Epeorus (Caucasiron) lineatus Hrivniak & Sroka, 2025

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, ZooKeys 1234, pp. 89-125 : 89-125

Epeorus (Caucasiron) lineatus Hrivniak & Sroka sp. nov.

Figs 10 , 11

Type material.

Holotype: • female larva: India: Uttarakhand Pradesh, vicinity of Badrinath town, Rishi Ganga River, right tributary of Alaknanda River , 3141 m a. s. l.; 30°44.44800'N, 79°29.34600'E; (codes: IND 2018 / 9; 41 Gang); 12–13.05. 2018, Martynov A. V., Palatov D. M. leg. Paratypes: • 27 larvae (barcoded specimens: L 39, SP 31, SP 32; three larvae mounted on slide): same data as holotype . • 5 larvae (barcoded specimens: IN 5 - mounted on slide, SP 21, SP 23): 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. • 1 larva (barcoded specimen: GU 2 - mounted on slide): Tajikistan: Gorno-Badakhshan Autonomous Region, Roshtqal’a District, left tributary of Badamdara River , 3070 m a. s. l.; 37°07.70617N’, 071°50.52000'E (code: 252 Tj); 30. 06. 2016, Palatov D. M. leg.

Etymology.

The species name lineatus (Latin) refers to a median line on abdominal sterna characteristic for larvae.

Description of larva.

General coloration yellowish brown with dark brown to blackish maculation (Fig. 10 ). Body length of late-instar larva unknown. Maximum body length of examined larvae 14.0 mm (female), 9.30 mm (male). Length of cerci ~ 1.2 × body length.

Head. Shape trapezoidal (Fig. 10 D, E ). Head width / length ratio: 1.49–1.56 (female; n = 6), 1.50–1.57 (male; n = 2). Coloration pattern of dorsal surface consists of: i) paired stripe-like and rounded maculae along epicranial suture, ii) pair of triangular (or blurred) maculae 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 or blurred macula between ocelli, vi) scattered smaller maculae ventrally to median ocellus. Antennae yellowish brown, scapus and pedicellus darkened. Dorsal surface covered with elongated spatulate setae (as on abdominal terga; Fig. 11 E ), fine hair-like setae and stick-like setae. Sparse longer and fine hair-like setae located posteriorly to eyes.

Mouthparts. Labrum (Fig. 11 A ) widened anteriorly; anterior margin slightly rounded or nearly straight. Lateral angles rounded. Dorsal surface sparsely covered with setae of different size, 5–6 longer bristle-like setae located antero-medially, and two bristles antero-laterally (Fig. 11 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 5–9 setae of various size (Fig. 11 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. 11 B ), right inner incisor bifurcated (Fig. 11 C ).

Thorax. Prothorax anteriorly narrowed, lateral edges slightly rounded. Metanotum with small blunt posteromedian projection. Dorsal surface covered with hair-like setae, stick-like setae and elongated spatulate setae (as on abdominal terga and head); sparse longer, hair-like setae along pro-, meso-, and metanotal suture.

Legs. Coloration as on Fig. 10 F . Femora with medial 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 rounded (sporadically apically narrowed) spatulate setae (Fig. 11 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 2–3 denticles.

Abdominal terga. Colour pattern of abdominal terga consists of transversal stripe along anterior margin of terga I – IX (X) medially extending to: i) triangular, rounded, or anteriorly and posteriorly widened macula on terga II – IV; and ii) triangular or T-shaped macula on terga V – IX (Fig. 10 I – M ). Lateral margins with oblique stripe-like maculae on terga I – IX, sometimes dorso-posteriorly extended. Denticles along posterior margin on terga dense, irregular, and pointed (Fig. 11 F ). Surface of terga covered with hair-like setae, stick-like setae, and elongated (sporadically rounded) spatulate setae (Fig. 11 E, F ) (dominantly rounded spatulate setae can be present in younger instars). Tergum X with well-developed posterolateral projections (Fig. 11 L , arrow). Terga with longitudinal median row of hair-like setae. More or less developed posteromedian spine (most expressed on terga VII – IX (Fig. 11 M, N ). Posteromedian tergal spine observed only in larvae of BL 4.6–11.2 mm (n = 22; barcoded specimens SP 21, SP 31, L 39, SP 23, IN 5), not observed in larger larvae of BL 11.2–14.0 (n = 5; barcoded specimens: GU 2, SP 32).

Abdominal sterna. Yellowish, with a pattern consisting of oblique stripes and median line extending from anterior to posterior margin (Fig. 10 N – Q ). Median line often posteriorly widened (Fig. 11 N ) or reduced to posteromedian macula Fig. 11 P, Q , arrows). Sternum IX of female apically narrowed, with V-shaped median emargination, and numerous hair-like setae (Fig. 11 O ).

Gills. Dorsal surface of gill plate I yellowish; of gill plates II – VII brownish. Ventral margin of all gill plates yellowish. Projection of gill plate III well-developed (Fig. 11 H , arrow). Gill plate VII wide (in natural position of ventral view, Figs 10 G, H , 11 K ). Dorsal margin of gill plates (III) IV – VII with more or less developed papillae; best expressed on gill plates VI and VII (Fig. 11 I ).

Cerci. Yellowish brown, basally darkened.

Imagoes and eggs.

Unknown.

Main morphological diagnostics of the larva.

i) abdominal sterna with oblique stripes and more or less developed median line (Fig. 10 N – Q ), ii) coloration of abdominal terga as on Fig. 10 I – M, iii ) femora with median spot (Fig. 10 F ), iv) gill plates VII wide (in natural position from ventral view; Figs 10 G, H , 11 K ), v) tergum X with well-developed posterolateral projections (Fig. 11 L , arrow), vi) abdominal terga with elongated (sporadically rounded) spatulate setae (Fig. 11 E, F ), vii) dorsal surface of femora with rounded spatulate setae (Fig. 11 D ), viii) denticles along posterior margin on terga dense, irregular and pointed (Fig. 11 F ).

Morphological affinities.

Larva. Based on the coloration pattern of abdominal sterna consisting of oblique stripes and more or less developed longitudinal median line, E. (C.) lineatus sp. nov. can be distinguished from E. (C.) extraordinarius , with a longitudinal reddish brown median macula ( Chen et al. 2010) and E. (C.) himalayensis sp. nov., with more or less defined triangular maculae (Fig. 3 K – N ). In addition, E. (C.) lineatus sp. nov. differs from the latter species by elongated spatulate setae on abdominal terga (Fig. 11 E, F ) and wide shape of gill plates VII (Figs 10 G, H , 11 K ), in contrast to rounded spatulate setae and narrow gill plates VII in E. (C.) himalayensis sp. nov. (Figs 3 J , 4 J ).

Elongated spatulate setae on abdominal terga separate E. (C.) lineatus sp. nov. from E. (C.) lanceolatus sp. nov., with lanceolate setae on abdominal terga (Fig. 8 E ). Other characters distinguishing E. (C.) lineatus sp. nov. from E. (C.) himalayensis sp. nov. and E. (C.) lanceolatus sp. nov. are given in the section “ Main morphological diagnostics of the larva ”.

Epeorus (C.) lineatus sp. nov. is most similar to Central Asian E. (C.) guttatus . Both species possess elongated spatulate setae on the dorsal margin of abdominal terga, well-developed posterolateral projection on tergum X, wide gill plates VII and similar coloration of abdominal terga and legs. Epeorus (C.) lineatus sp. nov. can be distinguished by the presence of more or less developed longitudinal median line on abdominal sterna (Fig. 10 N – Q ), in contrast to E. (C.) guttatus with large median macula (Fig. 13 H ). A longitudinal median line in E. (C.) lineatus sp. nov. is sometimes posteriorly widened (Fig. 10 N ). When it is pronounced, reaching oblique stripes, the pattern may resemble that of E. (C.) guttatus . This was observed in a specimen collected in Tajikistan (barcoded specimen: GU 2).

Epeorus (C.) lineatus sp. nov. differs from other Epeorus species, which could represent the subgenus Caucasiron based on larval morphology (Fig. 1 ), by dense, irregular, and pointed denticles along posterior margin of abdominal terga (Fig. 11 F ). Epeorus suspicatus possesses sparse larger denticles separated by shorter denticles (Fig. 16 F ) and E. psi basally denticulate spines and short denticles (Fig. 18 F ). The latter species additionally differs by a long and pointed dorso-apical projection of femora (Figs 17 F , 18 M ). Morphological diagnostics of E. kapurkripalanorum are given in the section “ Remarks on Iron paraguttatus (Braasch, 1983) and E. kapurkripalanorum (Braasch, 1983) ”.

Epeorus (C.) lineatus sp. nov. differs from all extralimital species of the subgenus Caucasiron by the presence of spatulate setae on abdominal terga, in contrast to fine or basally widened hair-like setae present in E. (Caucasiron) from the western part of its range ( Hrivniak et al. 2020 b).

Figures

Figure 1. Distribution of studied Epeorus spp. across Asian mountains. Triangles refer to localities in the literature; our sampling sites are marked with red dots. A species name marked with an asterisk indicates the unclear systematic position of the species within the genus Epeorus. Dashed line represents the frame of the detailed map in Fig. 2. Boundaries of mountain ranges were adopted from Snethlage et al. (2022).

Figure 3. Epeorus (Caucasiron) himalayensis sp. nov., larva A habitus in dorsal view B habitus in ventral view C habitus in lateral view D head of male in dorsal view E head of female in dorsal view F, G coloration of abdominal terga H, I middle leg in dorsal view J distal part of abdomen in ventral view K – M coloration of abdominal sterna.

Figure 4. Epeorus (Caucasiron) himalayensis sp. nov., larva A labrum, left half in dorsal view, right half in ventral view (black dots correspond to setae along antero-lateral margin) B incisors of left mandible C incisors of right mandible (both flattened on slide; dashed polygons correspond to area covered by setae) D setae on dorsal surface of femora E setae on surface of tergum VII F surface and posterior margin of abdominal tergum VII G gill I H gill III (arrow shows projection on costal margin) I gill plate VI in dorsal view J gill plate VII in ventral view K gill VII (flattened on slide) L abdominal segments VIII – X in lateral view (arrow shows posterolateral projection of tergum X) M sternum IX of female. Drawn from late instar larvae and last instar larval exuvium.

Figure 8. Epeorus (Caucasiron) lanceolatus sp. nov., larva A labrum, left half in dorsal view, right half in ventral view (black dots correspond to setae along antero-lateral margin) B incisors of left mandible C incisors of right mandible (both flattened on slide; dashed polygons correspond to area covered by setae) D setae on dorsal surface of femora E setae on surface of tergum VII F surface and posterior margin of abdominal tergum VII (holotype) G gill I H gill III (arrow shows projection on costal margin) I gill plate VI in dorsal view J gill VII (flattened on slide) K gill plate VII in ventral view L, M abdominal segments VIII – X in lateral view (arrow shows posterolateral projection of tergum X) N sternum IX of female. Drawn from late instar larva and last instar larval exuvium.

Figure 10. Epeorus (Caucasiron) lineatus sp. nov., larva A habitus in dorsal view B habitus in ventral view C habitus in lateral view D head of male in dorsal view E head of female in dorsal view F middle leg in dorsal view G, H distal part of abdomen in ventral view I – M coloration of abdominal terga N – Q coloration of abdominal sterna II – VI.

Figure 11. Epeorus (Caucasiron) lineatus sp. nov., larva A labrum, left half in dorsal view, right half in ventral view (black dots correspond to setae along antero-lateral margin) B incisors of left mandible C incisors of right mandible (both flattened on slide; dashed polygons correspond to area covered by setae) D setae on dorsal surface of femora E setae on surface of tergum VII (drawn from late-instar larva) F surface and posterior margin of abdominal tergum VII G gill I H gill III (arrow shows projection on costal margin) I gill plate VI in dorsal view J gill plate VII (flattened on slide) K gill plate VII in ventral view L abdominal segments VIII – X in lateral view (arrow shows posterolateral projection of tergum X) M abdominal terga VIII – X with short spines (arrows) N abdominal terga VIII – X with well-developed spines O sternum IX of female. Drawn from late instar larvae.

Figure 13. Epeorus (Caucasiron) guttatus, larva A habitus in dorsal view B habitus in ventral view C habitus in lateral view D head of male in dorsal view E head of female in dorsal view F, G coloration of abdominal terga H coloration of abdominal sterna II – VI I middle leg in dorsal view J distal part of abdomen in ventral view.

Figure 16. Epeorus (Caucasiron?) suspicatus, larva A labrum, left half in dorsal view, right half in ventral view (black dots correspond to setae along antero-lateral margin) B incisors of left mandible C incisors of right mandible (both flattened on slide; dashed polygons correspond to area covered by setae) D setae on dorsal surface of femora E setae on surface of tergum VII F surface and posterior margin of abdominal tergum VII G gill I H gill III (arrow shows projection on costal margin) I gill plate VI in dorsal view J gill plate VII (flattened on slide) K gill plate VII in ventral view L abdominal segments VIII – X in lateral view (arrow shows indistinct posterolateral projection of tergum X) M sternum IX of female. Drawn from late instar larvae.

Figure 17. Epeorus (Caucasiron?) psi, larva A habitus in dorsal view B habitus in ventral view C habitus in lateral view D head of male in dorsal view E head of female in dorsal view F legs in dorsal view (arrows point to elongated and pointed dorso-apical projections) G coloration of abdominal terga H coloration of abdominal sterna II – VI I distal part of abdomen in ventral view.

Figure 18. Epeorus (Caucasiron?) psi, larva A labrum, left half in dorsal view, right half in ventral view (black dots correspond to setae along antero-lateral margin) B incisors of left mandible C incisors of right mandible (both flattened on slide; dashed polygons correspond to area covered by setae) D setae on dorsal surface of femora E setae on surface of tergum VII F surface and posterior margin of abdominal tergum VII G gill I H gill III (arrow shows projection on costal margin) I gill plate VI in dorsal view J gill plate VII in ventral view K gill plate VII (flattened on slide) L abdominal segments VIII – X in lateral view (arrow shows posterolateral projection of tergum X) M detail of dorso-apical projection of femora (middle leg) N sternum IX of female. Drawn from late instar larvae.