Labiobaetis angularis, Kaltenbach & Gattolliat & Boonsoong & Suttinun, 2025

Kaltenbach, Thomas, Gattolliat, Jean-Luc, Boonsoong, Boonsatien & Suttinun, Chanaporn, 2025, New species of Labiobaetis Novikova & Kluge from Thailand (Ephemeroptera, Baetidae), ZooKeys 1258, pp. 213-276 : 213-276

Labiobaetis angularis sp. nov.

Figs 10 , 11 , 12

Type material.

Holotype. Thailand • larva; Petchburi Prov., Kaeng Krachan Distr., Huai Mae Kamoei ; 12°58'42"N, 99°34'55"E; 119 m; 24.ii.2018; leg. C. Suttinun; on slide; GBIFCH 01223079 ; VMCMU . Paratypes. 13 larvae; same data as holotype; 2 on slides; GBIFCH 00829290 , GBIFCH 00829279 ; MZL; 11 in alcohol; GBIFCH 00763867 ; VMCMU • 4 larvae; Kanchanaburi Prov., Thong Pha Phum Distr., Pra Chum Mai ; 14°34'58"N, 98°34'52"E; 269 m; 25.v.2017; leg. C. Suttinun; 1 on slide; GBIFCH 01223081 ; VMCMU; 3 in alcohol; GBIFCH 00829284 , GBIFCH 00763860 ; VMCMU • 2 larvae; Ratchaburi Prov., Suan Pheung Distr., Kang Som Maew ; 13°24'22"N, 99°16'44"E; 207 m; 24.xi.2018; leg. C. Suttinun; 1 on slide; GBIFCH 00829278 ; MZL; 1 in alcohol; GBIFCH 00829291 ; VMCMU • 1 larva; Prachuab Khiri Khan Prov., Kui Buri Dist., Huai Sam Rong ; 100 m; 12°03'50"N, 99°37'39"E; 19.iv.2019; leg. C. Suttinun; in alcohol; GBIFCH 00829287 ; VMCMU • 6 larvae; Petchburi Prov., Kaeng Krachan Distr., Huai Sat Yai ; 12°38'14"N, 99°30'59"E; 162 m; 25.ii.2018; leg. C. Suttinun; in alcohol; GBIFCH 00829277 , GBIFCH 00763858 ; VMCMU • 7 larvae; Petchburi Prov., Kaeng Krachan Distr., Huai Mae Priang ; 12°46'03"N, 99°34'54"E; 142 m; 24.ii.2018; leg. C. Suttinun; in alcohol; GBIFCH 00829280 , GBIFCH 00829274 ; VMCMU; GBIFCH 00763859 ; MZL • 8 larvae; Ratchaburi Prov., Suan Pheung Distr., Pha Wo Tai ; 13°30'57"N, 99°20'40"E; 118 m; 25.xi.2018; leg. C. Suttinun; in alcohol; GBIFCH 00829283 , GBIFCH 00763854 , GBIFCH 00763861 ; VMCMU • 4 larvae; Ranong Prov., Mueang Distr., Klong Nok Ngang ; 09°42'22"N, 98°34'39"E; 11 m; 21.vi.2018; leg. C. Suttinun; in alcohol; GBIFCH 00829273 , GBIFCH 00763856 ; VMCMU • 7 larvae; Ratchaburi Prov., Suan Pheung Distr., Swiss valley ; 13°30'33"N, 99°17'12"E; 140 m; 26.v.2017; leg. C. Suttinun; in alcohol; GBIFCH 00829282 , GBIFCH 00763857 , GBIFCH 00763865 , GBIFCH 00763866 ; MZL • 1 larva; Ratchaburi Prov., Suan Pheung Distr., Bo Wee resort ; 13°28'41"N, 99°14'55"E; 184 m; 24.xi.2018; leg. C. Suttinun; in alcohol; GBIFCH 00829289 ; VMCMU • 2 larvae; Loei Prov., Wang Saphung Distr., Ban Nam Thob ; 17°16'11"N, 101°35'51"E; 318 m; 17.xii.2018; leg. C. Suttinun; in alcohol; GBIFCH 00829281 , GBIFCH 00763862 ; MZL • 3 larvae; Chanthaburi Prov., Khao Khitchakut Distr., Klong Krasue Yai ; 12°52'36"N, 102°05'48"E; 38 m; 05.vi.2018; leg. C. Suttinun; in alcohol; GBIFCH 00829276 , GBIFCH 00763864 ; VMCMU • 1 larva; Prachuap Khiri Khan Prov., Kui Buri Distr., Huai Sam Rong ; 12°03'82"N, 99°37'64"E; 103 m; 19.iv.2019; leg. C. Suttinun; on slide; GBIFCH 00596153 ; VMCMU • 1 larva; Prachuap Khiri Khan Prov., Kui Buri Distr., Klong Kui ; 12°08'17"N, 99°39'77"E; 104 m; 19.iv.2019; leg. C. Suttinun; on slide; GBIFCH 01223080 ; VMCMU .

Diagnosis.

Larva. Following combination of characters differentiate L. angularis sp. nov. from other species of the group numeratus : abdomen dorsally dark grey-brown, laterally off-white; left mandible with angular hump at margin between prostheca and mola; claw with 14–17 denticles; spines at posterior margin of abdominal tergites wide, apically rounded.

Description.

Larva (Figs 10 – 12 ). Body length ~ 3.3 mm. Cerci ~ 1 / 2 × body length; paracercus ~ 0.4 × body length. Antenna: ~ 2 × as long as head length.

Colouration (Fig. 10 a – c ). Head and thorax dorsally dark grey-brown with grey-brown and grey markings; abdomen dorsally dark grey-brown, segment X paler, segments I – VIII laterally off-white. Fore protoptera dark grey and grey-brown. Head and thorax ventrally mainly grey; abdomen ventrally dark grey-brown, segments I and X paler, segments II – V medially paler, segments I – VIII laterally off-white. Legs off-white, femur distomedially with grey-brown band, tibia with long grey-brown streak. Caudalii pale grey with dark grey-brown band in distal 1 / 2.

Antenna (Fig. 12 c ) with scape and pedicel sub cylindrical, distolateral process at scape absent.

Labrum (Fig. 11 a, b ). Sub-rectangular, length 0.7 × maximum width. Distal margin with medial emargination and small process. Dorsally with medium, fine, simple setae scattered over surface; pair of submedian setae, and submarginal arc of ~ 7 long, simple setae on each side, 1 st and 2 nd setae closely together. Ventrally with marginal row of setae composed of lateral and anterolateral long, feathered setae and medial long, bifid setae.

Right mandible (Fig. 11 i ). Incisor and kinetodontium fused. Incisor with four denticles; kinetodontium with four denticles, inner margin of innermost denticle with row of thin setae. Prostheca robust, apically denticulate. Margin between prostheca and mola with pronounced hump. Tuft of setae on proximal corner of mola present. Fine setae scattered along basal margin of mola.

Left mandible (Fig. 11 h ). Incisor and kinetodontium fused. Incisor with four denticles, kinetodontium with three denticles. Prostheca robust, apicolaterally with small denticles and comb-shaped structure. Margin between prostheca and mola with angular hump. Tuft of setae on proximal corner of mola present.

Both mandibles with lateral margins slightly convex.

Hypopharynx and superlinguae (Fig. 11 e ). Lingua approx. as long as superlinguae. Lingua longer than broad; medial tuft of stout setae well developed, short. Superlinguae with lateral margins rounded; fine, long, simple setae along distal margin; strongly sclerotised along laterobasal margin.

Maxilla (Fig. 11 f, g ). Galea-lacinia ventrally with two simple, apical setae below canines. Medially with one feathered, spine-like seta and three or four medium to long simple setae. Maxillary palp longer than length of galea-lacinia; 2 - segmented; palp segment II ~ 1.2 × length of segment I; setae on maxillary palp fine, simple, scattered over surface of segments I and II; apex of last segment without distolateral excavation, apically slightly pointed.

Labium (Fig. 11 c, d ). Glossa basally broad, narrowing toward apex; shorter than paraglossa; inner margin with 9–11 robust, spine-like seta, distalmost seta much longer; apex with three long, robust, apically pectinate setae; outer margin with ~ 4 spine-like setae; ventral surface with fine, simple, scattered setae. Paraglossa sub-rectangular, slightly curved inward; apex rounded; with three rows of long, robust, distally pectinate setae in apical area and ~ 3 medium, simple setae in anteromedial area; dorsally with six long, spine-like setae near inner margin. Labial palp with segment I ~ 0.9 × length of segments II and III combined. Segment II with lobed, thumb-like, distomedial protuberance; distomedial protuberance 0.9 × width of base of segment III; dorsally with row of ~ 5 spine-like setae near outer margin. Segment III slightly pentagonal, apically truncate; length ~ 1.1 × maximal width; ventrally covered with short, spine-like, simple setae and short, fine, simple setae.

Hind protoptera (Fig. 12 g ) vestigial.

Legs (Fig. 12 a, b ). Ratio of foreleg segments 1.3: 1.0: 0.6: 0.3, middle leg 1.3: 1.0: 0.7: 0.3, hind leg 1.4: 1.0: 0.8: 0.3. Femur. Femur length ~ 2.7 × maximum width. Outer margin with row of 4–6 spine-like setae and submarginally partial 2 nd row; length of setae ~ 0.27 × maximum width of femur. Apex rounded, with pair of spine-like setae and short, stout, apically blunt setae. Stout, lanceolate, pointed setae scattered along inner margin; femoral patch absent on all legs. Tibia. Outer margin with row of short, stout, apically rounded setae, sometimes almost bare, distalmost seta larger. Inner margin with two rows of medium spine-like setae; on apex tuft of fine, simple setae. Patella-tibial suture present on basal 1 / 2. Tarsus. Outer margin with row of short, apically rounded setae, sometimes almost bare. Inner margin with row of curved, spine-like setae increasing in length distally. Claw with one row of 14–17 denticles; distally pointed.

Abdominal terga (Fig. 12 e ). Surface with irregular rows of U-shaped scale bases and fine, simple, scattered setae. Posterior margin of terga: I – IX with wide, apically rounded spines, partly fused with each other.

Abdominal sterna (Fig. 12 d ). Posterior margin of sterna: I – VI smooth, without spines; VII – IX with triangular spines.

Tergalii (Fig. 12 h – j ). Present on segments II – VII. Margin with small denticles intercalating fine, simple setae. Tracheae limited to main trunk. Tergalius IV as long as segments V and VI combined; tergalius VII as long as segments VIII and 1 / 2 IX combined.

Paraproct (Fig. 12 f ). Distally not expanded, with ~ 13 stout, marginal spines. Surface scattered with U-shaped scale bases and fine, simple setae. Cercotractor with numerous small, marginal spines.

Imago.

Unknown.

Etymology.

The Latin word angularis, meaning angular, refers to the unique angular hump at the margin between prostheca and mola of the left mandible.

Distribution.

Thailand (Fig. 32 b ).

Figures

Figure 10. Labiobaetis angularis sp. nov., larva: a. Habitus, dorsal view; b. Habitus, ventral view; c. Abdomen, dorsal and ventral view. Scale bars: 1 mm (a, b); 100 µm (c).

Figure 11. Labiobaetis angularis sp. nov., larva morphology: a. Labrum; b. Section of labrum, dorsal focus; c. Labium; d. Labial palp; e. Hypopharynx and superlinguae; f. Maxilla; g. Maxillary palp; h. Left mandible; i. Right mandible; j. Section of left mandible. Scale bars: 20 µm (c, e, f, h, i); 10 µm (a, b, d, g).

Figure 12. Labiobaetis angularis sp. nov., larva morphology: a. Middle leg; b. Middle tarsus and claw; c. Antennal base; d. Abdominal sterna VII – IX; e. Posterior margins of abdominal terga I, V, VIII; f. Paraproct; g. Left half of metanotum with vestigial hind protopteron; h – j. Tergalius IV. Scale bars: 50 µm (a); 20 µm (g, h); 10 µm (b – f, h – j).

Figure 32. Distribution maps: a. Labiobaetis batakorum species group; b. Labiobaetis numeratus species group; c. Labiobaetis operosus species group; d. Labiobaetis sumigarensis species group.