Isoperla chereshnevi Teslenko, 2017

Teslenko, Valentina A. & Khamenkova, Elena, 2017, A new species of Isoperla Banks (Plecoptera: Perlodidae) from the northeast of the Russian Far East, Zootaxa 4300 (2), pp. 238-244 : 239-243

Isoperla chereshnevi Teslenko , sp. n.

( Figs. 1 ¯19)

Material examined. Holotype male: Northeast of the Russian Far East , northern coast of the Sea of Okhotsk , Magadanskaya Oblast, Lankovaya River, Ola River Basin, N 59°40.359’ E 151°26.071’, 2.07.2016, coll. E. Khamenkova. Paratypes: same data and location as holotype, 2 males and 1 female (one mounted on a slide), coll. E. Khamenkova ; 3 larvae, the same location, 1–2.07.2016, coll. E. Khamenkova ; 1 male, Ola River , 22.07.1974, coll. I. Zasypkina ; 1 larvae, Ola River , 6.07.1984, coll. I. Zasypkina ; 1 male, Bolshaya Garmanda River , 16.07.1984, coll. I. Zasypkina.

Etymology. The species is named in honor of the outstanding hydrobiologist, Igor Alexandrovich Chereshnev, who has made significant contributions to the knowledge of the systematics, biogeography, and biology of the freshwater fishes northeast of the Russian Far East.

Description. Male. Macropterous; forewing length 9.0– 9.4 mm. Body length 8.1–9.1 mm. General body color brown with pale markings dorsally ( Fig. 1 ). Head brown, a tear-shaped interocellar pale spot surrounded anteriorly by inverted V-shaped dark patch with arcuate lateral edges near posterior ocelli and separated from a pale spot on occiput ( Fig. 1 ). In front of dark brown M-line a distinct arrow-shaped brown spot projects onto the clypeus; tentorial pits dark brown, lateral margins of the clypeus pale. Areas between posterior ocelli and the compound eyes are brown. Occiput brown with a pale oval spot medially ( Fig. 1 ). Antenna brown, scape dark brown. Pronotum brown ( Fig. 1 ) with medial pale band slightly widened to posterior margin; anterior and posterior pronotal margins dark brown, lateral margins pale, rugosities X-shaped, raised, dark brown ( Fig. 1 ). Femora medium brown, tibia with narrow dark brown band on proximal ½ ( Fig. 1 ), tarsi dark brown in distal half. Meso- and metanota dark brown with pale patches anteromedially, pale patch on metanota small ( Fig. 1 ). Wings transparent, veins brown. Terga brown, terga 1¯4 with paired pale bands medially divided by brown stripe, tergum 8 dark brown ( Figs. 1, 3 ). Tergum 9 with a pair of pale patches laterally, shallowly depressed along median line with mesal bipartite, medium brown patch, posterior margin with submedial, slightly transversely elongated swellings, covered by fine colorless hairs posterolaterally ( Fig. 3 ). Tergum 10 depressed along median line with a narrow longitudinal pale band and mesal bipartite oval medium brown patches ( Fig. 3 ), posteromesal margin covered with spinulae. Paraprocts short, broadly triangular, heavily sclerotized on outer margin apically; tips bluntly pointed, slightly recurved with scattered short stout setae over dorsal surface on apices ( Figs. 3, 4 ). Cerci brown, terminal segments dark brown; each cercal segment with a single ventral spinule posteriorly. Sterna brown, with light brown medial band on sterna 5¯8 ( Fig. 2 ). Sternum 8 with vesicle, 1.2X as long as wide; evenly rounded and expanded posteriorly, extending to the anterior margin of sternum 9, sternum 9 with medium brown patch anteriorly ( Fig. 2 ). Aedeagus in resting position consists of several membranous folds and lobes covered mainly with tiny dense sharp golden setae with round bases ( Figs. 5 ¯8); dorsal area expanded, leaf-shaped with paired rounded lateral lobes bent down and an unpaired triangular dorsomedial lobe with tapered apex directed oblique upward and forward ( Figs. 6, 7 ); posterodorsal area with a pair of short posterolateral lobes, which look like wavy ribbons in ventral view ( Figs. 5, 7 ); posteromedial area with about 32 tightly packed stout reddish brown spines that are obtuse apically; the bases of spines are bulbous; the height of the bases slightly exceeds the length of the spines ( Fig. 9 ). The stout reddish brown posteromedial spines visible through membrane in ventral view, laterally, appearing as a darkened narrow band inside posteromedial lobe ( Figs. 6, 7 ).

Female. Macropterous, forewing wing length 11.4 mm, body length 11.2 mm. Body coloration and morphology similar to male. Sternum 8 brown, subgenital plate broadly rounded, extending approximately ¼ over sternum 9; posterior margin of subgenital plate with triangular dark brown patch and small medial notch ( Fig. 10 ). Sternum 9 medium brown with a pair of small dark brown patches on the posterolateral margins ( Fig. 10 ). Female contains immature ova.

Larva. Body length: male 8.5–9.2 mm, female 10 mm. Preserved specimens brown with pale markings and pale legs ( Fig. 11 ). Pilosity usual for the genus, head with incomplete transverse occipital spinule row; pronotal, posterior tergal fringes and apical whorl of cercal segments contain relatively short and blunt bristles, a few bristles on posterior pronotal corners much longer than on anterior ones, swimming hairs present on femora, tibiae, metatarsi and distal half of the cerci ( Figs. 11, 16, 17 ). Dorsum of head brown with a contrasting pale pattern ( Fig. 12 ); a pale spot anterior to median ocellus expanding to anterior margin of frontoclypeus; frontoclypeus and lateral frontoclypeal corners brown ( Fig. 12 ); interocellar area with longitudinal diamond-shaped pale spot, lateral branches of M-line pale and distinct, tentorial callosities pale and visible; a small pale spot beyond each posterior ocellus laterally opens along epicranial suture and converges with large round occipital pale spot at inner edge of each eye. Occiput bears a single triangular medial pale spot and pair of unclear lateral pale patches behind the eyes ( Fig. 12 ). Antennae pale, scape medium brown. Pronotum oval with rounded corners, 1.6Χ as long, brown with diffuse median diamond-shaped pale patch; anterior and posterior pronotal margins dark brown, lateral margins pale, lateral fields brown ( Figs. 11, 12 ). Abdominal tergites brown, each with four round pale spots, the paramedial spots partly fused on posterior tergites ( Fig. 11 ), posterior tergal margins with fringe of brownish setae; transverse row of dark pigmented spots hardly seen on all tergites. Ventral surface of abdomen pale, distal segments brownish. Paraprocts brown, cerci pale. Apical half of cerci densely packed with dorsal fringe of silky hairs, length of hairs not exceeding length of the corresponding segment ( Figs. 15 ¯17). Additionally the apical whorl in apical half of cerci bears one long dorsal and one long ventral seta, dorsal seta longer than ventral; the longest dorsal setae may reach approximately ¾ of the length of the corresponding segments ( Figs. 16–17 ).

Lacinia bidentate, triangular ( Fig. 13 ) with shallow notch on inner margin medially bearing about 10 strong marginal setae below subapical tooth; marginal setae continuous to the base, thinner and shorter than beneath the apical and subapical teeth; three long thin hairs arranged near apical and subapical teeth. Galea with thin setae scattered along outer edge, length of galea reaches the base of the apical tooth ( Fig. 13 ). Mandible with 6 pointed teeth and a deep cleft between apical and subapical teeth ( Fig. 14 ).

Diagnosis. Isoperla chereshnevi is superficially similar in general habitus to I. obscura (Zetterstedt, 1840) recorded from the northeast of the Russian Far East from the Kolyma River Basin ( Levanidova & Zhiltzova 1979). However, males of the two species are separable by the shape of the paraprocts, aedeagal armature, and head pattern. The paraprocts of I. chereshnevi are broadly triangular and bear a few short stout spines on the dorsal surface of the strongly sclerotized apices. The posteromedial structure of the aedeagus has stout reddish brown spines and the bases of spines are bulbous and longer than the spines. Additionally, dorsally, the head of I. chereshnevi has brown pigmentation between posterior ocellus and compound eye. The paraprocts of I. obscura are triangular and elongated with acute apices covered with thin setae. The aedeagal armature includes a conspicuous V-shaped row of sharp broadly triangular spines (figs. 9c, d, in Zwick & Surenchorloo 2005). Additionally, the head of I. obscura lacks pigmentation between posterior ocellus and compound eye (fig. 9a in Zwick & Surenchorloo 2005). Females of I. chereshnevi can be separated by a broadly rounded subgenital plate with triangular dark brown patch and small medial notch, whereas, the female of I. obscura has an elongate nearly triangular subgenital plate.

Distribution. Isoperla chereshnevi was collected from the Lankovaya River ( Figs. 18, 19 ), a tributary of the Ola River on the northern coast of the Sea of Okhotsk, Magadanskaya Oblast. The Lankovaya River originates from the montane Kishi Lake and flows for 162 km with a total catchment of 3,270 km ². The Lankovaya River is a typical meandering humic tundra river with low gradient and long pools ( Figs. 18, 19 ). Pink salmon ( Oncorhynchus gorbuscha (Walbaum, 1792)) , chum salmon ( Oncorhynchus keta (Walbaum, 1792)) , and coho salmon ( Oncorhynchus kisutch (Walbaum, 1792)) are important fish species occurring in the river. There are many thermokarst lakes in the floodplain of the river. The Lankovava River valley is wide, bordered by picturesque spurs of the Bilibin Ridge on the north and in the south separated from the Sea of Okhotsk by the low mountains of the Kil Ridge. The new species was also collected in mainstream Ola River and northeast of type locality in the Bol’shaya Garmanda River, Gizhiga Bay of the Sea of Okhotsk. Based on the above records, the emergence period of I. chereshnevi appears to be during the month of July.

Figures

FIGURES 1 – 4. Isoperla chereshnevi sp. n.: 1. Habitus, holotype male, dorsal. 2. Male abdominal tip, ventral. 3. Male abdominal tip, dorsal. 4. Male paraprocts, dorsal. Scale (mm): 4 = 0.1.

FIGURES 5 – 10. Isoperla chereshnevi sp. n.: 5. Aedeagus uneverted, dorsal. Posterodorsal portion with short posterolateral lobes. 6. Aedeagus, lateral. Paired rounded lateral lobes bent down; unpaired a triangular dorsomedial lobe, tapered on apex, directed obliquely upward and forward. 7. Aedeagus, ventral. Paired posterolateral lobes like wavy ribbons; posteromedial structure with stout spines in transparency. 8. Sharp golden setae with round bases. 9. Posteromedial structure of aedeagus, tightly packed stout spines with bulbous basis, ventral. 10. Female, abdominal tip, ventral. Scale (mm): 5 ‾ 9 = 0.1.

FIGURES 11 – 17. Isoperla chereshnevi sp. n., larva: 11. Habitus, dorsal. 12. Head and pronotum, dorsal. 13. Right lacinia, ventral. 14. Right mandible, ventral. 15. Right cercus, basal segments, ventral. 16. Right cercus, middle segments, ventral. 17. Right cercus, apical segments, ventral. Scale (mm): 13 ‾ 14 = 0.1, 15 ‾ 17 = 0.3.

FIGURES 18 – 19. Type locality, Lankovaya River, Magadanskaya Oblast, northeast of the Russian Far East, northern coast of the Sea of Okhotsk.