Baetiella subansiri Vasanth, Selvakumar & Subramanian, 2020

Vasanth, M., Selvakumar, C., Subramanian, K. A., Sivaramakrishnan, K. G. & Sinha, Bikramjit, 2020, New record of the genus Baetiella Uéno, 1931 (Ephemeroptera: Baetidae) from India with description of a new species and new records for five species, Zootaxa 4763 (4), pp. 563-578 : 564-568

Baetiella subansiri Vasanth, Selvakumar & Subramanian n. sp.

( Figs 1–18 )

Material examined. Holotype: 1 larva, INDIA, Arunachal Pradesh, Lower Subansiri district, Paniya stream, 27.81791 N, 94.09502 E, 993 m, 14.vi.2017, colls. K. A. Subramanian & M. Vasanth (Reg. No. I /E/245) . Paratypes: 2 larvae (1 larva on slide: mouthparts, legs & gills), Arunachal Pradesh, Lower Subansiri district, Bhasskamp stream, 27.75881 N, 94.00912 E, 324 m, 15.vi.2017, colls. K. A. Subramanian & M. Vasanth (Reg. No. I/E/246).

Mature larva. Body length 3.5–4.0 mm, cerci 4.0– 4.5 mm, median caudal filament with 1 segment ( Figs 1–2 ).

Head. Antennae ( Fig. 6 ) light brown, approximately 2 times the width of head; dorsal surface of scape and pedicel bare. Labrum ( Fig. 7 ) almost rectangular, approximately 2.0 times wider than long; anteromedian notch deep with a small rounded lobe at the base, and each side with one medial long setae and a row of 6–8 robust, simple submarginal setae, fine and simple setae scattered posteriorly; ventrally bordered with feathered setae along the anterior margin. Hypopharynx ( Fig. 8 ) with lingua rounded and superlinguae broadly truncate, covered with abundant fine setae distally. Left mandible ( Fig. 9 ): incisors fused with 7 denticles, prostheca robust with 4 blunt and 3–4 acute denticles apically. Right mandible ( Fig. 10 ): incisors with visible fusion line, outer incisor with 3 denticles and inner incisor with 4 denticles, inner incisor margin smooth without fine setae, prostheca with denticles apically and distinctly more slender than the one on left mandible, edge between prostheca and molar smooth without serration. Maxilla ( Fig. 11 ) with three canines and one tooth-like dentiseta on crown of galealacinia, a row of 4–5 long basal setae and basis of galealacinia without hump seta; maxillary palpus 2-segmented, subequal in length, terminal segment with a small pointed tip and numerous setae at apex. Labium ( Fig. 12 ): glossae shorter than paraglossae, with a row of 10–12 stout setae along the inner margin dorsally and 2 long robust blunt setae at the apex; paraglossae approximately 1.5 times wider than glossae, with 3 rows of setae ventrally and 4–5 stout acute setae along the inner margin dorsally; labial palpus 3-segmented, terminal segment conical with a distinctive tip at apex; the 2nd segment without an inner-apical lobe; dorsal surface with numerous pores on the basal segment.

Thorax. Dorsum with 12 distinct tubercles ( Fig. 1 ). Posterior margin of metanotum with a finger-like protuberance medially ( Fig. 1 ). Hindwing pads reduced, approximately 2.5–3.0 times longer than wide. Legs slightly paler than thorax, femora creamy shaded with light brown medially and a brown longitudinal stripe near dorsal margin, tibiae and tarsi brown. All legs with finger-like coxal projection ( Fig. 2 ). Femora with a row of long, robust and simple 17–18 setae on dorsal margin, approximately 1/3 to 1/2 of femur width; femoral villopore reduced; tibiae with irregular row of dense, fine, simple setae dorsally; tarsi with a row of sparse, fine, simple setae dorsally and ventrally with a row of 7–8 robust, pointed setae increasing in length towards apex ( Figs 13–15 ); tarsal claw with two rows of denticles, outer row with 6–7 acute denticles increasing in length apically, inner row with 6–7 short and blunt denticles medially, subequal in length ( Fig. 16 ). All legs with a single very long finger-like white coxal gill ( Fig. 2 ).

Abdomen. Abdominal terga generally dark brown.Posterior margin of terga I–II each with a single posteromedian protuberance, terga III–IX each with a pair of much longer protuberances ( Figs 1–4 ); surface of terga I–IX scattered with round scale-like setae; posterior margin of segments I–V smooth and of segments VI–IX with blunt denticles. Abdominal sterna generally yellowish-white; posterior margins of sterna I–X smooth without denticles or scale-like setae ( Fig. 2 ). Gills (or gill sockets) on segments I–VI ( Fig. 2 ); gills I–V elongate and without tracheation, numerous pores scattered on the surface, smooth fine simple setae along margin ( Figs 17–18 ); gill VI reduced and transparent. Paraproct with numerous pores and fine short setae on surface and 15–16 scale-like setae along the inner margin ( Fig. 5 ). Median caudal filament reduced to one segment ( Fig. 2 ), cerci slightly longer than the body length ( Fig. 1 ).

Imago. Unknown.

Etymology. This species is named after Subansiri river, a major tributary of Brahmaputra river in Lower Subansiri district, Arunachal Pradesh, India.

Distribution. Arunachal Pradesh ( India) ( Fig. 81 ).

Diagnosis. Baetiella subansiri n. sp. and B. macani ( Müller-Liebenau, 1985) share the following characters (i) thoracic dorsum with distinct tubercles; (ii) hindwing pads vestigial; (iii) all legs with a single finger-like white coxal gill; and (iv) median caudal filament reduced to one segment, cerci slightly longer than the body length. However the new species can be distinguished from B. macani by the following combination of characters; (i) gills (or gill sockets) on segments I–VI ( Fig. 2 ); gills I–V elongate and without tracheation, numerous scattered pores on the surface, smooth fine simple setae along margin ( Figs 17–18 ); gill VI reduced ( Figs 3–4 ); (ii) posterior margin of metanotum and abdominal terga I–II each with a single posteromedian protuberance, terga III–IX each with a pair of protuberances and the length of protuberance much longer ( Figs 1–4 ); and (iii) claw with two rows of denticles, outer row with 6–7 acute denticles increasing in length apically, inner row with 6–7 short and blunt denticles medially, subequal in length ( Fig. 16 ).

Baetiella subansiri n. sp. can be accommodated in the recent global key to the larvae of Baetiella ( Shi & Tong 2015) .

The second part of the 4 th couplet of that key can be modified and a new couplet should be added to include B. subansiri n. sp. as follows.

4. Gills (or gill sockets) present on terga I–VII................................................. B. bispinosa (Gose)

- Gills (or gills sockets) absent on tergum VII................................................................ 5

5. Gills I–V elongate; gill VI reduced ( India)..................... B. subansiri Vasanth, Selvakumar & Subramanian n. sp.

- Gills I–VI oval; (or gill sockets) ( China, Vietnam)..................................... B. macani (Müller-Liebenau)

Remarks. Traver (1939) described Baetiella ladakae based on a single male imago collected from Igoo (Igu), Ladak, in Western Himalaya in 1932, during the Yale North India Expedition. Type locality of B. ladakae is a high altitude (> 4000m ASL) stream in cold desert. Baetiella subansiri sp. n. described herein from larval collection could not be compared with the former species since its larvae are unknown. In view of the fact that the type localities of the two species is geographically widely separated, the latter species is described as new to science taking into consideration the remote possibility of larval-adult association of respective species by rearing in the immediate future because of the remoteness of these type localities.

Figures

FIGURES 81. Distribution map of Baetiella in Arunachal Pradesh, India.

FIGURES 1–6. Larva of Baetiella subansiri sp. n. 1. Habitus in dorsal view; 2. Habitus in ventral view; 3. Abdominal terga; 4. Abdominal terga V–VI, closer view; 5. Paraproct; 6. Antennae.

FIGURES 7–12. Larva of Baetiella subansiri sp. n. 7. Labrum; 8. Hypopharynx; 9. Left mandible; 10. Right mandible; 11. Maxilla; 12. Labium.

FIGURES 13–18. Larva of Baetiella subansiri sp. n. 13. Foreleg; 14. Midleg; 15. Hind leg; 16. Hind tarsal claw; 17.Gill I; 18. Gill IV.