Epeorus (Caucasiron) abditus Hrivniak & Sroka, 2024

Hrivniak, Ľuboš, Sroka, Pavel, Türkmen, Gencer, Martynov, Alexander V. & Bojková, Jindřiška, 2024, Integrative delimitation of a new Epeorus (Caucasiron) (Ephemeroptera, Heptageniidae) from the Caucasus with a supplement to the identification guide of Caucasian and Irano-Anatolian species, ZooKeys 1214, pp. 265-279 : 265-279

publication ID	https://doi.org/ 10.3897/zookeys.1214.131266
publication LSID	lsid:zoobank.org:pub:7D4C62C3-BD1C-482E-8116-D87EC8148619
DOI	https://doi.org/10.5281/zenodo.13910122
persistent identifier	https://treatment.plazi.org/id/AF0C3D08-A97C-483C-A766-9B3F9CFE6113
taxon LSID	lsid:zoobank.org:act:AF0C3D08-A97C-483C-A766-9B3F9CFE6113
treatment provided by	ZooKeys by Pensoft
scientific name	Epeorus (Caucasiron) abditus Hrivniak & Sroka
status	sp. nov.

Treatment

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

Figs 4 View Figure 4 , 5 View Figure 5

Type material.

Holotype • female larva ( GB: PP 987170 ), Türkiye: Artvin Province, Camili Village , unnamed mountain stream, 1599 m a. s. l.; 41°24'04"N, 42°24'04"E; code: CAM 6, 25. 7. 2016, G. Türkmen leg. GoogleMaps

Paratypes • 1 larva (mounted on slide), same data as holotype GoogleMaps • 1 larva ( GB: PP 987171 ; mounted on slide), Georgia: Adjara, Kobuleti district, vicinity of Khino (Didvake) village, Kintrishi River , 792 m a. s. l.; 41°43'01"N, 42°02'41"E; code: No 6, 19. 4. 2013, A. V. Martynov leg GoogleMaps • 1 larva ( GB: PP 987168 , mouthparts mounted on slide), Georgia: Kakheti Province, South of Alazani Pass, Stori River , 1514 m a. s. l.; 42°14'35.1"N, 45°29'44.5"E; code GEO 60 / 2019, 3. 5. 2019; Ľ. Hrivniak leg GoogleMaps • 1 larva, Russia: Kabardino-Balkaria, vicinity of Terskol village, left tributary of Baksan River , 2192 m a. s. l.; 43°14'31"N, 42°33'49"E; 19. 5. 2013, V. V. Martynov leg GoogleMaps • 2 larvae (one barcoded, GB: PP 987169 ), Russia: Kabardino-Balkaria, vicinity of Tyrnyauz village, right tributary of Baksan River , 1904 m a. s. l., 43°21'N, 42°52'E; 19. 5. 2013, V. V. Martynov leg. GoogleMaps

Type material is deposited in IECA.

Etymology.

The species name abditus (Latin) means hidden. It refers to rare distribution and morphological similarity with related species.

Distribution and habitat preferences of larvae.

Epeorus (Caucasiron) abditus sp. nov. has relatively wide distribution in the Caucasus region but appears to be relatively rare due to low number of specimens obtained by extensive sampling. They were found in the Pontic Mountains and the Lesser Caucasus (northeast Türkiye and southwest Georgia), and the central ( Russia: Kabardino-Balkaria) and eastern ( Georgia: Kakheti) parts of the Greater Caucasus (Fig. 1 View Figure 1 ). The larvae were found in low abundance in cold and clear streams and rivers between 792 and 2192 m a. s. l. on stony bed substrate in turbulent flow (Fig. 3 View Figure 3 ). They were not recorded in urban and agricultural areas within the region, where many localities were investigated. Larvae co-occurred with E. (C.) znojkoi , E. (C.) alpestris (Braasch, 1979) , E. (C.) magnus .

Description of larva.

General colouration of larvae yellowish brown with dark brown maculation. Body length of late instar larvae: ca 13.3 mm (female), 11.1–11.25 mm (male). Length of cerci approximately 1.2 × body length.

Head. Shape oval to trapezoidal. Anterior and lateral margin rounded, posterior margin rounded in female (Fig. 4 E View Figure 4 ) and slightly rounded in male (Fig. 4 D View Figure 4 ). Head dimensions of late instar larvae: length ca 4.5 mm, width ca 3.2 mm in female; length ca 4.05 mm, width 2.75–2.8 mm in male. Head width / length ratio: 1.46–1.48 in female; 1.46–1.51 in male.

Colouration of head: dorsal surface with pair of elongated maculae located along epicranial suture; pale stripes extending from lateral ocelli to lateral edges of head; blurred (or rectangular) macula between ocelli; rounded maculae anterolateral of lateral ocelli; blurred (or triangular) maculae near inner edges of compound eyes; pair of stripes (or scattered smaller maculae) located anteriorly from median ocellus (Fig. 4 D, E View Figure 4 ). Compound eyes grey to brownish to black. Ocelli blackish. Antennae yellowish brown, scapus and pedicellus darkened. Hair-like setae along anterior margin of head extend to lateral margins. Dorsal surface of head covered with fine hair-like setae and sparsely distributed stick-like setae. Sparse longer and fine hair-like setae located posteriorly to eyes.

Mouthparts. Labrum (Fig. 5 A View Figure 5 ) widened anteriorly, with anterior margin slightly rounded or nearly straight (in dorsal view), lateral angles rounded. Dorsal surface (Fig. 5 A View Figure 5 , left) sparsely covered with hair-like setae and short bristle-like setae; 5–6 longer bristle-like setae located antero-medially and two antero-laterally. Epipharynx with longer, shortly plumose bristles situated along lateral to anterior margin (Fig. 5 A View Figure 5 , right; range of setation figured as large black dots), and brush of fine hair-like setae medially (not figured); ventral surface with group of 10–16 setae of various size located medio-posteriorly. Outer incisors of both mandibles with three apical teeth (Fig. 5 B, C View Figure 5 ). Inner incisor of left mandible with three apical teeth, right inner incisor bifurcated. Outer edge of both mandibular incisors with numerous setae (range of setae marked with dashed polygons).

Thorax. Pronotum anteriorly narrowed, lateral edges slightly curved. Metanotum with slight postero-medial projection. Dorsal surface with dark brown maculation as on Fig. 4 A View Figure 4 and covered with fine, hair-like setae (as on abdominal terga and head); sparse longer, hair-like setae along pro-, meso- and metanotal suture.

Legs. Colour pattern of femora as on Fig. 4 F View Figure 4 . Femora without medial hypodermal spot. Femora apically slightly darkened; patella-tibial suture darkened; tarsi proximally and distally darkened. Dorsal surface of femora covered by short (sporadically elongated) apically rounded spatulate setae (Fig. 5 D View Figure 5 ). Dorsal margin of tibiae and tarsi with row of long setae; ventral margin of both with short distally accumulated spine-like setae. Tarsal claws with 3–4 denticles.

Abdominal terga. Colour pattern of abdominal terga consists of transversal stripe along anterior margin of terga I – IX, medially extending to: i) large median triangular macula on terga II – III (IV), and ii) triangular or T-shaped macula on terga V – IX (medial macula on tergum VIII and IX often widened). Median macula on terga V – VII surrounded by pale area (Fig. 4 G View Figure 4 ). Tergum X without distinct maculation. Lateral margin of terga I – IX with oblique macula. Denticles along posterior margin on terga strongly sclerotised, irregular and pointed (Fig. 5 E View Figure 5 ). Surface of terga covered with hair-like setae and sparsely with stick-like setae. Tergum X with short postero-lateral projections (Fig. 5 J, K View Figure 5 ). Longitudinal medial row of hair-like setae along abdominal terga present.

Abdominal sterna. Yellowish, with colouration pattern on sterna I – VIII consisting of rounded median macula (Fig. 4 H View Figure 4 , arrow). In more pigmented specimens, median macula with paired pale spots located medio-posteriorly. Rounded median macula often poorly expressed and only medio-posterior edge of sterna is slightly pigmented (Fig. 4 I View Figure 4 , arrow). Colouration pattern sporadically restricted to sterna I and II or absent. Sternum IX of female with V-shaped median emargination and surface covered by setae centrally (Fig. 5 L View Figure 5 ).

Gills. Dorsal surface of gill plate I yellowish; of gill plates II – VII greyish on anterior half, brownish on posterior half. Ventral margin of all gill plates yellowish. Costal projection on gill plate III well-developed (Fig. 5 G View Figure 5 , arrow). Gill plate VII wide (in natural position of ventral view; Figs 4 J View Figure 4 , 5 H, I View Figure 5 ).

Cerci. Yellowish brown, basally darkened.

Subimagoes, imagoes, and eggs.

Unknown.

Morphological diagnostics of larvae.

Epeorus (Caucasiron) abditus sp. nov. can be distinguished by the combination of the following morphological characters: i) femora without median spot (Fig. 4 F View Figure 4 ); ii) abdominal sterna with circular median macula as on Fig. 4 H View Figure 4 (colouration may be restricted to medio-posterior part of sterna as on Fig. 4 I View Figure 4 ); iii) abdominal terga V – VII with triangular or T-shaped macula surrounded by pale area (Fig. 4 G View Figure 4 ); iv) tergum X with short postero-lateral projection (Fig. 5 J, K View Figure 5 , arrow); v) surface of abdominal terga with hair-like setae (Fig. 5 E View Figure 5 ); vi) shape of gill plates VII wide (in natural position from ventral view, Figs 4 J View Figure 4 ; 5 H, I View Figure 5 ).

Morphological affinities.

Epeorus (Caucasiron) abditus sp. nov. is similar to several species from the Caucasus and neighbouring Mediterranean and Irano-Anatolian ranges, namely E. (C.) alpestris (distributed in the Greater Caucasus), E. (C.) alborzicus Hrivniak & Sroka, 2020 (Alborz Mountains), and E. (C.) bicolliculatus Hrivniak, 2017 (Pontic Mountains, Lesser and Greater Caucasus). All of them possess abdominal sterna with a rounded median macula and femora without median spot ( Hrivniak et al. 2020 b).

Epeorus (C.) alpestris can be distinguished from E. (C.) abditus sp. nov. by the absence of postero-lateral projections on the tergum X ( Hrivniak et al. 2020 b, fig. 17 L) present in E. (C.) abditus sp. nov. (Fig. 5 J, K View Figure 5 , arrow). Additionally, the rounded maculae on abdominal sterna are always present in E. (C.) alpestris ( Hrivniak et al. 2020 b, fig. 16 I), whereas the colouration pattern of abdominal sterna varies from a well-defined pattern (Fig. 4 H View Figure 4 ) to an indistinct (Fig. 4 I View Figure 4 ) or no pattern in E. (C.) abditus sp. nov. Moreover, Epeorus (C.) alpestris is characterised by typical maculation of abdominal terga ( Hrivniak et al. 2020 b, fig. 16 G, H).

Epeorus (C.) alborzicus possesses abdominal sterna with a large circular medial macula ( Hrivniak et al. 2020 b, fig. 40 L – N) and blurred macula (or a pair of rounded maculae) on tergum II and III ( Hrivniak et al. 2020 b, fig. 40 H, I), in contrast to E. (C.) abditus sp. nov. with relatively small rounded medial macula on abdominal sterna (Fig. 4 H, I View Figure 4 ) and triangular macula on tergum II and III (Fig. 4 G View Figure 4 ).

Epeorus (C.) bicolliculatus differs from E. (C.) abditus sp. nov. by the presence of paired postero-medial protuberances on abdominal terga II – IX ( Hrivniak et al. 2020 b, fig. 34 H) and basally widened setae on the surface of terga ( Hrivniak et al. 2020 b, fig. 35 E) in contrast to basally narrow setae in E. (C.) abditus sp. nov. (Fig. 5 E View Figure 5 ).

The larvae of E. (C.) abditus sp. nov. with weakly pigmented abdominal sterna may be erroneously assigned to E. (C.) magnus (distributed in the Greater and Lesser Caucasus, Pontic and Taurus Mountains). This species differs from E. (C.) abditus sp. nov. by the presence of dense bristle-like setae on the dorsal surface of the labrum ( Hrivniak et al. 2020 b, fig. 11 A) in contrast to sparse and hair-like setae in E. (C.) abditus sp. nov. (Fig. 5 A View Figure 5 ). In addition, E. (C.) magnus often has clearly developed lateral projections on the tergum X ( Hrivniak et al. 2020 b, fig. 11 K – M) in contrast to only short projections in E. (C.) abditus sp. nov. (Fig. 5 J, K View Figure 5 ).

Two species distributed in the western and central Greater Caucasus, namely E. (C.) soldani (Braasch, 1979) and E. (C.) sinitshenkovae (Braasch & Zimmerman, 1979) , have abdominal sterna without or with weakly developed colouration pattern and no femoral spot. Epeorus (C.) soldani can also be easily distinguished from E. (C.) abditus sp. nov. by setae on abdominal terga that are basally widened in the former species ( Hrivniak et al. 2020 b, fig. 20 E) and narrow in the latter (Fig. 5 E View Figure 5 ). Epeorus (C.) sinitshenkovae can be separated by a poorly developed projection on costal margin of gill plates ( Hrivniak et al. 2020 b, fig. 26 G) from E. (C.) abditus sp. nov. bearing a well-developed projection (Fig. 5 G View Figure 5 ). Additionally, E. (C.) sinitshenkovae is characterised by a specific colouration of abdominal terga and femora ( Hrivniak et al. 2020 b, fig. 25 H, F).