Sparsorythus srokai Srinivasan et al.

(Figs. 1–7)

Sparsorythus srokai Srinivasan, Sivaruban, Barathy & Isack, 2022: 186 (larva).

Material examined: 5 male (ZSI-SRC, Reg. No.: I/E-733), 5 female imagoes (ZSI-SRC, Reg. No.: I/E- 734) and 5 male, 5 female subimagoes with final instar larval exuvia, INDIA, Tamil Nadu, Dindigul district, Pullaveli falls, 10.303570° N, 77.752182 °E; 1650 m. a.s.l., 09.III.2022, Colls. Balasubramanian & Muthukatturaja .

Descriptions

Male imago (Fig. 1): body length, 3.2–3.4 mm; cerci length, 16.2–17.5 mm; terminal filament, 18.0– 19.5 mm; length of head, 0.2 mm; width of head, 0.8 mm; length of antenna, 0.5 mm; length of forewing, 4.8–5.0 mm; width of forewing 2.3–2.5 mm; dorsal diameter of eye 0.2 mm; distance between compound eyes 0.4 mm; length of fore femur: tibia: tarsus (mm): 0.6: 0.7: 0.5. General body coloration greyish brown to pale yellow. Head: grey to pale brown, anterior margin and area around antennal base pale grey; scape and pedicel grey, flagellum translucent; compound eyes black. Thorax: pronotum grey to pale yellow, meso and metanotum yellowish brown to pale yellow, margins darker. Legs: femur grey, tibia and tarsi translucent; fore tibia slightly longer than femur; middle and hind tibia equal in length to corresponding femur; foreleg with two paddle-like claws, middle and hind legs with one claw paddle-like and the other apically hooked. Wings: hyaline with grey shading in basal area of C and Sc (Fig. 3); pterostigmatic region faint grey, usually no discernible cross veins in costal space; venation mostly grey; C and Sc grey; two cross veins between MA 2 and MP 1; cross veins of CuP and AA frequently not visible along their entire length.Abdomen: terga pale grey to yellowish brown; sterna paler; terga with grey smudges on lateral margin; dorsomedial line paler. Genitalia (Fig. 5): styliger plate slightly protruded; forceps two segmented; distal segment slightly longer than basal segment, length (mm) = 0.15: 0.20; forceps base broad, without tiny bristles; inner margin of segment two of forceps covered with numerous short, leaf-shaped attachment structures; penis lobes simple, straight and tubular, swelled near base, slightly bent in dorsal direction (live specimen); penis apex reaching approximately 2/3 of second segment of forceps; apex of penis rounded, with distinct medial emargination (Fig. 6). Caudal filaments: translucent, basal 1/2 of each segment with grey smudge; approximately five times longer than body length, cerci glabrous, terminal filament slightly longer than cerci.

Male subimago: similar to imago, general body coloration yellowish grey to pale yellow; head grey to pale yellow, scape and pedicel grey, flagellum translucent; compound eyes black; pronotum grey to pale yellow, meso- and metanotum yellowish brown to paler, margins darker; femur grey, tibia and tarsi translucent; femur subequal in length to tibia; foreleg with two paddle-like claws, middle and hind legs with one claw paddle-like and the other apically hooked; forewings with grey shading and sparse microtrichia on margins; pterostigmatic region paler; venation mostly grey; tergum pale gray, sternum paler; tergum with grey smudges on lateral margin; genitalia almost as in imago; cerci and terminal filament longer than body, but distinctly shorter than in imago.

Female imago (Fig. 2): body length, 3.8–4.0mm; cerci length, 5.5–6.0 mm; terminal filament, 7.5–8.0 mm; length of head, 0.4 mm; width of head, 1.2 mm; length of antenna, 0.6 mm; length of forewing, 6.0– 6.3 mm; width of forewing, 2.3–2.6 mm; dorsal diameter of eye 0.25 mm; distance between compound eyes 0.7 mm; length of fore femur: tibia: tarsus (mm): 0.7: 0.75: 0.4. General coloration similar to male. Head: dark grey to pale grey, anterior margin and area around antennal base grey to pale grey; scape and pedicel grey, flagellum pale grey to translucent; compound eyes black. Thorax: pronotum grey to pale yellow, meso and metanotum brownish yellow to pale yellow, margins darker. Legs: foreleg femur and tibia grey, and tarsi pale grey to translucent; coloration of middle and hind legs similar to male. Wings (Fig. 4): coloration similar to male imago; four cross veins between MA 2 and MP 1; cross veins between CuP and AA frequently not visible along their entire length (some specimens with these cross veins and other without). Abdomen: terga grey; sterna pale yellow; terga with grey smudges on lateral margin; dorsomedial line paler. Caudal filaments: translucent, basal 1/2 of each segment with grey smudge; approximately two times longer than body length, cerci glabrous, terminal filament slightly longer than cerci.

Female subimago: body length, 3.0– 3.5 mm; length of fore wing, 5.4–5.8 mm; width of forwing, 2.2–2.4 mm; cerci and terminal filament length 2.5–3.0 mm. General body coloration dark grey to pale yellowish grey; head coloration darker; composed eyes, black, distanced approximately half of mesonotum width; basal half of ocelli darker and apical portion paler or white; antennal pedicle approximately 2 times longer than scape; pronotum coloration darker with a small blank area on either side of the ecdysial suture at posterior margin; dorsum of meso and metanotal regions with pale yellowish grey makings; femora of legs pale grey, basal end of fore femur, tibia and tarsus transparent; tarsal claws double on all legs, posterior margin of both claws paddle-like on forlegs, and one paddle-like and the other apically hooked on middle and hind legs; forewing coloration pale grey, with numerous microtrichia on dorsal surface and margins; abdominal terga I–VII dark, remainders with pale yellowish grey markings; median od thoracic sternum with a grey longitudinal markings; abdominal sterna paler; posterior margin of subanal (sternum IX) plate triangular in shape, posterior margin smoothly rounded; cercus and terminal filament little smaller than the body length, coloration as in male imago.

Diagnosis. Imago: (i) forewings of male shaded with grey color in basal area of C and Sc regions; (ii) penis apex reaching approximately 2/3 of second segment of forceps; posterior margin of subanal plate (sternum IX) in female imago triangular, smoothly rounded at apex.

Ecology of Sparsorythus srokai . Pullaveli stream is a tributary of Kamarajar Sagar dam (also known as Athoor Dam) and runs through conserved forest and cultivated areas of the Western Ghats, Dindigul district, Tamil Nadu (Fig. 7). In the collection site, the maximum width of the river is around ~ 15 meters, and wet width 5 meters; water depth ~ 30–45 cm. The current velocity of the water was 1.0 m/sec at the time of collection, sandy substratum mainly with boulders, cobbles, pebbles, sand and silt, canopy cover about 80%. Water pH is about 7.2–7.4; water temperature is 24±2°C and air temperature about 27°C ±2°C. The larvae are mainly associated with the submerged roots of the riverside vegetation. Larvae of Sparsorythus srokai were associated with other mayfly genera such as Thalerosphyrus Eaton, 1881 (Heptageniidae), Teloganodes Eaton, 1882 (Teloganodidae), Choroterpes Eaton, 1881 (Leptophlebiidae), Ephemera Linnaeus, 1758 (Ephemeridae), Procloeon Bengtsson 1915, Baetis Leach, 1815 and Nigrobaetis Novikova & Kluge, 1987 (Baetidae) . Adults of the species generally emerged in the dusk (about 6.00 pm to 8.00 pm).