Nigrobaetis (Margobaetis) minutus ( Müller-Liebenau 1984 )

Kluge, Nikita, Sivaruban, T., Srinivasan, Pandiarajan, Barathy, S. & Isack, Rajasekaran, 2024, Redescriptions of Indian species of Nigrobaetis Kazlauskas (in Novikova & Kluge) 1987 (Ephemeroptera, Baetidae), Zootaxa 5418 (5), pp. 528-550 : 534-542

Nigrobaetis (Margobaetis) minutus ( Müller-Liebenau 1984)

( Figs 1–43 )

Baetis minutus Müller-Liebenau 1984: 255 (larva). Baetis (Nigrobaetis) minutus : Novikova & Kluge 1994: 627. Nigrobaetis (Margobaetis) minutus : Kluge 2022: 163 (subimago, misidentified). Nigrobaetis paramakalyani Kubendran & Balasubramanian in Kubendran, Balasubramanian, Selvakumar, Gattolliat & Sivaramakrishnan 2015: 193 (larva, partim), syn. n.; Sivaruban, Srinivasan, Barathy & Isack 2022: 189 (corrections to larval description). Nigrobaetis sumbensis Kaltenbach & Gattolliat 2023: 196 (larva), syn. n.

Material examined. INDIA: State Tamil Nadu: Tirunelveli district, Gadana river , 28.VI.2012, coll. C. Balasubramanian, T. Kubendran & C. Selvakumar: ♂ larva (holotype), 1♀ larva (paratype); Madurai district, river Vaigai , 10.II.2016, coll. N. Kluge & L. Sheyko: 1 L-S♂ ( ZIN); the same locality, 23.IV.2022, coll. P. Srinivasan & R. Isack: 3 larvae ( AMC). State Kerala, Kottayam District, Erumeli , 22.I.2016, coll. N. Kluge & L. Sheyko: 1 L-S-I♂, L-S♂, 3 S-I♂, 1 S-I♀, 2 I ♂, 19 S♂, 9 L ( ZIN). INDONESIA, Sulawesi, Pinrang , 28–31.VIII.2009, coll. N. Kluge & L. Sheyko: 1 L/S♂, 1 L-S-I♀, 1 L/S♀ ( ZIN) .

Additional description of larva. CUTICULAR COLORATION: With more or less contrasting brown and colorless or light areas ( Figs 1–12 ). Pronotum and mesonotum with colorless median stripe of variable, composite shape and paired colorless blanks ( Figs 6, 8, 12 ; Kaltenbach & Gattolliat 2023: fig. 15a). Leg of each pair mostly colorless, with more or less expressed brown transverse band on femur, brown femur-tibia articulation and brown apex of tibia ( Figs 2–4, 9–10 ; Müller-Liebenau 1984: fig. 2i–j; Kaltenbach & Gattolliat 2023: fig. 19a); sometimes nearly entirely colorless. Abdominal tergum I mostly colorless; terga II– III mostly brown, with contrasting paired and unpaired blanks; tergum IV mostly colorless, with pair of contrasting brown spots near anterior margin; terga V –VII mostly brown, with contrasting paired and unpaired blanks; terga VIII –X mostly colorless, with brown posterior margin of tergum X ( Figs 5, 7, 11 ; Müller-Liebenau 1984: fig. 17; Kaltenbach & Gattolliat 2023: fig. 15a). Caudalii mostly colorless, with brown band near middle and apically ( Fig. 5 ; Müller-Liebenau 1984: fig. 2m).

HYPODERMAL COLORATION: Not expressed.

SHAPE AND SETATION: Labrum parallel-sided in proximal half ( Fig. 13 ; Müller-Liebenau 1984: fig. 2a; Kaltenbach & Gattolliat 2023: figs 16a–b). Other mouthparts as in photos ( Figs 14–18 ; Kaltenbach & Gattolliat 2023: figs 16–18).

Hind protoptera or their vestiges absent ( Müller-Liebenau 1984: fig. 2h).

Each tibia with one stout, pointed seta on outer side near apex (subapical seta); middle and hind tibiae, besides subapical seta, with several (2–10) smaller, pointed setae forming irregular longitudinal row on outer side; outer side of fore tibia with no more than one stout seta other than subapical one ( Figs 19–22 ; Müller-Liebenau 1984: figs 2i–j).

Posterior margins of abdominal terga II–X with triangular denticles, shorter and blunter on anterior segments, longer and pointer on posterior segments ( Kaltenbach & Gattolliat 2023: fig. 2a). Posterior margins of abdominal sterna I– VI smooth; posterior margins of sterna VII–IX with sharply pointed, triangular denticles ( Figs 23–24 ). Paraproct with many small denticles ( Fig. 24 ; Müller-Liebenau 1984: fig. 2i; Sivaruban et al. 2022: fig. 4d; Kaltenbach & Gattolliat 2023: fig. 20b). All 7 pairs of tergalii present, relatively long and narrow ( Figs 5, 7, 11 ; Sivaruban et al. 2022: figs 4B, E; Kaltenbach & Gattolliat 2023: figs 15a, 19d–e). In middle part of cercus, each 4th segment with several enlarged denticles on outer side ( Fig. 25 ); paracercus without enlarged denticles.

Descriptions of winged stages

Subimago. CUTICULAR COLORATION: Head colorless, antennal flagellum light brown. Pronotum colorless. Mesonotum light brownish, with brown sutures ( Fig. 28 ). Thoracic pleura and sterna mostly colorless, with certain sclerites brown ( Fig. 27 ). Legs colorless. Abdomen colorless, caudalii and gonostyli colorless.

HYPODERMAL COLORATION: As in imago.

TEXTURE: On middle and hind legs of both sexes, proximal tarsal segment (corresponding to initial 1st+2nd tarsomeres) in proximal part covered with blunt microlepides, in distal part covered with pointed microlepides; other three segments entirely covered with pointed microlepides ( Fig. 34 ). On fore leg of female, 1st tarsomere covered with pointed microlepides; 2nd tarsomere in proximal part covered with blunt microlepides, in distal part covered with pointed microlepides; 3rd–5th tarsomeres entirely covered with pointed microlepides (similar to Fig. 34 ). On fore leg of male, 1st–4th tarsal segments covered mostly with blunt microlepides, apically with pointed microlepides; 5th tarsomere entirely covered with pointed microlepides ( Fig. 33 ).

Imago, male ( Fig. 26 ). Head brown. Turbinate eyes dark reddish-brown. Thorax brown with ochre, equally dark dorsally, laterally and ventrally. Wings colorless, veins ochre-brownish, C and Sc+ R proximad of costal brace brown. Pterostigma with simple, oblique crossveins. Hind wings absent. Legs of all pairs light ochre, either unicolor ( Fig. 26 ), or with apex of femur brown ( Figs 29–30 ). On middle and hind legs, tarsus with 2 apical spines, on 1st+2nd and 3rd tarsomeres. Abdominal terga and sterna I– VI colorless, translucent, with brown spots on spiracles; terga VII–X brown. Cerci ochre.

Male genitalia ( Figs 33–38 ): Styliger with well-outlined, brown median sclerite, to which distal end of sternostyligeral muscle is attached ( Figs 35, 37 ). 1st segment of gonostylus narrowing from base to apex, angulate apically-medially. 3rd (terminal) segment of gonostylus elongate. Penial bridge with prominent, cone-like, sclerotized median projection. Gonovectes sharply bent, with narrow apices.

Imago, female. All abdominal terga brown, sterna ochre with pair of brown stripes laterally ( Figs 31–32 ). On fore leg, tarsus with 2 apical spines, on 2nd and 3rd tarsomeres.

Egg ( Figs 39–43 ). Asymmetric, generally irregularly-oval, with one side more or less stretched. Surface with evenly dispersed small round papillae and irregular folds. Micropile wide.

Dimension. Fore wing length (and approximate body length): male 3.5 mm, female 4 mm.

Distribution. Oriental Region. Described from West Malaysia (as B. minutus ), from Southern India (as N. paramakalyani ) and from Sumba Island in Indonesia (as N. sumbensis ); reported here from Sulawesi island in Indonesia.

Errors in original description of N. paramakalyani . Originally( Kubendran et al.2015), Nigrobaetis paramakalyani was described based on 14 larvae collected in Gadana River in Southern India. Actually, these larvae represented a mixture of two different species, the second one of which was subsequently described as Nigrobaetis klugei Sivaruban et al. 2022 . Holotype of N. paramakalyani is the mature male larva ( Sivaruban et al. 2022: figs 4A–E).

The original description and illustrations of Nigrobaetis paramakalyani contain a mixture of characters belonging to both species. The photos of female larva ( Kubendran et al. 2015: figs 22–23) belong to N. paramakalyani and demonstrate characteristic color pattern of thoracic and abdominal terga. In contrast to this, the drawing of paraproct which bears a few long spines (ibid., fig. 36) belongs to N. klugei , while true paraproct of N. paramakalyani has a higher number of small spines ( Sivaruban et al. 2022: 189 and fig. 4D). The original description of N. paramakalyani states that «Hind wing pads present» and contains the drawing of hind protopteron ( Kubendran et al. 2015: 194 and fig. 33). However, the holotype of N. paramakalyani has no hind protoptera, and the drawing belongs to N. klugei .

Synonymy of N. sumbensis . Nigrobaetis sumbensis Kaltenbach & Gattolliat 2023 was described based on 3 larvae from Sumba Islan in Indonesia. This species was compared with other Nigrobaetis species from Indonesia, Philippines and Malaysia, but not with N. paramakalyani from India. Comparison of N. sumbensis with N. paramakalyani was impossible, because N. paramakalyani was wrongly characterized as having hind wings.

Comparison of N. sumbensis with N. minutus was given in the key ( Kaltenbach & Gattolliat 2023: 228–229), according to which N. sumbensis differs from N. minutus and other species by «Fore femur very slender ..., dorsally slightly concave». Actually, the leg described and figures as «foreleg» is actually middle or hind leg, that is testified by the 4-segmented subimaginal tarsus developing inside ( Kaltenbach & Gattolliat 2023: fig. 19a). As well in many other species, in N. minutus femur of the foreleg is thicker, with straight outer margin ( Figs 2, 9 ), and femora of middle and hind legs are thinner, with concave outer margin ( Figs 3–4, 10 ).

Another characters of N. sumbensis reported in this key, is the number of denticles on claws; variability of their number has not been reported for N. minutus . The third reported character is a tuft of setae-like processes between prostheca and mola of left mandible; the same tuft is figured for N. minutus ( Müller-Liebenau 1984: fig. 2).

Comparison of the larval description of N. sumbensis with our material from India and Sulawesi does not reveal differences. Comparison of egg structure of specimens from India and Sulawesi confirms the wide distribution of this species.

Figures

FIGURES 1–12. Nigrobaetis (Margobaetis) minutus, larvae. 1–6, specimen from Madurai; 7–8, specimen from Erumeli; 9–12, specimen from Pinrang (Sulawesi). 1, exuviae of head; 2–4, exuviae of fore, middle and hind legs; 5, 7, 11, exuviae of abdomen; 6, 8, 12, exuviae of pronotum and mesonotum; 9, 10, fore and hind legs.

FIGURES 13–18. Nigrobaetis (Margobaetis) minutus, larval mouthparts. 13, labrum; 14–15, left and right mandibles; 16, maxilla; 17, paraglossa (focus on dorsal side); 18, labium (focus on ventral side).

FIGURES 19–22. Nigrobaetis (Margobaetis) minutus, exuviae of larval tibia and tarsus. 19–21, fore, middle and hind legs; 22, hind leg of another specimen.

FIGURES 23–25. Nigrobaetis (Margobaetis) minutus, exuviae of larval abdomen. 23, sterna VIII–IX of female; 24, sterna VIII–X of male; 25, fragment of cercus.

FIGURES 26–32. Nigrobaetis (Margobaetis) minutus. 26, male imago; 27, subimaginal exuviae of meso- and metapleura; 28, subimaginal exuviae of mesonotum; 29–30, fore and middle legs of male imago; 31–32, female imago.

FIGURES 33–34. Nigrobaetis (Margobaetis) minutus, male subimago. 33, 3rd–5th tarsomeres of fore leg, 34, apex of tibia and tarsus of hind leg.

FIGURES 35–38. Nigrobaetis (Margobaetis) minutus, genitalia of male imago. 35, ventral view; 36, view with focus on gonovectes and penial bridge; 37, ventral view with focus on sterno-styligeral muscle and median sclerite; 38, lateral view. Abbreviation: m.s, median sterno-styligeral muscle.

FIGURES 39–43. Nigrobaetis (Margobaetis) minutus, eggs.