type locality (Braasch 1983a), no record since then.
Common and often abundant species in streams studied in the Gilan Prov., preferring forest streams and rivers at lower altitudes.
Common and often abundant species in streams studied in Gilan Prov., preferring forest streams and rivers with no apparent altitude preference. At lower stream sections syntopic with E. pseudaffinis.
Single record from the type locality, no record since then.
The most common Epeorus (Caucasiron) species recorded at the streams studied in Gilan Prov. Iran represents the easternmost limit of its known distribution.
Common species in the Gilan Prov. Braasch, 1983 Shesavar (type locality), likely referring to Shahsavar Known only as the holotype (male imago) and paratypes (two female subimagines) described by Braasch (1983b) from a single locality.

Rhithrogena paulinae
Only holotype (imago male) and paratypes (four female imagos and two larvae) from a single locality known (Sartori and Sowa 1992).
Known only from the Alborz Mts.
Holarctic genus, six species known from the West Palaearctic Region.

Species/genus Records from Iran Notes to the global area and distribution Remarks to records in Iran
Paraleptophlebia submarginata (Stephens, 1935) "50 km SE of Khorramabad, 1500 m a.s.l." Widely distributed in Europe (from Fennoscandia to Mediterranean), in northeast reaching to Ural and W Siberia (e.g., Novikova 1984, Beketov andKluge 2003), and southeast to Israel (Sartori 1992) and Iran (Braasch 1981).
The only record from Iran with insufficient localisation (Braasch 1981).
The record from Iran is based on the type series only (Chopra 1927) which is, however, insufficiently localised ("Seistan, Persia"). The author described the species based on imagines and mentioned that "the nymphs have been described by Graverly in detail". Graverly (1920) described the nymphs as "Palingenia (s. str.) ? longicauda, Olivier" and the material is localised as "Randa stream 4 miles NW of Jellalabad, Seistan".

Caenidae
Caenis sp. Mayfly larvae were collected by T. Soldán, J. Bojková and J. Imanpour Namin from 12 to 22 May 2016, using metal strainers after kick-sampling. Sampling of larvae for about 30-60 minutes was supplemented by sweeping of imagines and subimagines from riparian vegetation by a standard entomological net. The material studied in the present contribution sums up to 9213 larval specimens and 245 subimagines and imagines. Most material is deposited in the collection of the Biology Centre, Czech Academy of Sciences, Institute of Entomology, České Budějovice, Czech Republic. Reference specimens for the species recorded are deposited in the collection of J. Imanpour Namin (Department of Fishery, University of Gilan). All specimens were preserved in 96% ethanol. Some specimens were mounted on slides with HydroMatrix (MicroTech Lab, Graz, Austria). Drawings for the descriptions of the new species were made using a stereomicroscope Olympus SZX7 and a microscope Olympus BX41, both equipped with a drawing tube. Photographs were made using a Canon EOS 1200D camera mounted on a Leica M205 C stereomicroscope. All photographs were subsequently enhanced with Adobe Photoshop CS5. For scanning electron microscopy, samples were gradually transferred to acetone, critical point dried and coated with gold by sputtering using a Baltec SCD050 Sputter Coater. Observations were taken on the scanning microscope Jeol JSM 7401F at 4 kV (BC CAS, České Budějovice). Eggs were dissected from a pharate female subimago.
Head. Labrum (Fig. 4) approximately 1.3 × broader than long, anterior margin with pronounced medial notch. Anterior margin laterally from medial notch strongly asymmetrically rounded. Along anterior margin, row of bifurcated setae situated anterolaterally and shorter, stout setae anteromedially. Dorsal surface with scattered hairlike setae, not arranged in rows; ventral surface with group of hair-like setae medially. Mandible incisors (Figs 5, 6) divided into two groups, separated at distal third of their length. Each group with 3-4 rounded denticles. Left prostheca broadened apically, with approximately three blunt teeth and four longer sharp teeth (Fig. 5); right prostheca not broadened apically, with approximately three blunt teeth and one longer sharp tooth (Fig. 6). Group of long setae present between incisors and molar area. Maxillary palps (Fig. 7) 3-segmented, second slightly shorter than first segment. Third segment approximately half as long as second segment, apically tapering, bluntly pointed, without scales. Maxillary palps sparsely covered with tiny hair-like setae. Labial palps 3-segmented (Figs 8, 10), third segment with rounded angles and straight margin apically. Ventral side of first and second segment with scattered hair-like setae, third segment with several longer and thicker setae (particularly along apical margin) and numerous hair-like setae (Fig. 8). Dorsal side of second segment with group of 4-7 long setae, otherwise dorsal side of all segments without setae (Fig. 10). Glossae as broad as paraglossae, paraglossae slightly longer. Paraglossae ventrally with single irregular submarginal row of setae along inner margin, basal parts of glossae and paraglossae with sparse groups of long hair-like setae (Fig. 9). Glossae and paraglossae dorsally with rows of setae along margins (longer setae on paraglossae, shorter on glossae), denser setation apically, one additional irregular row of long setae in median portion of paraglossae (Fig. 11).
Abdomen. Terga whitish, with dark spots forming clear pattern (Figs 2, 3). Terga I-VIII with dark spot posterolaterally (on segments I-VII near respective gill insertion). Tergum I with dark stripe on posterior margin. Tergum II with distinct dark patch medially, wide band (sometimes interrupted in middle) along anterior margin and thinner stripe on posterior margin, fused with enlarged smudges situated posterolaterally. Tergum III similar to tergum II, band along anterior margin more distinct, sometimes fused with posterolateral smudges. Tergum IV pale, with thin stripe on posterior margin and indistinct smudges medially and laterally. Terga V-VI with dark patch medially and dark stripe on posterior margin, fused with enlarged smudges situated posterolaterally. Tergum V also bears distinct dark band along anterior margin, connected to posterolateral smudges. Tergum VII with thin dark stripe on posterior margin and slightly wider stripe along anterior margin, interrupted in middle. Tergum VIII with wide dark band along posterior margin. Tergum IX with thin dark stripe on posterior margin and wide dark band anteriorly (most dark areas on anterior margin and laterally). Tergum X with dark stripe on posterior margin. Sterna pale whitish with dark patches sublaterally and dark stripe on posterior margin. Distinctiveness of this pattern increasing in more posterior segments. Sterna VIII-IX all dark smudged. Surface of abdomen covered with numerous scales and scale bases (Fig. 30); similar scales also on legs and other body parts. Posterior margin of abdominal terga I-IX with large teeth accompanied by smaller ones (Figs 25,30). Teeth on tergum X smallest medially, lateral teeth slightly longer (Fig. 26). Segments II-VII with 1-2 prominent posterolateral spines near gill bases, sometimes accompanied by few smaller ones. Lateral spines present on segments VIII-IX (Fig. 17). Gills  whitish, with distinct tracheization. All gills simple, vestigial dorsal lamella present. Gills asymmetric and apically rounded. Paraproct (Fig. 27) with approximately 8-11 large teeth accompanied with scarce smaller ones on inner margin. Ventral surface of paraproct plate covered with scales, scale bases, and tiny hair-like setae. Caudal filaments reaching approximately 1/3 of body length, yellowish, with dark brownish stripe in middle. Paracercus slightly shorter than cerci. Ring of small triangular spines at each articulation of caudal filaments, alternated with larger spines every fourth segment (Fig. 31, these larger spines accompanied by dark brown stripe and distinction more pronounced in basal part of filament). Articulations further equipped with flattened scales and scale bases. Long swimming setae along inner margin of cerci and on both margins of paracercus. In basal third of filaments swimming setae only scarce, apically only last one or two segments without setae. Outer margin of cerci with enlarged, long, and thick spines on distal segments, longer than corresponding segment (Fig. 28).
All types deposited in the collection of the Biology Centre, Czech Academy of Sciences, Institute of Entomology, České Budějovice, Czech Republic.
Etymology. The species name refers to the proximity of the type locality to the Caspian Sea.
Habitat. Larvae were found in three different stream habitats, two eutrophic streams of different size (Chelvand and Karganrud rivers) in the Caspian Sea coastal plain relatively close to their inflow to the sea and one small, clear and cold brook in the forest. Chelvand at the type locality is a small river with coarse stony substratum rapidly flowing from the hills to the plain so it partially keeps its mountainous charac-ter also in low altitude (-6 m a.s.l.). Procloeon caspicum sp. n. larvae co-occurred with numerous larvae of Serratella elissa, Baetis vardarensis and Caenis macrura, and less numerous Epeorus (Caucasiron) spp., Rhithrogena cf. decolorata. Karganrud in Talesh is a warm river flowing in the urban and agricultural area with wide flat alluvium and stony-gravel substratum. Bottom substrate had rich cover of green filamentous algae. Procloeon caspicum sp. n. co-occurred with numerous larvae of Rhithrogena cf. decolorata, Oligoneuriella tskhomelidzei, Baetis vardarensis, Baetis rhodani, and less numerous Baetis fuscatus and Serratella elissa. Sefidab, the third and completely different stream, is a small cold brook entirely shaded by forest with coarse stony bottom and alternating pools and riffles. Procloeon caspicum co-occurred with numerous larvae of Epeorus (Caucasiron) cf. znojkoi, Electrogena pseudaffinis, Baetis baroukianus and less numerous Serratella elissa and Habroleptoides confusa.

Affinities of Procloeon (Pseudocentroptilum) caspicum sp. n.
Within the subfamily Cloeoninae, several views on the (sub)generic classification have been published, most recently by Jacob (1991), Kluge and Novikova (1992), Bauernfeind and Soldán (2012), and Kluge (2016). All these authors recognize basically the same higher taxa, the difference is mostly in the hierarchical structuring and grouping of individual (sub)genera. All concepts use some characters of unclear polarity and/or derived characters prone to convergence to define individual taxa, thus all represent more or less "working versions" until a large-scale phylogenetic analysis of Baetidae is accomplished.
In this study, we follow Bauernfeind and Soldán (2012), where the new species is attributable to the genus Procloeon Bengtsson 1915. Procloeon caspicum sp. n. corresponds with all diagnostic characters given for Procloeon by Bauernfeind and Soldán (2012), most importantly the presence of long, blade-shaped, apicolateral spines in distal part of cerci. This character is suggested as synapomorphy of the clade Procloeon + Pseudocentroptiloides by Kluge and Novikova (1992), who treated both taxa as subgenera of Cloeon. Within Procloeon sensu Bauernfeind and Soldán (2012), the new species is attributable to the subgenus Pseudocentroptilum Bogoescu, 1947, based on the presence of hind wings and mandibular incisor groups separated in apical part only. This subgenus contains 18 species distributed in the Holarctic and Oriental regions (Bauernfeind and Soldán 2012).
The new species is characterized by a relatively uncommon (within Procloeon) combination of two characters, i.e., the presence of fully developed hind wing pads and single gill plates. Such a combination is present in three Procloeon species only, namely Procloeon (Pseudocentroptilum) albisternum (Novikova, 1986), Procloeon (Pseudocentroptilum) maritimum (Kluge, 1983) and Procloeon (Pseudocentroptilum) calabrum (Belfiore & D'Antonio, 1990). Occurrence of these species in Iran is extremely unlikely, since the former two species are distributed in the Far East -Russia (Novikova 1987, Kluge 1983, Tiunova 2009) and South Korea (Bae and Park 1997), and the latter species is endemic to a very small area of southern Apennine (Belfiore pers. comm.). Furthermore, these species can be differentiated from P. caspicum sp. n. using several morphological characters: Both P. albisternum and P. maritimum differ from P. caspicum sp. n. in the absence of rudimental dorsal lamella of gill plates (figs 105-109 in Kluge 1983, fig. 2 in Novikova 1987. The extent of the dorsal lamella reduction may exhibit intraspecific variability within Cloeoninae (e.g., in related Procloeon (Pseudocentroptilum) heterophyllum Kluge & Novikova, 1992, the minute dorsal lamella may be present or absent, see figs 1-14 in Kluge and Novikova, 1992).
However, in contrast to P. caspicum sp. n., P. albisternum possesses a different shape of labrum (almost rectangular with a very shallow notch in the middle of anterior margin), more deeply divided mandibular incisors, and a two-segmented maxillary palp ( fig. 1 in Novikova 1987). P. albisternum is equipped with lateral spines on abdominal segments II-IX (only on segments VIII-IX in P. caspicum sp. n.) and has a different shape of gill plates, in particular gills II-IV being more asymmetric with the inner margin extended anteriorly ( fig. 2 in Novikova 1987).
Procloeon maritimum differs in the shape of maxillary palp, which is apically rounded and distinctly thicker in P. maritimum compared to P. caspicum sp. n. (figs 5, 20 in Bae and Park 1997). Moreover, length of the apical segment of maxillary palp reaches less than 1/3 the length of segment II (Bae and Park 1997), compared to approximately 1/2 in P. caspicum sp. n. Tarsal claws are slightly shorter in P. maritimum, reaching 0.38 × foretarsus length compared to 0.44 × in P. caspicum sp. n. and 0.45 × middle and hind tarsus length compared to 0.55 × in P. caspicum sp. n. (see Kluge 1983). The arrangement of the inner margin of paraproct also slightly differs, with a higher number of teeth of more irregular size occurring in P. maritimum ( fig. 110 in Kluge 1983).
Procloeon calabrum can be reliably distinguished from P. caspicum sp. n. based on several characters. It differs in the shape of labrum, with medial notch on anterior margin much more pronounced in P. caspicum sp. n. compared to P. calabrum. Anterior margin laterally from the medial notch is symmetrically rounded in P. calabrum (fig. 9 in Belfiore and D'Antonio 1990), whereas it is strongly asymmetric in P. caspicum sp. n. (Fig. 4). Maxillary palps are only two-segmented in P. calabrum, contrary to a distinguishable third segment in P. caspicum sp. n. Another diagnostic character is represented by the length of tarsal claws (see . In P. calabrum, tarsal claws in forelegs are equal to 3/4 of tarsi, in middle and hind legs hardly reaching 3/4 of tarsi (Belfiore and D'Antonio 1990). In P. caspicum sp. n., tarsal claws in all legs are distinctly shorter (see . The egg chorion of P. caspicum sp. n. also lacks the equatorial band of large papillae, present in P. calabrum. List of species known from Iran. A detailed review of literature revealed 42 references published in international journals accessible to the scientific public. Publications written in Persian (Farsi) were previously reviewed by Sharifinia (2015) and they did not include any species not reported in international sources reviewed (cf. Table 2 summarizing macroinvertebrate diversity in Sharifinia 2015). Despite relatively high number of recent (after 2000) publications on macroinvertebrates based on routine sampling of benthic communities, the knowledge on aquatic diversity seems to be very limited. Most studies include data on macroinvertebrates determined to family level (e.g., Nemati Varnosfaderany et al. 2010, Montajami et al. 2012, Abbaspour et al. 2013, Bashti and Ostovan 2014, Eyidozehi et al. 2014, Nasirian 2014, Aazami et al. 2015, Shayeghi et al. 2016 or generic level only (e.g., Egglishaw 1980, Mousavi Nadushan and Ramezani 2011, Mahboobi Soofiani et al. 2012, Imanpour Namin 2013, Ghasemi and Kamali 2014, Seyyedsharifi et al. 2014, Shokri et al. 2014, Shayeghi et al. 2015, Sharifinia et al. 2016a, reporting predominantly common Palaearctic families and genera. Unfortunately, determination to species level (if present) is erroneous in most cases in question. Altogether 27 records of species or genera (Table 2, comments below) with restricted distribution to the Nearctic and Neotropic Region are listed, suggesting that the authors used inappropriate determination keys. For example, the listed Nearctic/Neotropic genus Lachlania in fact most likely represents Oligoneuriella that is widely distributed in north Iran (cf. Table 2); the same concerns the Nearctic/ Neotropic genus Campsurus which in fact most probably represents Ephoron. Likewise, the Nearctic/Neotropic genus Callibaetis could refer to cosmopolitan Cloeon, and the Nearctic/Neotropic genus Tricorythodes seems to refer to cosmopolitan Caenis, etc. A review of macroinvertebrates of Iranian running waters by Sharifinia (2015), despite promising "critical re-identification of the reported species", includes such confusing data not only in mayflies, but also in Plecoptera. Therefore, we do not recommend using this list as reliable and valid source of information on the diversity of Iranian benthic insects. Relevant information on mayfly diversity was only found mainly in 20 th century publications in international entomological journals. However, these are highly fragmented and refer to material often limited to occasional collections with only several specimens examined. Moreover, these records are almost completely confined to the northern part of Iran, mostly Alborz Mts.
Broadening literature data with new material sampled in 2016, we conclude altogether 48 species records and 22 records at generic/subgeneric level of determination ( Table 2). Records of Nearctic/Neotropic species and genera were excluded. We included all records of species and genera distributed in the Palaearctic Region, although we regard the occurrence of seven of them as doubtful. This concerns species/genera which have never been recorded at such low latitude (Ameletus, Arthroplea, and Leptophlebia) and so easternmost (Siphlonurus, Ephemerella maculocaudata) or westernmost (Cinygmula, Baetis bicaudatus) in the West Palaearctic Region. The genus Arthroplea, although exhibiting some southern area disjunctions in Europe, is predominantly boreal (Bauernfeind and Soldán 2012) and thus, its occurrence in the Middle East could be excluded. The genus Leptophlebia shows similar distribution as Arthroplea (although not so strictly boreal) in the West Palalearctic Region and is missing even in eastern Mediterranean and Caucasus. The occurrence of Ephemerella maculocaudata in Iran is very unlikely as its easternmost records are from the Balkans (Bulgaria and Macedonia). This record most probably refers to the recently described Serratella elissa, as its larvae similar to E. maculocaudata exhibit few basal dark brown segments of cerci (cf. Soldán 1982). Moreover, S. elissa is very common and abundant in the coastal area of the Caspian Sea and the type locality of S. elissa is about 150 km far from the locality of E. maculocaudata. The remaining four doubtful records are not fully improbable and need to be confirmed. The genus Siphlonurus, common in Europe, Far East and Japan, is very sparsely distributed in eastern Turkey and western Caucasus, but missing in the Middle East countries and Central Asia (Bauernfeind and Soldán 2012). The genus Ameletus is widely distributed in Europe, Siberia, Central Asia and Far East, however, its southern area border is insufficiently known (Bauernfeind and Soldán 2012). It occurs in Turkey but is missing in the Caucasus. The western limit of the areas of the genus Cinygmula and Baetis bicaudatus is in Central Asia and Mongolia, respectively (Bauernfeind and Soldán 2012). Moreover, the genus Cinygmula can be easily confused with the genus Rhithrogena.
Excluding B. bicaudatus and E. maculocaudata as discussed above, 46 reliable species were recorded, 18 species of them were recorded to Iran for the first time (in bold in Table 2). These species can be classified into the following groups from the biogeographical point of view.
(i) Holarctic and Transpalaearctic species form the minority of the mayfly fauna of Iran, encompassing six eurytopic species: Baetis fuscatus, Baetis rhodani, Cloeon simile, C. cognatum, C. dipterum, and Serratella ignita. Concerning the genus Cloeon, there are persisting taxonomic and determination problems, especially in the subgenus Cloeon s. str. and actual findings in Iran, thus, should be considered with caution. Likewise, B. rhodani is currently considered a polytypic species with the cryptic species throughout the geographical range (Williams et al. 2006).
(ii) West Palaearctic species with southern area limit in the Middle East included 13 species. Most of them are widely distributed throughout the whole area: Baetis buceratus, B. lutheri, B. nexus, B. vardarensis, Paraleptophlebia submarginata, Habroleptoides confusa, Habrophlebia lauta, Ephemera danica, Palingenia longicauda, and Caenis macrura (Bauernfeind and Soldán 2012). Iran is the natural south eastern area limit for many West Palaearctic species since the Caspian Sea, arid areas in central Iran, and large deserts in east Iran are the barriers separating Central Asia and the Indian subcontinent. Three species, Palingenia fuliginosa, Heptagenia samochai and Epeorus zaitzevi, show a peculiar central Palaearctic distribution, missing in central, northern and western Europe. P. fuliginosa shows an arc-like area spreading from eastern Slovakia and Ukraine to Caucasus and Caucasian part of north Iran (Soldán 1978b, Bauernfeind andSoldán 2012). Heptagenia samochai is distributed in Israel and from the Crimean Peninsula and Transcaucasia to Iran (Bauernfeind and Soldán 2012). E. zaitzevi is known from several Middle Eastern countries (Israel, Iraq, Syria, and Turkey) and from the Caucasus (Azerbaijan and Armenia) (Kluge 1997b, Bauernfeind andSoldán 2012).
(iii) West Palaearctic species with area disjunction to Central Asia, Baetis gracilis to Tajikistan, B. muticus to Kazakhstan (Bauernfeind and Soldán 2012), and Baetis braaschi distributed continuously from the Eastern Ukraine, Crimea and Caucasus Mts. through Iran and Turkmenistan to Central Asia .
(v) Near and Middle East species include those described and known from Iran only: Procloeon caspicum sp. n., Electrogena bothmeri, Rhithrogena iranica, R. paulinae, Epeorus caucasicus iranicus, and Serratella elissa. Most of them are insufficiently known; E. bothmeri and R. iranica were described based on imagines (subimagines) only, the status of the latter species should be revised. The same concerns Electrogena ressli described from Turkey with paratypes from Gilan Province in Iran. On the contrary, only larvae were described in E. caucasicus iranicus, S. elissa and P. caspicum sp. n. Real distribution of all these species is unknown. Other species are, beside Iran, known from a single neighbouring country: Baetis baroukianus (Lebanon), Baetis monnerati (Jordan), Choroterpes sumbarensis and Caenis kopetdagi (Turkmenistan), Teloganopsis subsolana (Afghanistan), Mortogenesia mesopotamica (Iraq), Palingenia orientalis (Israel), and Clypeocaenis bisetosa (India). The only exception is B. samochai which inhabits the whole Near East (Turkey, Israel, Lebanon, Syria, and Iran).
Most studies and records on mayflies are available from northern Iran which belongs to Euxino-Hyrcanian Province of the Euro-Siberian subregion of the Palaearctic Region (Sagheb Talebi et al. 2014). They provide a good example of species of West Palaearctic (or European) origin with eastern area limits in Iran. Additionally, the Caucasian faunistic elements are reaching eastwards the northern mountains (Alborz Mts., Talysh Mts., Arasbaran Mts. and their foothills). Future detailed research will probably reveal a closer relation to the Caucasus bioregion and simultaneously, some endemic species could be expected there. This region is exceptional and attractive for scientists due to the Hyrcanian Forest, which is the hot spot of biodiversity of flora and fauna (Tohidifar et al. 2016). The Caspian Hyrcanian Forest in Iran and Azerbaijan is among the last extensive relicts of temperate primeval forests in the world hosting diverse insect specialists that are extinct in Europe and other parts of the world (see Müller et al. 2015Müller et al. , 2017. In contrast, knowledge on mayflies of the large area of central Iran, biogeographically belonging to the Irano-Turanian Province of the Central Asian subregion, is insufficient. This area includes arid and desert Central Plateau and large mountain range of Zagros Mts., which hardly ever were investigated. Local endemic species restricted to isolated or relict aquatic biotopes can hypothetically be discovered in this region. The southernmost part of Iran belongs to the Saharo-Sindian Province of the Euro-Siberian subregion, which covers also several other Middle East countries, such as neighbouring Iraq, part of Saudi Arabia and Syria. The occurrence of faunistic elements from the western part of this Province (Arabian Peninsula and North Africa) in the southern Iran can be hypothesized. Unfortunately, there are no data on mayflies from southern Iran to date.
This list of Ephemeroptera of Iran is undoubtedly preliminary and incomplete due to limited literature sources and lack of correct determination of material collected for water quality assessment. Thus, the total number of 46 species recorded is very low and does not represent the real diversity of mayflies in Iran. In comparison, Odonata, a very attractive and popular group of aquatic insects, have been better investigated at least from the faunistic point of view, with records of 100 species and subspecies throughout Iran (see current check list by Heidari and Dumont 2002 and many recent studies: Ebrahimi et al. 2009, Sadeghi and Mohammadalizadeh 2009, Ghahari et al. 2009, 2012, Eslami et al. 2014, 2015, Kiany and Sadeghi 2016. Likewise, faunistic records of Trichoptera include 130 species (see current check list by Mirmoayedi and Malicky 2002 and some important recent studies: Malicky 2004, Mey 2004, Chvojka 2006, pointing at the real diversity of the area. Comparatively less is known about Iranian stoneflies, which were studied in detail only in the northern part of the country (Aubert 1964, Murányi 2005, or aquatic beetles (e.g., Olmi 1981, Vafaei et al. 2007, 2009, Ghahari and Jedryczkowski 2011, Ghahari et al. 2015, Jäch et al. 2016). However, the distribution and diversity of all these aquatic groups were investigated predominantly based on their adults and/or terrestrial stages. Larvae of many species have not been described yet and, consequently, virtually nothing is known on their biology and ecological requirements.
To fill evident gaps in our knowledge resulting from this review, we aim to work on a more extensive study of Iranian Ephemeroptera covering the geographical gradients within Iran. This may unravel unknown species and diversity in different biogeographical provinces of Iran. This however would require to set up a network of localities and to study at least some of them in different seasonal aspects. Our first field trips to Iran in 2016 and 2017, however, showed us that aquatic ecosystems have been under strong, long-term anthropogenic pressure and some areas unfortunately presumably no longer maintain their original aquatic biodiversity. We observed many rivers with severe pollution that most probably wiped out local populations of the aquatic fauna. Overexploitation of water sources and growing pollution from fertilisers, pesticides and municipal and industrial wastewaters are serious threats to aquatic biodiversity. Iran has 7.2 million ha of agriculture land dependent on irrigation, the largest area in the Middle East, thus, agricultural use accounts for more than 90% of total water withdrawal. About 1.7 million ha of irrigated land is affected by salinization (World Commission on Dams 2000, Afkhami 2003). About 96 % of the urban population of Iran is connected to public water supplies; however, only 16 % are connected to adequate sewage treatment facilities (see Charkhabi et al. 2005, Afkhami et al. 2007). There are also significant problems caused by insufficient treatment of industrial wastewaters leading to serious impacts of heavy metals and other toxic compounds (e.g., Gheshlagh et al. 2013, Khodadadi et al. 2013, Mollazadeh et al. 2013, Majnoni et al. 2015 which affect, beside aquatic ecosystems, also human health (e.g., Karrari et al. 2012). Moreover, the absence of real regulations of water abstraction from rivers and lakes and obligatory minimal flows from impoundments seriously impacts hydrology of streams and their ecosystem functioning. It underlines the importance to study both regional and local aquatic diversity until it totally disappears. The discovery of possible refugia for aquatic biota, which should be proposed as priority for immediate conservation, is an urgent goal to preserve the aquatic biodiversity of Iran. However, only thorough basic taxonomic and faunistic research can contribute to water and conservation management set by the local authorities.