Metretopus omelkoi, Tiunova, Tatiana M., 2012

Tiunova, Tatiana M., 2012, A new species of Metreletus Demoulin, 1951 from the far eastern region of Russia (Ephemeroptera: Ameletidae), Zootaxa 3349, pp. 31-39 : 31-39

Metretopus omelkoi sp. nov.

( Figs 1 –35)

Material examined. Holotype male imago, RUSSIA, Primorskiy Kray, Ussuriiskii region, Mountain-Taiga Station of Far-Eastern Branch of Russian Academy of Sciences, temporary stream along the road, 4.VI.2011, T. Tiunova. Paratypes: collected together with the holotype: 80 male and 50 female imagines, 15 male and 17 female subimagines, and 60 mature larvae.

Description. Male imago (in alcohol). Length (mm)—body 7.4–9.2; forewings 8.2–9.2; cerci 17.0–19.3. Total color of living imago brown with brightly yellow, blown-up membranous connection in the root of wings and between anepisternum and the posterior arm of the prealar bridge (Fig. 32). After fixing in alcohol, yellow coloring becomes white. Head: upper portion of eyes gray-brown; lower portion dark gray. Eyes contiguous dorsally. Medial and lateral eyes dark brown. Thorax: Pronotum brown with narrow white stripe along the middle part of the posterior margin ( Fig. 1 ). Medioscutum and submedioscutum dark brown; color of median longitudinal suture varies in different specimens from pale to dark brown. Scutellum brown with thin white median stripe. Infrascutellum and parascutellum dark. Posterior scutellar protuberance with light brown spot on the anterior margin. Scutoscutellar impression ranging from light brown at the base to white in the distal region ( Fig. 1 ). Fore legs brown; middle and hind legs from light brown to yellowish with brown joints. Length (mm) of the fore leg segments: femora 1.9–2.3; tibia 1.5–1.9; tarsal segments 0.4–0.6, 0.9–1.2, 0.9–1.2, 0.7–0.9, and 0.4–0.5. Wings hyaline and brownish; all veins brown; pterostigma whitish ( Figs 9–10 ). Abdomen: terga from brownish to brown and translucent; lateral margin of terga dark brown; tergum I dark brown; terga II–III light brown, and IV–VII, grayish; terga II–VII having a wide medial hyaline stripe with a pair of tear-shaped brown spots on the anterior margin; terga VIII–IX brown with a white granular coating and not transparent; terga VIII–IX with median stripe and elongated white spot along the lateral margins; tergum X dark brown with white corners of the anterior region ( Figs 7 , 32). Sterna I–II dark brown; sterna III–VIII from light brown to whitish and translucent with a contrasting middle contour brown spot near the anterior margin; sterna IV–VII, with a pair of brown spots or curved stripes in the distal region ( Fig. 8 ). Styliger and forceps dark brown; middle part of styliger lighter than side; posterior margin with a narrow light band; styliger with a deep and wide posteromedian incision ( Fig. 3 ). At the base of first segment of forceps, on its inner side, there is a pointed protuberance ( Fig. 3 ). Penis lobes light brown in the inner and brown in the external parts with their tops covered with small spines ( Figs 4–5 ); top of penis lobes has a deep notch, which divides it into two unequal parts ( Figs 5–6 ); the inner part is broad and rounded, and the outer part is twice as narrow as the inner and does not reach its apex ( Fig. 2 ). Cerci dark brown with brownish ends.

Female imago. Length (mm)—body 7.5–10.4; forewings 8.3–9.5; cerci 11.0–15.0. Total color of living imago is similar to the male. Thorax: Legs brown; forelegs darker than middle and hind; joints brown. Abdomen: tergum I brown; terga II–VIII dirty gray and translucent without drawing, the lateral edges and corners at the base are dark brown; posterior margin of each terga dark brown; terga IX–X brown, and a diffuse drawing is not clear. Sterna as in the male. Subgeninal plate has a deep and broad depression ( Fig. 11 ). Cerci dark brown.

Male subimago Total color light brown. Wings opaque and translucent. Legs from light yellow to whitish; all joints brown. Terga without drawing and not transparent; posterior margin of each tergum brown (Fig. 33). Sterna light brown with a pattern, as in the male imago. Cerci brown and darker at the base.

Female subimago. Total color light brown. Thorax matt. Wings opaque and translucent. Legs light yellow or whitish; joints brown. Terga light brown; lateral angles of the posterior margin dark brown; posterior margin of each tergum brown. Sterna light brown with a pattern as in the female imago. Cerci dark brown.

Mature larva. Length (mm)—body 7.4–10.0; cerci 3.5–5.7. Head: mostly light brown or brownish; area in front of eyes and ocellus whitish; frontal carina with wide light stripe. Antennae light brown at the base and brown at the ends. Labrum with a deep apical incision; lateral margin dark brown; setae at the anterior margin of labrum like a brush ( Fig. 12 ). Labium light with a narrow almost parallel separation of glossae in middle and divergent to tops; inner edge of the glossae with a strong setae; apical area with numerous irregularly located setae; paraglossae length does not exceed glossae length; third segment of labial palpi brown and well contrasted with other segments ( Figs 14–15 ). Most inner area of the maxilla light, the outer edge, above the maxillary palpi, brown ( Fig. 18 ). Incisor of the mandible 2.5–3 times wider than kinetodontium ( Figs 16–17 ). Thorax: pronotum and mesonotum light brown. Femur of each leg with brown outer and inner edges and light middle part; setae on the dorsal surface of the fore femora short and strong ( Fig. 19 ); tibia light brown; tarsus and claw darker; claw with small denticles near base and a row of greater denticles in middle portion ( Fig. 20 ). Lengths (mm) of leg segments are as follows. Foreleg: femur 1.0–1.2; tibia 0.5–0.6; and tarsus 0.9–1.0. Middle leg: femur 1.0–1.2; tibia 0.5–0.6; and tarsus 0.8–0.9. Hind leg: femur 1.1–1.3; tibia 0.6–0.7; and tarsus 0.8–0.9. Abdomen: terga brown and usually monotonous; lateral lower corners of terga I–VIII dark brown. Sterna from light brown to matter; sterna IV–VIII with brown diamondshaped outline spot in the middle portion of the anterior margin; abdominal sternum 9 in female with deep posteromedian emargination ( Fig. 21 ). Gills long and narrow with a pinkish tinge and conspicuous trachea; gill I is more narrow than the other gills, reaching the posterior margin of tergum III, and its length 4.3 times exceeds it is width ( Fig. 22 ); lengths of gills II–III 3.7 times exceed their width ( Figs 23–24 ); gills IV–V are the same, wider than gills II–III, and their length 3 times exceed their width ( Figs 25–26 ); gill IV slightly shorter and narrower than gills III–V, and its length 3.2 times exceeds its width ( Fig. 27 ); gill VII reaches the end of the last tergum, somewhat shorter and narrower than gill IV, and its length 4.4 times exceeds its width ( Fig. 28 ). Caudally brownish with slightly darkened tips.

Eggs. General form of egg ovate with a length of 286–320 µm and a width of 181–238 µm ( Fig. 29 ). Chorionic surface covered with net-like ribbed structures with mesh diameters 12–16 µm ( Fig. 30 ). Pores or micropiles small, poorly expressed ( Fig. 30–31 ).

Etymology. The species is named in honor of Dr. Mikhail Omelko, who for a long time has been an investigator of moths in Russia.

Distribution and biology. Known from Far-Eastern Russia. Specimens were collected in a temporary stream flowing along the road, with copiously overgrown grass vegetation (Fig. 34). The bottom of the stream is swampy with much silt and residues of half-rotten plants. The water temperature was 11°C (June 4). The larvae were noted only in a 100 meter section of the stream. The quantity of the mature larvae was very high. From June 4 till June 11, there was a mass emergence of subimago from the larvae, and they remained on the grass near the stream (Fig. 33), and the male imagines mass swarmed over the grass and small scrub at a height of not more than 1 meter. The swarming usually began after 4:00 pm and lasted until 8:00 pm. Males in the vertical position slowly rose and fell over the vegetation. The swarming lasted 15–20 minutes; thereafter, the males rested on nearby leaves. After some time, the males took off again. We found a small extension stream nearby and found dead females floating after laying their eggs (Fig. 35). In July, the water in the stream disappeared, and the bottom was overgrown with grass.

Discussion. The male imago of M. omelkoi sp. nov. can be distinguished from M. balcanicus by the following characteristics. The wings of M. balcanicus are yellowish, whereas the wings of M. omelkoi are brownish and hyaline. M. omelkoi has a styliger plate with a deep and wide median incision ( Fig. 3 ), in contrast to M. balcanicus , whose median incision is deep and narrow ( Studemann et al., 1988: Fig. 48). The outer part of the penis lobe of M. balcanicus is long and pointed, reaching the top of the inner part ( Demoulin, 1951: Fig. 5 ); ( Studemann et al., 1988: Figs 45–47)]. In M. omelkoi , the inner part is broad and rounded, and the outer part is twice as narrow as the inner part and does not reach its apex ( Fig. 2 ).

FIGURES. 32. Metreletus omelkoi sp. nov., male imago.

FIGURES. 33. Metreletus omelkoi sp. nov., male subimago.

FIGURES. 34. Biotope: temporary stream flowing along the road.

FIGURES. 35. Females floating after laying eggs.

The larvae of M. omelkoi sp. nov. differ from those of M. micus and M. balcanicus by the size of gill I and the form and ratio of the length to the width of the other gills. In M. omelkoi sp. nov. gill I is long and reaches the posterior margin of tergum III; in contrast to it, in M. micus gill I is small, reaching only the middle part of terga II ( Bajkova, 1976: Fig. 9 ). In M. omelkoi sp. nov., gills II–VII are long and oval, slightly tapering into the posterior margin ( Figs 23–28 ). The ratio of length to width of the gills are as following: gill I—4; gills II and III—3.7; gills IV-V—3; gill VI—3.2; gill VII—4.4. In M. balcanicus gills II–VII are expanded in the distal part, and their trailing edges are blunt ( Demoulin, 1951: Fig. 6 ); ( Ujhelyi, 1960: Fig. 16 ). The ratio of length to width of the gills in this species are as follows: gill I—3.5; gill II—3; gill III—3.8; gill IV—2.7; gill V—2.2; gill VI—2.0; and gill VII—2.6. Thus, gills IV–VII in M. balcanicus are shorter and wider than those of M. omelkoi .

Figures

FIGURES 1 – 11. Metreletus omelkoi sp. nov.: male imago: 1. Mesonotum, dorsal view. 2. Genitalia, lateral view. 3. Sternum IX, styliger and gonostyli. 4. Penis, ventral view. 5. Penis, dorsal view. 6. Penis, lateral view. 7. Abdominal terga. 8. Abdominal sterna. 9. Fore wing. 10. Hind wing. 11. Subgenital plate, female, dorsal view. Scale: Figs 1 – 3 and 9 — 0.5 mm; Figs 4 – 6 and 11 — 0.2 mm; Figs 7 – 8 — 2.0 mm; Fig. 10 — 1.0 mm.

FIGURES 12 – 21. Metreletus omelkoi sp. nov., larva: 12. Labrum, dorsal view. 13. Labrum, ventral view. 14. Labium, dorsal view. 15. Labium, ventral view. 16 – 17. Apices of mandibles, dorsal view: 16 — right mandible, 17 — left mandible. 18. Right maxilla, dorsal view. 19. Femur of fore leg. 20. Claw of fore leg. 21. Abdominal sternum 9 (female). Scale (mm): Figs 12 – 15, 18 – 19 and 21 — 0.5 mm; Figs 16 – 17 and 20 — 0.1 mm.

FIGURES 22 – 28. Metreletus omelkoi sp. nov., gills: 22. Gill I. 23. Gill II. 24. Gill III. 25. Gill IV. 26. Gill V. 27. Gill VI. 28. Gill VII. Scale 0.5 mm.

FIGURES 29 – 31. Metreletus omelkoi sp. nov., egg: 29. General view. 30 – 31. Micropile. The arrow shows the position and shape of micropile.