Platybaetis arunachalensis Vasanth, Kubendran, Subramanian & Gattolliat, 2025

Platybaetis arunachalensis Vasanth, Kubendran, Subramanian & Gattolliat sp. nov.

( Figs 1–7 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 , 15A View FIGURE 15 , 16 View FIGURE 16 )

Material examined. Holotype: mature larvae, India, Arunachal Pradesh, Upper Siang district, Yingkiong (20 km away from Yingkiong Town towards north), 28.65781°N, 95.0186°E, 333 m; 24.II.2024, coll. T. Kubendran, Reg. no. I/E/ 842 Paratypes: 8 larvae, same data as holotype, Reg. no. I/E/843 GoogleMaps GoogleMaps . Additional material examined: 10 larvae (2 mature larvae on slide), India, Arunachal Pradesh, Upper Siang district, Yingkiong, Komku Village near Bridge , 28.52581°N, 95.0483°E, 439 m, 26.II.2024, coll. T. Kubendran GoogleMaps .

Description. Larva ( Figs 1A–C View FIGURE 1 , 2A View FIGURE 2 ): male: body length 6.5–7.0 mm, cerci 4.0– 4.5 mm, antennae 1.2–1.3 mm ( Fig. 4E View FIGURE 4 ); female: body length 8.5–9.0 mm, cerci 5.5–6.0 mm, antennae 1.3–1.4 mm; median caudal filament three segments ( Figs 7B, C View FIGURE 7 ).

Head: Flattened, slightly wider than long; brownish yellow with diffusive black irregular markings, sometimes poorly visible; frons and vertex with brown markings; male turbinate eye reddish ( Figs 1A–C View FIGURE 1 , 2A View FIGURE 2 ). Antennae brown with pale, scape thick and small setae on anterior margin with base broader, pedicel cylindrical, and flagellum brown with pale, slightly shorter than head width, small hair-like setae on each segment ( Figs 3A View FIGURE 3 , 4E View FIGURE 4 ). Posterior margin of head without incision ( Figs 1A View FIGURE 1 , 2A View FIGURE 2 ). Labrum ( Figs 3B, C View FIGURE 3 ) anterior margin rounded, 2.0× wider than long; distal margin with row of apically hair-like setae and feathered setae, dorsal surface with hair-like and numerous stout setae; arc of 1+3 stout medium setae. Distal margin with medial emargination without any crenation ( Fig. 3C View FIGURE 3 ). Mandibles: incisors fused with blunt denticles ( Figs 3E–G View FIGURE 3 ); right mandible ( Fig. 3E View FIGURE 3 ) incisors with 6–7 denticles, prostheca stick-like poorly developed, tuft of setae at apex of mola reduced, dorsal margin smooth. Left mandible ( Figs 3F, G View FIGURE 3 ) incisors with 7–8 denticles; prostheca comb-shaped; mola with thumb-like long apical extension. Basal half with few short simple setae scattered over dorsal surface. Hypopharynx ( Fig. 3D View FIGURE 3 ) with small, thin setae and well-developed lingua and superlingua. Maxillae ( Fig. 4D View FIGURE 4 ) with three dentisetae and 3 canines; setae of inner dorsal row 1.2× longer than setae of inner ventral row; palps 2-segmented; segment II longer than segment I with inner margin deeply curved and outer margin slightly curved; segment II with small rounded projection at apex surrounding by a few simple setae. Labium ( Figs 4A–C View FIGURE 4 ) with glossae slightly longer than paraglossae; glossae with blunt stout setae at apex ( Figs 4B–C View FIGURE 4 ); a few small stout setae on dorsal margin; 7–8 long, stout setae on inner margin and a long, stout seta in middle; paraglossae broad with 3 rows of long, stout setae apically; dorsal surface with long, stout setae; palps 3-segmented, segment I narrow with several micropores on dorsal surface ( Fig. 4A View FIGURE 4 ); segment II small, outer margin with short, fine, simple setae; dorsally with several micropores; ventrally with three medium, simple setae. Segment III slightly rounded with several short, stout acute setae ( Fig. 4A View FIGURE 4 ).

Thorax: Yellowish brown ( Figs 1A–C View FIGURE 1 , 2A–C View FIGURE 2 ). Pronotum nearly as broad as head capsule ( Figs 1A–C View FIGURE 1 , 2A View FIGURE 2 ); pronotum posterolateral margin rounded. Ventral side of pronotum and mesonotum with medial suture ( Fig. 2B View FIGURE 2 ). Hindwing pads absent. Legs generally brownish yellow with a pale-yellow pattern ( Figs 5A–C View FIGURE 5 , 6A–C View FIGURE 6 ). Foreleg ( Figs 5A View FIGURE 5 , 6A View FIGURE 6 ): femur apex slightly rounded, dorsal surface with small, stout for scattered setae, outer margin with a row of long feathered and ciliate setae ( Fig. 6D View FIGURE 6 ), inner margin with small, stout for scattered setae roughly arranged in two rows ( Fig. 4A View FIGURE 4 ); femur and tibia of similar length, dorsal margin with row of long, hair like setae and few short stout setae ( Fig. 5A View FIGURE 5 ), patella tibial suture present along with long hair-like setae ( Fig. 6E View FIGURE 6 ); tarsus 2.3× shorter than tibia, with dorsal row of simple setae, inner margin with a row of short, stout setae ending with fine, long seta near apex ( Fig. 6A View FIGURE 6 ), claw with single row of six denticles increasing in size towards apex, with few apical stripes, subapical setae absent ( Fig. 6F View FIGURE 6 ). Middle and hind legs same as forelegs ( Figs 5B View FIGURE 5 , 6B View FIGURE 6 ; 5C View FIGURE 5 , 6C View FIGURE 6 ).

Abdomen: Coloration of terga generally brown with yellowish brown pattern ( Figs 1A–C View FIGURE 1 , 2A View FIGURE 2 ); terga I–IV brown with yellow pattern, medially with cross line marking and along with a pair of black spots; tergum V pale yellow with brown marks laterally; VI–VII brown, VIII pale yellow with medially a pair of black spots, IX–X brown. Posterior margin of abdominal terga I–X with blunt denticles ( Fig. 7A View FIGURE 7 ). Sterna I–X ecru mixed with yellow. Gills present on segments I–VII, simple, leaf-like, and rather broad; tracheae black on gills I–VII, margin without minute setae ( Figs 7D–J View FIGURE 7 ). Paraproct distally slightly expanded and without marginal spines, surface covered with small rounded scale bases, fine simple setae, and small micropores ( Fig. 7K View FIGURE 7 ). Posterolateral extension (cercotractor) with small spines. Cerci shorter than body length; paracercus composed of only 3 segments ( Figs 7B–C View FIGURE 7 ).

Imago: Unknown.

Distribution: Arunachal Pradesh ( India) ( Figs 15A View FIGURE 15 ).

Etymology: The species is named after the state of Arunachal Pradesh.

Diagnosis: Platybaetis arunachalensis sp. nov. is rather similar to P. nayokensis ; it can be distinguished by the following combination of characters: (i) labrum with arc of 3 medium setae and medial emargination without any crenation ( Figs 3B–C View FIGURE 3 ); (ii) incisors of mandibles fused with blunt denticles ( Figs 3E–G View FIGURE 3 ); (iii) glossae with blunt stout setae at apex ( Figs 4B–C View FIGURE 4 ); (iv) labial palp segment I narrow with several micropores on dorsal surface ( Fig. 4A View FIGURE 4 ); (v) hindwing pads absent; (vi) claw with 6 denticles, apical denticle larger than others ( Fig. 6F View FIGURE 6 ); (vii) posterior margin of abdominal terga I–X with blunt denticles ( Fig. 7A View FIGURE 7 ); (viii) paracercus composed of 3 segments ( Figs 7B–C View FIGURE 7 ).

Ecology: Larvae of P. arunachalensis sp. nov. was collected from tributaries of the Brahmaputra River near Yingkiong in the Upper Siang district of Arunachal Pradesh ( Fig. 15A View FIGURE 15 ). These waterbodies are situated approximately 20 km north of Yingkiong town. The water flow near the bridge was notably strong. This new species was found in association with other Baetidae (including Labiobaetis spp. and Acentrella (Liebebiella) vera ), Vietnamellidae , and Heptageniidae . Environmental parameters recorded at the site include: air temperature: 27.1°C, water temperature: 22.2°C, humidity: 83%, pH: 6.34, and an open canopy. The river substrate was composed of 10% gravel, 10% cobbles, 20% boulders, 50% bedrock, 5% fine sand, and 5% silt. Consistent with the observations of Kluge and Novikova (2011) and Suttinun et al. (2018), larvae show a preference for wet rocks moistened by fine water spray, particularly on large stones near small waterfalls or in the interstices between large rocks in fast flowing water.