Contribution to the knowledge of the subgenus Tenuibaetis Kang & Yang 1994 (Ephemeroptera, Baetidae, Baetis s. l.) Author Kluge, Nikita Department of Entomology, Saint Petersburg State University, Universitetskaya nab., 7 / 9, Saint Petersburg, 199034, Russia. Website: http: // insecta. bio. spbu. ru Author Srinivasan, Pandiarajan PG and Research department of Zoology, the American College, Madurai- 625002, India Author Sivaruban, T. 0000-0001-8997-9355 PG and Research department of Zoology, the American College, Madurai- 625002, India & sivaruban 270 @ gmail. com; https: // orcid. org / 0000 - 0001 - 8997 - 9355 sivaruban270@gmail.com Author Barathy, S. Department of Zoology, Fatima College, Madurai- 625018, India Author Isack, Rajasekaran 0000-0002-9952-4335 PG and Research department of Zoology, the American College, Madurai- 625002, India & iceisack 143 @ gmail. com; https: // orcid. org / 0000 - 0002 - 9952 - 4335 iceisack143@gmail.com text Zootaxa 2023 2023-05-02 5277 2 201 258 http://dx.doi.org/10.11646/zootaxa.5277.2.1 journal article 10.11646/zootaxa.5277.2.1 1175-5326 7889695 73ED69F3-3887-460D-86DE-C9F1302C8EC3 6. Baetis ( Tenuibaetis ) bialatus sp. n. ( Figs 1–4 , 20–21 , 184–229 ) 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 ). Pronotum nearly uniformly brown; mesonotum brown, darker medially and medio-anteriorly ( Fig. 187 ). Thoracic pleura brownish, sterna colorless. Legs brown; fore femur with proximal blank oval ( Figs 188–190 ). Abdominal terga nearly uniformly brown; tergum IV either as dark as others ( Fig. 184 ), or laterally lighter than neighboring ones ( Fig. 185 ). 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 ). SHAPE AND SETATION : Labrum elongate, narrowing anteriorly ( Fig. 191 ). Mandibles — Figs 195–198 . Labial glossae, paraglossae and palps relatively long and narrow ( Fig. 194 ). Hind protoptera completely absent ( Fig. 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 ), distally with single channel, proximally with two channels. Anterior-apical margin of femur with short, blunt two-channel setae ( Fig. 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 ). Stout, two-channel setae on outer side of fore tibia small ( Figs 203, 206 , 211–213 ); stout, two-channel setae on outer sides of middle and hind tibiae significantly larger ( Figs 204–205, 207 , 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 ); absent or sparse on tergum I. Denticles on posterior margins of abdominal sterna absent. Paraproct with small denticles ( Fig. 201 ). Tergalii with short scales in semicircular sockets. Tergalius I much smaller than others ( Figs 184–185 ). 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 ). Thoracic pleura and sterna with light brownish and dark brown areas ( Fig. 215 ). Legs brownish ( Figs 217–218 ). All abdominal terga and sterna I–X light brownish with lighter sigilla ( Fig. 223 ). 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 ). Imago, male ( Fig. 221 ). 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 ). Legs uniformly ochre-brownish ( Figs 219–220 ). 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 ). Gonovectes sharply bent, dark brown. Sterno-styligeral muscle vestigial, either without cross-striation ( Fig. 226 ), or with cross-striation of few fibrils ( Fig. 228 ). FIGURES 184–190. Baetis ( Tenuibaetis ) bialatus sp. n . , larval exuviae (one and the same magnification). 184–185, abdomen; 186, head with labrum; 187, half of pronotum and mesonotum; 188–190, fore, middle and hind legs. Imago, female ( Fig. 222 ). 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 ). FIGURES 191–194. Baetis ( Tenuibaetis ) bialatus sp. n . , larval mouth parts. 191, labrum; 192, hypopharynx with superlinguae; 193, maxilla; 194, labium. FIGURES 195–201. Baetis ( Tenuibaetis ) bialatus sp. n . , larvae. 195–196, left and right mandibles with developing mandibles of next instar inside; 197–198, the same of another individual; 199, exuviae of abdominal tergum IX; 200, abdominal tergum II; 201, paraprocts. Abbreviations: hirud, hirudiform seta; sq, scale. FIGURES 202–207. Baetis ( Tenuibaetis ) bialatus sp. n . , larval legs. 202, middle femur (anterior side); 203, fore tibia (anterior side); 204, middle tibia (anterior side); 205, middle tibia (outer side); 206–207, tibia and tarsus of fore and middle legs (anterior side) (202–204, 206–207, holotype). Abbreviations: 2-can, two-channel seta. FIGURES 208–210. Baetis ( Tenuibaetis ) bialatus sp. n . , proximal, middle and distal portions of larval femur (view from outer side). Abbreviations: 2-can, two-channel seta; ant-ap, anterior-apical margin of femur; hirud, hirudiform seta; post-ap, posteriorapical margin of femur. FIGURES 211–214. Baetis ( Tenuibaetis ) bialatus sp. n . , larval tibiae (view from outer side). 211–213, fore tibia; 214, middle tibia. 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 ). 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 ), 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 ) 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 ), rather than triangular in B . ( T .) frequentus ( Fig. 75 ). 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 ). 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 ). FIGURES 215–224. Baetis ( Tenuibaetis ) bialatus sp. n . 215, subimaginal exuviae of mesopleuron; 216, subimaginal exuviae of half of mesonotum; 217–218, exuviae of fore and hind legs of male subimago; 219–220, fore and middle legs of male imago; 221, male imago; 222, female imago; 223, subimaginal exuviae of abdominal segments VIII–IX; 224, egg (215–220, holotype). FIGURES 225–229. Baetis ( Tenuibaetis ) bialatus sp. n . , genitalia of male imago. 225, 227, ventral view; 226, 229, ventral view with focus on sterno-styligeral muscle; 228, enlarged fragment of sterno-styligeral muscle to show cross-striation (225–226, holotype). Abbreviations: gv, gonovectis; s.s, sterno-styligeral muscle. 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).