Baetis (Tenuibaetis) bialatus, Kluge & Srinivasan & Sivaruban & Barathy & Isack, 2023

Kluge, Nikita, Srinivasan, Pandiarajan, Sivaruban, T., Barathy, S. & Isack, Rajasekaran, 2023, Contribution to the knowledge of the subgenus Tenuibaetis Kang & Yang 1994 (Ephemeroptera, Baetidae, Baetis s. l.), Zootaxa 5277 (2), pp. 201-258 : 237-246

publication ID	https://doi.org/ 10.11646/zootaxa.5277.2.1
publication LSID	lsid:zoobank.org:pub:73ED69F3-3887-460D-86DE-C9F1302C8EC3
DOI	https://doi.org/10.5281/zenodo.7889717
persistent identifier	https://treatment.plazi.org/id/03F487D0-A352-4D63-A2DB-FEBAFD7CE925
treatment provided by	Plazi
scientific name	Baetis (Tenuibaetis) bialatus
status	sp. nov.

Treatment

6. Baetis (Tenuibaetis) bialatus sp. n.

( Figs 1–4 View FIGURES 1–4 , 20–21 View FIGURES 13–21 , 184–229 View FIGURES 184–190 View FIGURES 191–194 View FIGURES 195–201 View FIGURES 202–207 View FIGURES 208–210 View FIGURES211–214 View FIGURES 215–224 View FIGURES 225–229 )

Etymology. Allusion of complete absence of hind wings, so that only two fore wings are present.

Material examined ( ZIN). Holotype: L-S-I♁ {specimen [XV](2)2016}, INDIA, Tamil Nadu state, Palni Hills near Kodaikanal, Levinge stream downstream of Pamparpuram , 6.II.2016, coll. N. Kluge & L. Sheyko. Paratypes: the same locality and collectors, 31.I–6.II.2016: 4 L-S-I♁, 2 L-S♁, 5 L-S-I ♀, 51 larvae ); river Palar downstream Perumal Malai , 5.II.2016, coll. N. Kluge & L. Sheyko: 4 larvae .

Descriptions

Larva. CUTICULAR COLORATION: Head brown ( Fig. 186 View FIGURES 184–190 ). Pronotum nearly uniformly brown; mesonotum brown, darker medially and medio-anteriorly ( Fig. 187 View FIGURES 184–190 ). Thoracic pleura brownish, sterna colorless. Legs brown; fore femur with proximal blank oval ( Figs 188–190 View FIGURES 184–190 ). Abdominal terga nearly uniformly brown; tergum IV either as dark as others ( Fig. 184 View FIGURES 184–190 ), or laterally lighter than neighboring ones ( Fig. 185 View FIGURES 184–190 ). Caudalii uniformly brown.

HYPODERMAL COLORATION: Either not expressed, or abdominal terga with dark brown line on posterior margin as in imago (as in Figs 221–222 View FIGURES 215–224 ).

SHAPE AND SETATION: Labrum elongate, narrowing anteriorly ( Fig. 191 View FIGURES 191–194 ). Mandibles — Figs 195–198 View FIGURES 195–201 . Labial glossae, paraglossae and palps relatively long and narrow ( Fig. 194 View FIGURES 191–194 ).

Hind protoptera completely absent ( Fig. 21 View FIGURES 13–21 ).

Stout elongate setae forming row along outer side of femur (including two subapical setae), round in cross section and narrowed toward apex ( Figs 208–210 View FIGURES 208–210 ), distally with single channel, proximally with two channels. Anterior-apical margin of femur with short, blunt two-channel setae ( Fig. 210 View FIGURES 208–210 ).Anterior side of femur with colorless oval scales in semicircular sockets (as on abdomen). Stout two-channel setae on anterior side of femur short ( Fig. 202 View FIGURES 202–207 ).

Stout, two-channel setae on outer side of fore tibia small ( Figs 203, 206 View FIGURES 202–207 , 211–213 View FIGURES211–214 ); stout, two-channel setae on outer sides of middle and hind tibiae significantly larger ( Figs 204–205, 207 View FIGURES 202–207 , 214 View FIGURES211–214 ). Each tibia with similar stout two-channel setae on inner side and along patella-tibial suture.

Denticles on posterior margins of abdominal terga bluntly triangular ( Fig. 199 View FIGURES 195–201 ); absent or sparse on tergum I. Denticles on posterior margins of abdominal sterna absent. Paraproct with small denticles ( Fig. 201 View FIGURES 195–201 ). Tergalii with short scales in semicircular sockets. Tergalius I much smaller than others ( Figs 184–185 View FIGURES 184–190 ). Paracercus significantly smaller than cerci.

Subimago. CUTICULAR COLORATION: Head colorless, antennae brown. Pronotum with light brown and colorless areas. Mesonotum with ochre, light brownish and dark brown areas ( Fig. 216 View FIGURES 215–224 ). Thoracic pleura and sterna with light brownish and dark brown areas ( Fig. 215 View FIGURES 215–224 ). Legs brownish ( Figs 217–218 View FIGURES 215–224 ). All abdominal terga and sterna I–X light brownish with lighter sigilla ( Fig. 223 View FIGURES 215–224 ).

HYPODERMAL COLORATION: Both in male and female, head, thorax, legs and abdomen ochre; abdominal terga I– IX with contrasting reddish-brown band bordering posterior margin and not reaching lateral margins (as in female imago— Fig. 222 View FIGURES 215–224 ).

Imago, male ( Fig. 221 View FIGURES 215–224 ). Head brown. Antennae brown. Turbinate eyes ochre. Thorax brown. Fore wing with membrane colorless or slightly tinged with brownish; veins from ochre (nearer to wing base) to brown; pterostigma with oblique cross veins and disconnected vein fragments. Hind wings entirely absent ( Fig. 20 View FIGURES 13–21 ). Legs uniformly ochre-brownish ( Figs 219–220 View FIGURES 215–224 ). Middle and hind tarsi with 2 apical spines (on 1st+2nd and 3rd segments). Abdominal terga and sterna either uniformly light brown, or terga diffusively darkened with reddish laterally; terga I– IX with darker reddish-brown band bordering posterior margin and not reaching lateral margins. Cerci brown. Gonostyli brown; 3rd (terminal) segment short and petiolate ( Figs 225, 227 View FIGURES 225–229 ). Gonovectes sharply bent, dark brown. Sterno-styligeral muscle vestigial, either without cross-striation ( Fig. 226 View FIGURES 225–229 ), or with cross-striation of few fibrils ( Fig. 228 View FIGURES 225–229 ).

Imago, female ( Fig. 222 View FIGURES 215–224 ). Head, thorax, legs, abdomen and cerci ochre; abdominal terga I– IX with darker reddish-brown band bordering posterior margin and not reaching lateral margins. All tarsi with 2 apical spines (fore tarsus on 2nd and 3rd segments, middle and hind tarsi on 1st+2nd and 3rd segments).

Dimension. Forewing length 6 mm.

Distribution. Mountains of the Western Ghats in southern India (Tamil Nadu).

Comparison. Baetis (Tenuibaetis) bialatus sp. n. differs from most other species of Tenuibaetis by complete absence of hind wings in winged stages and by complete absence of hind protoptera in larvae of all instars ( Figs 20–21 View FIGURES 13–21 ). Larva of B. (T.) bialatus sp. n. differs from another two-winged species, B. (T.) panhai , by longer and narrower labrum, labial glossae, paraglossae and palps ( Figs 191, 194 View FIGURES 191–194 ), by more uniform brown coloration of cuticle on mesonotum and abdominal terga, by pointed and non-flattened setae of outer row on each femur ( Figs 208–210 View FIGURES 208–210 ) and by smaller stout setae on anterior surface of each femur.

From the sympatric species B. (T.) frequentus , larva of B. (T.) bialatus sp. n. differs, besides the absence of hind wings, by two-channel setae on tibiae (rather than pseudo-bifurcate ones) and by pointed and non-flattened stout setae on outers sides of femora; its proximal blank on fore femur is oval ( Fig. 188 View FIGURES 184–190 ), rather than triangular in B. (T.) frequentus ( Fig. 75 View FIGURES 69–77 ). In contrast to B. (T.) frequentus , stout setae on fore tibiae are significantly smaller than such setae on middle and hind tibiae ( Figs 206–207 View FIGURES 202–207 ). Male imago of B. (T.) bialatus sp. n., besides absence of hind wings, differs from B. (T.) frequentus by uniformly brown color of abdomen ( Fig. 221 View FIGURES 215–224 ).

Comment. Larvae from southern India originally described under the name Indobaetis michaelohubbardi Selva-kumar et al., 2012 were said to have ́hindwing pads absent» (Selva-kumar et al. 2012: 127). Later K.G. Sivaramakrishnan (personal communication) reported that actually the type specimens have hind protoptera ( Kluge & Novikova 2014: 215), so this species is not conspecific with B. (T.) bialatus sp. n. Here B. (T.) michaelohubbardi is synonymized with B. (T.) frequentus (see above).