Epeorus (Caucasiron) himalayensis Hrivniak & Sroka 2025, sp. nov.
Creators: name: Hrivniak, Ľuboš
name: Sroka, Pavel
name: Godunko, Roman J.
name: Martynov, Alexander V.
name: Palatov, Dmitry M.
name: Bojková, Jindřiška
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Ephemeroptera
Heptageniidae
Epeorus
Epeorus himalayensis

description: Epeorus (Caucasiron) himalayensis Hrivniak & Sroka sp. nov.
Figs 3, 4, 5, 6
Type material.
Holotype: • male larva: India: Uttarakhand Pradesh, vicinity of Pandukeshwar village, left tributary of Alakananda River, 2099 m a. s. l., 30°38.901'N, 79°32.108'E (codes: IND 2018 / 7; 39 Gang); 9–11.05. 2018, Martynov A. V., Palatov D. M. leg. Paratypes: • 12 larvae (barcoded specimens: IN 1, SP 11 - labrum and mandibular incisors mounted on slide, SP 12), 4 male imagoes (reared from larvae; barcoded specimens: IN 7 - genitalia and larval exuvia mounted on slide, IN 8, IN 9), 3 female imagoes (reared from larva; two larval exuviae mounted on slide), 1 male subimago (reared from larva): same data as holotype. • 2 larvae (barcoded specimens: SP 13, SP 22): India: Uttarakhand Pradesh, vicinity of Lambagad village, Alaknanda River, 1998 m a. s. l.; 30°38.64198'N, 79°32.02500'E (codes: IND 2018 / 8; 40 Gang); 9–11.05. 2018, Martynov A. V., Palatov D. M. leg.
Etymology.
The species name himalayensis (Latin) refers to the distribution in the Himalayas.
Description of larva.
General coloration yellowish brown with dark brown maculation (Fig. 3). Body length (BL) of late-instar larvae: 15.0 mm (female; n = 1), 11.8–13.1 mm (male; n = 3). Length of cerci approximately 1.2 × body length.
Head. Shape trapezoidal, slightly rounded (Fig. 3 D, E). Head dimensions of late-instar larvae: length 3.3 mm, width 5.0 mm in female; length 2.5–2.6 mm, width 4.0– 4.1 mm in male. Width / length ratio: 1.48–1.57 (female; n = 8), 1.48–1.64 (male; n = 8). Coloration pattern of dorsal surface consists of: i) paired stripe-like and rounded maculae along epicranial suture, ii) pair of triangular (or blurred) macula near inner edges of eyes, iii) pair of rounded maculae ventrally to lateral ocelli, iv) pale stripes extending from lateral ocelli to lateral edges of head, v) rectangular macula between ocelli, vi) stripe-like and rounded maculae ventrally to median ocellus. Antennae yellowish brown, scapus and pedicellus darkened (Fig. 3 D, E). Dorsal surface covered with short rounded spatulate setae (as on abdominal terga; Fig. 4 E), fine hair-like setae and stick-like setae. Sparse longer and fine hair-like setae located posteriorly to eyes.
Mouthparts. Labrum (Fig. 4 A) widened anteriorly; anterior margin slightly rounded or nearly straight. Lateral angles rounded. Dorsal surface covered with setae of different size, 4–6 longer bristle-like setae located antero-medially and two bristles antero-laterally (Fig. 4 A, left half). Epipharynx with longer, slightly plumose bristles situated along lateral to anterior margin, cluster of fine, hair-like setae medially (not figured), and group of 6–12 setae of various size (Fig. 4 A, right half). Outer incisors of both mandibles with three apical teeth; outer tooth blunt in both mandibles. Inner incisor of left mandible with three apical teeth (Fig. 4 B), right inner incisor bifurcated (Fig. 4 C).
Thorax. Prothorax anteriorly narrowed, lateral edges slightly rounded. Metanotum with small blunt posterior-median projection. Dorsal surface covered with hair-like setae, stick-like setae and short rounded spatulate setae (as on abdominal terga and head). Sparse longer, hair-like setae along pro-, meso- and metanotal suture.
Legs. Coloration on Fig. 3 H, I. Femora with median hypodermal spot, often transversely extended. Base and apex of femora darkened; patella-tibial suture darkened; tarsi proximally and distally darkened. Dorsal surface of femora covered by short rounded spatulate setae (Fig. 4 D), hair-like setae and sparsely distributed stick-like setae. Dorsal edge of femora with blade-like setae. Dorsal margin of tibiae and tarsi with row of dense hair-like setae; ventral margin with irregular row of distally accumulated spines. Tarsal claws with two or three denticles.
Abdominal terga. Color pattern of abdominal terga consists of transversal stripe along anterior margin of terga I – IX (X), medially extending to: i) triangular or blurred macula on terga II – IV and ii) triangular or T-shaped macula on terga V – IX (median macula on terga VIII and IX widened) (Fig. 3 F, G). Pair of short stripes or spots present antero-laterally to median maculae. Lateral margins with oblique stripe-like maculae on terga I – IX (often dorso-posteriorly extended). Denticles along posterior margin of terga dense, irregular, and pointed (Fig. 4 F). Surface of terga covered with hair-like setae, stick-like setae and rounded spatulate setae (Fig. 4 E, F). Tergum X with short posterolateral projections (Fig. 4 L, arrow). Terga with longitudinal median row of hair-like setae.
More or less developed posteromedian spine (best expressed on terga VII – IX as on Fig. 11 M, N) were observed in larvae of BL 6.0– 8.2 mm (barcoded specimens SP 12, SP 13, SP 22). Tergal spines were not observed in late instar larvae and last instar larval exuvia from reared adults (barcoded specimens: IN 1, IN 7, IN 8, IN 9).
Abdominal sterna. Yellowish, with a pattern consisting of more or less defined triangular maculae (Fig. 3 K – N). Nerve ganglia darkened. Sternum IX of female with V-shaped median emargination and numerous hair-like setae (Fig. 4 M).
Gills. Dorsal surface of gill plate I yellowish and of gill plates II – VII greyish on anterior half, brownish on posterior half. Ventral margin of all gill plates yellowish brown, sometimes pinkish. Projection on gill plate III well developed (Fig. 4 H, arrow). Gill plate VII narrow (in natural position of ventral view, Figs 3 J, 4 J). Dorsal margin of gill plates IV – VII with more or less developed papillae; best expressed on gill plates VI – VII (Fig. 4 I).
Cerci. Yellowish brown, basally darkened.
Description of male imago.
General coloration yellowish brown with dark brown maculation (Fig. 5 A). Body length 11.5–13.0 mm (n = 2); length of cerci approximately 2 × body length. Length of fore wings 14.0– 15.3 mm, hind wings 4.5–5.1 mm.
Head. Frons yellowish brown; frontal fold dark brown. Antennae yellowish; scapus and pedicellus darkened. Ocelli basally blackish, apically whitish. Compound eyes greyish brown, basally darkened (Fig. 5 B, C). Compound eyes not touching each other (distance between eyes 0.10–0.66 of median ocellus; n = 3) or touching each other (n = 1).
Thorax. Pronotum dark brown; meso- and metathorax yellowish brown with dark brown maculation. Dorsal surface of mesothorax yellowish brown, median longitudinal suture darkened. Mesothoratic fucasternum yellowish brown to brown. Metathorax with blunt posteromedian projection.
Wing membrane colorless. Veins dark brown, basally paler. Pterostigmatic area cloudy, with simple cross veins. Costal brace dark brown (Fig. 5 A). Hind wings with short triangular costal projection.
Femora basally and apically darkened, median spot present. Tibiae basally darkened; claws dark brown (Fig. 5 A, G). Fore legs darker than middle and hind legs. One claw blunt, one claw pointed.
Abdomen. Color pattern of abdominal terga as described in larva. Tergum X with median macula (Fig. 5 D). Lateral margins with oblique stripe-like maculae on terga I – IX extending dorso-posteriorly, forming transversal stripe-like macula along posterior margin of terga (Fig. 5 D, E). Abdominal sterna with narrow triangular maculae (Fig. 5 F). Styliger yellowish brown; medially slightly convex and sparsely covered by hair-like setae (Fig. 5 H, J). Forceps brown or yellowish, apically paler. Penis lobes brown and basally paler or yellowish, with shallow medio-apical notch (Fig. 5 H, J, arrow), and short spine-like setae on interior edges. Titillators well developed and apically serrated (Fig. 5 H, I). Titillators reach 0.30–0.44 of respective penis lobe length.
Cerci. Yellowish, basally darkened.
Description of female imago.
General coloration yellowish brown with dark brown maculation (Fig. 6 A). Body length 13.0– 15.5 mm (n = 2); length of cerci 2.3 × body length. Length of fore wings 18.2–19.5 mm, hind wings 5.6–6.3 mm.
Head. Frons yellowish brown; frontal fold brownish. Antennae yellowish; scapus and pedicellus darkened. Ocelli basally blackish, apically whitish. Eyes greyish (Fig. 6 B, C).
Thorax. Coloration as described in male imago. Wing membrane colorless (area around bullae sometimes darkened; Fig. 6 A). Veins dark brown, basally paler. Pterostigmatic area cloudy, with mostly simple cross veins. Costal brace dark brown. Hind wings with short triangular costal projection. Coloration of legs as in male imago.
Abdomen. Coloration pattern of abdominal terga and sterna as in male imago (Fig. 6 D – F). Subgenital plate apically narrowed, posterior margin rounded or slightly concave (Fig. 6 G – I). Subanal plate with shallow U-shaped median emargination.
Description of eggs.
Oval shaped, dimensions approximately 188 × 101 μm (average values from 6 eggs). Chorionic surface slightly granulated (Fig. 6 K), without distinct structures. One or two visible micropyle, shallow and rounded, located in subequatorial position (~ 12.5 μm in width) (Fig. 6 J, K).
Main morphological diagnostics of larva.
i) abdominal sterna with more or less defined triangular maculae (Fig. 3 K – N), ii) coloration of abdominal terga as on Fig. 3 F, G, iii) femora with median spot (Fig. 3 H, I), iv) gill plates VII narrow (in natural position from ventral view; Figs 3 J, 4 J), v) tergum X with short posterolateral projections (Fig. 4 L, arrow), vi) abdominal terga and dorsal surface of femora with rounded spatulate setae (Fig. 4 D – F); denticles along posterior margin of abdominal terga dense, irregular and pointed (Fig. 4 F).
Main morphological diagnostics of imago.
i) abdominal sterna with narrow triangular maculae (Figs 5 F, 6 F), ii) coloration of abdominal terga as on Figs 5 D, E, 6 D, E, iii) femora with median spot (Fig. 5 G), iv) wing membrane colourless (Figs 5 A, 6 A) (area of bullae sometimes darkened in female), v) subgenital plate of female rounded or slightly concave (Fig. 6 G – I), vi) subanal plate with shallow median emargination (Fig. 6 H, I), vii) penis lobes not apically widened, with shallow medio-apical notch (Fig. 5 J, arrow), viii) titillators well developed, apically serrated, reaching to 0.30–0.44 of penis lobes in length (Fig. 5 H, J).
Morphological affinities.
Larva. Epeorus (C.) himalayensis sp. nov. is characterised by more or less defined triangular maculae on the abdominal sterna (Fig. 3 K – M). This feature distinguishes E. (C.) himalayensis sp. nov. from E. (C.) guttatus, with a pair of oblique stripes and a large median macula (Fig. 13 H), and E. (C.) extraordinarius, with a longitudinal reddish-brown median macula (Chen et al. 2010). The triangular maculae on abdominal sterna of E. (C.) himalayensis sp. nov. may be narrowed (Fig. 3 N). Similar oblique stripes are present in E. (C.) lanceolatus sp. nov. (Fig. 7 F) and E. (C.) lineatus sp. nov. (Fig. 10 Q). E. (C.) himalayensis sp. nov. can be distinguished from these species based on rounded spatulate setae on abdominal terga, which are lanceolate in E. (C.) lanceolatus sp. nov. (Fig. 8 E, F) and elongated spatulate in E. (C.) lineatus sp. nov. (Fig. 11 E, F). In addition, E. (C.) himalayensis sp. nov. differs from the latter species by the absence of a median longitudinal line on abdominal sterna (or posteromedian macula; Fig. 10 N – Q). The combination of all morphological characters that distinguish E. (C.) himalayensis sp. nov. from both related species are given in the section “ Main morphological diagnostics of the larva ”.
Three other species occur within the eastern part of (E.) Caucasiron range (Fig. 1), which may belong to E. (Caucasiron) based on the morphology of larvae. Of these, E. suspicatus possess oblique stripes on abdominal sterna (Fig. 15 I). However, this species has sparse larger denticles separated by shorter denticles along the posterior margin of abdominal terga (Fig. 16 F), in contrast to dense, irregular, and pointed denticles (Fig. 4 F) in E. (C.) himalayensis sp. nov. Denticulation along abdominal terga separates E. (C.) himalayensis sp. nov. also from E. psi, with basally denticulate spines and shorter denticles (Fig. 18 F). Additionally, E. (C.) himalayensis sp. nov. differs by a short dorso-apical projection on femora (Fig. 3 H, I) from E. psi with an elongate and pointed dorso-apical projection on femora (Figs 17 F, 18 M).
Morphological characters separating E. kapurkripalanorum from E. (C.) himalayensis sp. nov. are given in the section “ Remarks on Iron paraguttatus (Braasch, 1983) and E. kapurkripalanorum (Braasch, 1983) ”. Considering E. (Caucasiron) species from the western part of the area, E. (C.) himalayensis sp. nov. can be easily distinguished by the shape of setae on abdominal terga. It is characterised by rounded spatulate setae, while the extralimital species have fine or basally widened hair-like setae (Hrivniak et al. 2020 b).
Imago. In the eastern part of E. (Caucasiron) area, adults of four species have been described so far, namely E. (C.) guttatus (male and female), E. (C.) extraordinarius (male and female), E. psi (male and female) and E. (C.) lanceolatus sp. nov. (female). E. (C.) himalayensis sp. nov. can be distinguished from them by the colouration pattern of abdominal sterna, each consisting of a narrow triangular macula (Fig. 6 F). This is in contrast to E. (C.) guttatus with a pair of oblique stripes and large median macula (Kluge 2015), E. (C.) extraordinarius with a longitudinal reddish-brown median macula (Chen et al. 2010) and E. (C.) lanceolatus sp. nov. with fine, slightly curved oblique stripes (Fig. 9 F). From the latter species, E. (C.) himalayensis sp. nov. can be separated also by a shallow emargination on the posterior margin of subanal plate in female imago (Fig. 6 G – I), which contrasts with the straight posterior margin in E. (C.) lanceolatus sp. nov. (Fig. 9 H, I).
Based on male genitalia, E. (C.) himalayensis sp. nov. differs from E. (C.) guttatus by longer titillators, reaching at least 1 / 3 of the penis lobes (Fig. 5 H, J), in contrast to short titillators not exceeding styliger in E. (C.) guttatus (Kluge 2015). The shape of penis lobes with a shallow medio-apical notch allows E. (C.) himalayensis sp. nov. to be distinguished from E. psi, which has apically bifurcated penis lobes with extended latero-apical tip (Eaton 1883–1888; Braasch 2006 b).
Among the extralimital species, E. (C.) nigripilosus and E. (C.) caucasicus show similar coloration pattern of abdominal sterna. Epeorus (C.) himalayensis sp. nov. can be distinguished from them by relatively narrow penis lobes with a shallow medio-apical notch, because both species have apically widened penis lobes and a deeper medio-apical notch (Braasch 1979).
description: Published as part of Hrivniak, Ľuboš, Sroka, Pavel, Godunko, Roman J., Martynov, Alexander V., Palatov, Dmitry M. & Bojková, Jindřiška, 2025, Discovering diversity of Central Asian and Himalayan Epeorus (Caucasiron) mayflies (Ephemeroptera, Heptageniidae) using DNA barcoding and morphology, pp. 89-125 in ZooKeys 1234 on pages 89-125, DOI: 10.3897/zookeys.1234.141196