Baetis (Tenuibaetis) bialatus Kluge & Srinivasan & Sivaruban & Barathy & Isack 2023, sp. n.
Creators: name: Kluge, Nikita
name: Srinivasan, Pandiarajan
name: Sivaruban, T.
name: Barathy, S.
name: Isack, Rajasekaran
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Ephemeroptera
Baetidae
Baetis
Baetis bialatus

description: 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).
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).
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).
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).
description: Published as part of 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.), pp. 201-258 in Zootaxa 5277 (2) on pages 237-246, DOI: 10.11646/zootaxa.5277.2.1, http://zenodo.org/record/7889695