Choroterpes (Dilatognathus) nigella ( Kang & Yang 1994 )

Selvakumar, C., Subramanian, K. A., Chandra, Kailash, Sivaramakrishnan, K. G., Jehamalar, E. Eyarin & Sinha, Bikramjit, 2017, A new species and a new record of the subgenus Dilatognathus Kluge 2012 (Ephemeroptera: Leptophlebiidae: genus Choroterpes Eaton, 1881) from India, Zootaxa 4268 (3), pp. 439-447 : 444-447

Choroterpes (Dilatognathus) nigella ( Kang & Yang 1994)

( Figs. 21–36 )

Material examined. 3 larvae, Arunachal Pradesh, Lower Subansiri District, Ranga River , 27.3964 N, 93.7573 E, 625 m, 21.iv.2015, colls. K. A. Subramanian & Bikramjit Sinha ; 10 larvae, INDIA, West Bengal, Darjeeling (Sikkim border), Rishikhola, Rishi river , 27.1696 N, 88.6351 E, 554 m, 23.iii.2013, coll. Srimoyee Basu ; 5 larvae, Meghalaya, Jaintia Hills district, Wah Malidar, Malidar village , 3.ii.2007, colls. J. Lyngdoh & Party.

Description. Larva. Body length 5 mm, cerci 5 mm, median filament 6 mm ( Fig. 21 ). Labrum wide, median emargination deep, with sharp semicircular impression on dorsal surface; proximal transverse row of setae interrupted medially; instead of distal transverse row, a wide fringe of irregularly situated setae, smaller than setae of the proximal transverse row; most part of dorsal surface with irregularly arranged long and thin setae, somewhat smaller than setae of distal stripe; closely set long setae laterally ( Fig. 22 ). Lingua of hypopharynx with well developed lateral processes, anterior margin shallowly cleft ( Fig. 23 ). Mandibles with outer margin moderately convex and with closely set long setae medially ( Figs. 24–25 ). Maxilla with inner-apical angle produced as tusklike process with 3 simple setae at base; palp elongated and bears long filtering setae; 2nd segment in apical part of inner side with a few setae forming a longitudinal row; 3rd segment with a proximal semicircular transverse row of setae on inner side and fields of irregularly situated setae along with ventral and dorsal sides ( Fig. 26 ). Labium with paraglossae widened, expanded laterally; palp elongated, with long filtering setae form regular longitudinal rows; segment 2 with double row on outer side and a row on dorsal side; segment 3 with a row on outer side and a row on inner side; dorsal side of 3rd segment also bears smaller irregularly situated setae ( Fig. 27 ).

Legs pale yellowish; each femur with dark brown spots at middle and near apex; fore femur also with a brown spot near base, widest proximally; middle and hind femur widest at middle. Femora with irregularly situated stout setae of various lengths, dorsal side of fore femur with few setae, dorsal side of middle and hind femur with many setae. Stout setae on inner side of fore tibiae situated dense and irregularly placed, pointed and bipectinate. Inner side of middle tibia with few stout setae. Inner side of hind tibia with a sparse row of stout setae; outer side of hind tibia with stout setae of variable length, as on outer side of femur. Outer sides of all tibiae with irregularly situated thin hairs, whose length exceed tibia width ( Figs. 28–30 ). Claws apically hooked, a row of subequal sized denticles on claws ( Fig. 31 ). Hind wing pad present.

Abdomen without stout setae; posterolateral margins of abdominal terga with pointed denticles, size of denticles increases from tergum 6 to tergum 9. Posterior margins of abdominal terga 1–2 with row of with small, spine-like denticles; terga 3–7 with row of long, thin, spine-like denticles; terga 8–9 with row of short spine-like denticles at middle, long denticles at corner; sterna without denticles. Each segment of abdominal tergum brown with lighter blanks adjacent to anterior margin. Gill I absent; gills II–VII with dorsal and ventral lamellae terminated in 3 processes, with median process longer than laterals; gills II–V equal size, gill VI smaller, gill VII smallest ( Figs. 32–36 ). Terminal filament longer than cerci with a whorl of setae on alternate segments; setae longer than length of corresponding segment.

Adult. Unknown.

Distribution. India, Thailand, Hainan and Taiwan Islands.

Diagnosis. Choroterpes (D.) nigella ( Kang & Yang 1994) can be distinguished from all other species by the labrum with deep median emargination and sharp semicircular impression on the dorsal surface ( Fig. 22 ).

Remarks. Choroterpes (D.) nigella ( Kang & Yang 1994) was originally described from Taiwan based on larvae and eggs. Kluge (2014) examined the specimens from Thailand and Hainan Island and provided additional characters. The new record of the larvae Choroterpes (D.) nigella ( Kang & Yang 1994) from Arunachal Pradesh, Meghalaya and West Bengal is extension of its distributional range.

Discussion. Flowers (2009) made a detailed analysis of the origin and present distribution of the genus Choroterpes but did not include the Oriental subgenera. Kluge (2012) delineated the salient features of the subgenus Dilatognathus and has dealt with the evolution of Dilatognathus type of nymphal mouthparts in 5 phylogenetically unrelated taxa of Leptophlebiidae viz., Dilatognathus, Notophlebia , Hagenulus , Ulmeritus and Hermanellognatha ( Kluge 2012). Both the species described herein have Dilatognathus type mouthparts, one with a long maxillary tusk and another without a maxillary tusk. Mouthpart architecture of both the species endorses the phylogenetic approach of Kluge (2012) and his view of presence or absence of maxillary tusks and different patterns of filter-feeding accessories within the subgenus Dilatognathus. The occurrence of Dilatognathus- type mouthparts in different genera of the tribes, Choroterpini, Hagenulini and Iscini, is ultimately an instance of convergent evolution to filter feeding in rock bottomed, silt encrusted streams with moderate flow.

Figures

FIGURES 21 – 27. Larva of Choroterpes (D.) nigella (Kang & Yang 1994). 21. Dorsal view of male; 22. Labrum; 23. Hypopharynx; 24. Left mandible; 25. Right mandible; 26. Maxillae; 27. Labium.

FIGURES 28 – 36. Larva of Choroterpes (D.) nigella (Kang & Yang 1994). 28. Foreleg; 29. Midleg; 30. Hindleg; 31, Claw; 32. Gill II; 33. Gill III; 34. Gill IV; 35. Gill V; 36. Gill VII.