Labiobaetis jacobusi Kubendran & Balasubramanian, n. sp.

Labiobaetis jacobusi Kubendran & Balasubramanian n. sp.

Figs. 40–58

Material examined. Holotype: male larva: INDIA, Tamil Nadu, Theni, Valipparai stream, Vaigai River, 9o43’35.67” N, 77o31’00.24” E, 1300 m, 29.vii.2012 (ZSI), Colls. Balasubramanian, Kubendran and Selvakumar. Paratypes: 4 male larvae, 6 female larvae and 6 male imagos, same data as holotype (ZSI, MZTC)

Additional material examined. 1 male larva (on slide) and one female larva, INDIA, Tamil Nadu, Kodaikanal, Bas. Manjalaru, Riv. Mulaiyaru, 10o14’19.99”N, 77o29’19.90”E, 1216 m, 29.vii.2012, Colls. Balasubramanian., Kubendran and Selvakumar. 16 larvae, INDIA, Tamil Nadu, Chinnasuruli, Bas. Vaigai, Riv. Suruli falls, 9o42’35.17”N, 77o25’28.62”E, 605 m, 15.ix.2012, Colls. Balasubramanian, Kubendran and Selvakumar. 20 larvae, INDIA, Tamil Nadu, Megamalai, Bas. Highwavys, Riv. Megamalai, 9o43’38.52”N, 77o21’39.34”E, 1485 m, 20.xii.2012, Colls. Balasubramanian, Kubendran and Selvakumar.

Mature larva. Maximal length: Body 5.0–6.0 mm; cerci 2.5–3.0 mm; terminal filament 2.0– 2.5 mm. Size variable between different populations. Colouration: Head uniformly brown without distinct pattern; thorax light brown, legs yellowish brown; abdominal tergites uniformly light brown (Fig. 40); sternites pale yellow (Fig. 41).

Head: Antennae (Fig. 42): Scape and pedicel bare; distolateral notch on scape absent. Labrum (Fig. 43): rectangular, approximately 0.8 times as long as wide, anterior margin with a small median notch; dorsal surface with about 12 spatulate submarginal setae in contiguous row, fine and simple setae scattered medially; ventrally bordered with feathered setae along margin and a distomedial arc of fine setae. Hypopharynx (Fig. 44): lingua covered with short thin setae; stout and longer medially; superlingua with thin setae apically and laterally. Left mandible (Fig. 45): with incisors composed of 7 denticles; prostheca with 5 broad denticles and comb-shaped structure; tuft of setae at apex of mola absent. Right mandible (Fig. 46): with incisors composed of 7 denticles; prostheca with 10 denticles; margin between prostheca and mola and without tubercle; tuft of setae at apex of mola present. Maxillae (Fig. 47) with 4 caninae; lacinia with 2 rows of setae, one row with abundant small setae ending with stout and long setae, second row with 2 long stout dentisetae; two thin setae at base of caninae; palp twosegmented, longer than galea-lacinia; segment 2 longer than segment 1, apically rounded with broadly concave subapical margin, lateral margin with about 9–10 thin setae. Labium (Fig. 48): glossae with one row of simple setae on inner margin; glossae shorter than paraglossae, paraglossae with 2 rows of apical feathered setae; labial palp three-segmented; segment 1 slender, subequal in length to segment 2 and 3 combined; segment 2 with a broad falcated and apically pointed distomedial projection covered with short thin and simple setae scattered over surface; segment 3 somewhat globular, with stout and pointed setae and thin setae scattered on dorsal surface.

Thorax: Foreleg (Fig. 49): dorsal margin of femora with a row of about 7 long stout pointed setae, without row of setae subparallel to margin; ventral margin with about 11 pointed stout setae; dorsal margin of tibiae with a row of setae; dorsal margin of tarsi bare; ventral margin with about 11 pointed stout setae; tarsal claw with one row of about 11 acute teeth (Fig. 50); mid and hind leg similar to foreleg. Hindwing pads absent.

Abdomen: Single lamellate gills on segments 2–7 (Fig. 51), elongated with serrated margins; trachea well visible; each gill with a dark band surrounding margin. Paraproct (Fig. 52) margin with numerous small to medium pointed spines, with scale bases; posterolateral extension with scale bases, margin with irregular spines. Tergites with numerous scale bases; distal-margin with broad triangular spines (Fig. 53). Caudal filaments light brown; terminal filament shorter than cerci and with lateral hairs.

Male imago: Length: body 9.0 mm; fore wing 7.5 mm. Foreleg: femur 1.2 mm; tibia 1.5 mm; tarsi 0.4 mm. Cerci 15–16 mm. Colouration: Head (Figs 55, 56) dark brown; scape and pedicel medium to dark brown; flagellum medium brown; facetted surface of compound eyes reddish brown; lateral face reddish brown. Thorax: dark brown. Legs: femora light brown, tibiae light yellowish brown, tarsi light brown. Forewings (Fig. 54) hyaline; pterostigma with 4 cross-veins generally reaching subcostal vein; double intercalary veins shorter than distance between corresponding main veins (Fig. 57). Hindwings absent. Abdomen (Fig. 54): Tergites I–VI whitish without marking or pattern; tergites VII-X medium brown without marking or pattern, sternites colouration similar to corresponding tergites. Genitalia (Fig. 58): segment 1 and 2 completely fused; inner margin of segment 1 expanded basally, progressively narrower with 6–8 thin setae; segment 2 with parallel margins; segment 3 globular; well developed sclerotized triangular process between forceps, without setae.

Diagnosis. Labiobaetis jacobusi n. sp. can be differentiated from other species of the genus by the following combination of characters: (i) distolateral notch on antennal scape absent (Fig. 42); (ii) a row of 12 spatulate submarginal setae on labrum (Fig. 43); (iii) right mandible without tubercle at inner margin between incisor and mola (Fig. 46); (iv) broadly concave subapical inner margin present on segment 2 of maxillary palp (Fig. 47); (v) segment 2 of labial palp with broad falcate distomedial projection (Fig. 48); (vi) hindwing pads absent; (vii) serrated edges of abdominal gills with well visible trachea on segment 2–7 (Fig. 51); (viii) dorsal margin of tibiae with stout setae (Fig. 49).

Etymology. The species is named in honour of Dr. Luke M. Jacobus for his outstanding contribution to mayfly systematics.

Discussion. Labiobaetis jacobusi n. sp. and Labiobaetis sumigarensis (Müller-Liebenau 1982) from the Philippines are the only species of Labiobaetis from Oriental realm with six pairs of gills, the labrum with spatulate setae, absence of hindwings and absence of antennal scape (Shi & Tong 2014). The two species also possess a similar distomedial projection in segment 2 of labial palp (although more arched in L. sumigarensis, Fig. 5 B in Müller-Liebenau 1982). They differ by the setation of the dorsal margin of femora (numerous short setae in L. sumigarensis (Fig. 5 G in Müller-Liebenau 1982) and long and stout setae in L. jacobusi), the size (L. jacobusi is more than twice the size of L. sumigarensis) and the number of spatulate setae on the labrum. The genus Labiobaetis has a wide distribution all over the world except in Central and South America. Lugo-Ortiz and McCafferty (1997) have expanded the concept of Labiobaetis to include species with or without a distolateral notch on the antennal scape, with the distomedial modification of segment 2 of maxillary palps ranging from a constriction to a pronounced concavity, with or without villopore, with gills present or absent on abdominal segment 1 and with or without hindwing pads. Genetic analysis including Afrotropical and Asian species proved that the present concept of Labiobaetis is polyphyletic (Monaghan et al. 2005; Gattolliat et al. 2008). This riddle can be only solved by comprehensive combined morphological and molecular phylogenetic and phylogeographic studies including all the different known taxa.

Ecology. The type locality is a perennial stream of Vaigai basin with an average of 4 m wide and 40 cm depth and moderate water current (0.9 m /sec) on the southern Western Ghats. The water temperature ranged between 21– 24˚C (seasonal variations) and the pH between 6.7 and 7.3. Larvae were found among grasses in stream edges of medium water flow.