Labiobaetis tenasserimensis, 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 tenasserimensis sp. nov.

Figs 7 , 8 , 9

Type material.

Holotype. Thailand • larva; Ratchaburi Prov., Suan Phueng Distr., Bo Klueng ; 13°31'27"N, 99°14'39"E; 180 m; 25.xi.2018; leg. C. Suttinun; on slide; GBIFCH 00763877 ; VMCMU . Paratypes. 7 larvae; same data as holotype; 3 on slides; GBIFCH 00829286 ; GBIFCH 00829275 ; MZL; GBIFCH 00607180 ; VMCMU; 4 in alcohol; GBIFCH 00763853 ; MZL • 3 larvae; Ranong Prov., Mueang Distr., Rak Loi Waterfall ; 09°41'27"N, 98°35'19"E; 78 m; 21.vi.2018; leg. C. Suttinun; 1 on slide; GBIFCH 00829285 ; 2 in alcohol; GBIFCH 00763855 ; VMCMU .

Diagnosis.

Larva. Following combination of characters differentiate L. tenasserimensis sp. nov. from other species of the group numeratus : abdomen dorsally rather uniform brown; hypopharynx with well-developed medial tuft; labial palp segment II lobed, segment III rather short; spines at posterior margin of abdominal tergites wide, apically rounded, mostly not fused.

Description.

Larva (Figs 7 – 9 ). Body length ~ 3.5 mm. Cerci ~ 1 / 2 × body length; paracercus ~ 0.4 × body length. Antenna: ~ 2 × as long as head length.

Colouration (Fig. 7 a – c ). Head and thorax dorsally beige, abdomen dorsally rather uniform brown. Fore protoptera beige with paler striation. Head and thorax ventrally beige, abdomen ventrally brown. Legs off-white to pale grey-brown, femur medially slightly darker. Caudalii pale grey-brown with dark brown band in distal 1 / 2.

Antenna (Fig. 9 k ) with scape and pedicel sub cylindrical, distolateral process at scape absent.

Labrum (Fig. 8 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 four or five 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. 8 i ). Incisor and kinetodontium fused. Incisor with four denticles; kinetodontium with three 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. 8 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 convex, smooth. Tuft of setae on proximal corner of mola present.

Both mandibles with lateral margins almost straight.

Hypopharynx and superlinguae (Fig. 8 e ). Lingua longer than superlinguae. Lingua longer than broad; medial tuft of stout setae well developed. Superlinguae with lateral margins rounded; fine, long, simple setae along distal margin; strongly sclerotised along laterobasal margin.

Maxilla (Fig. 8 f, g ). Galea-lacinia ventrally with two simple, apical setae below canines. Medially with one feathered, spine-like seta and two or three medium to long simple setae. Maxillary palp longer than length of galea-lacinia; 2 - segmented; palp segment II approx. as long as 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. 8 c, d ). Glossa basally broad, narrowing toward apex; shorter than paraglossa; inner margin with ~ 8 robust, spine-like seta, distalmost seta much longer; apex with two long and one medium, robust, apically pectinate setae, and one short seta; 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 two short, simple setae in anteromedial area; dorsally with five 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 0.8 × width of base of segment III; dorsally with row of 4–6 spine-like setae near outer margin. Segment III slightly pentagonal; length ~ 0.8 × maximal width; ventrally covered with short, spine-like, simple setae and short, fine, simple setae.

Hind protoptera vestigial.

Legs (Fig. 9 a – f ). Ratio of foreleg segments 1.4: 1.0: 0.8: 0.3, middle leg 1.3: 1.0: 0.7: 0.3, hind leg 1.4: 1.0: 0.6: 0.3. Femur. Femur length ~ 3 × maximum width. Outer margin with row of five or six spine-like setae and submarginally partial 2 nd row; length of setae ~ 0.2 × 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 or rudimentary on all legs. Tibia. Outer margin with row of short, stout, apically rounded setae, 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 almost bare. Inner margin with row of curved, spine-like setae increasing in length distally. Claw with one row of ~ 14 denticles; distally pointed.

Abdominal terga (Fig. 9 g ). 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, mostly not fused with each other; VI – IX more subtriangular, apically rounded.

Abdominal sterna (Fig. 7 c ). Posterior margin of sterna: I – V smooth, without spines; VI – IX with triangular, apically rounded spines, similar to spines on tergites.

Tergalii (Fig. 9 i, 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 1 / 2 VI combined; tergalius VII as long as segments VIII and 1 / 2 IX combined.

Paraproct (Fig. 9 h ). Distally not expanded, with ~ 11 stout, marginal spines. Surface scattered with U-shaped scale bases and fine, simple setae. Cercotractor with numerous small, marginal spines.

Imago.

Unknown.

Comparison.

The most similar species is L. paranumeratus Kaltenbach & Gattolliat, 2019 from Sumatra. The following characters distinguish the larvae of both species (see Kaltenbach and Gattolliat 2019 b: 62, figs 31, 32): dorsal colour pattern of larval abdomen rather uniform brown in L. tenasserimensis sp. nov. (brown with segment V dark reddish-brown and segment II with dark reddish-brown streaks in L. paranumeratus ); spines on posterior margins of abdominal tergites wide, rounded, mostly with small gaps between them in L. tenasserimensis sp. nov. (wide, rounded and mostly fused in L. paranumeratus ); hypopharynx with medial tuft well developed in L. tenasserimensis sp. nov. (poorly developed in L. paranumeratus ); setae at outer margin of tibia apically rounded, smooth in L. tenasserimensis sp. nov. (apically rounded and with minute serration in L. paranumeratus ).

Etymology.

The species name is derived from the name of the Tenasserim mountain range where it was collected.

Distribution.

Thailand (Fig. 32 b ).

Figures

Figure 7. Labiobaetis tenasserimensis 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 8. Labiobaetis tenasserimensis 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. Scale bars: 20 µm (c, e, f, h, i); 10 µm (a, b, d, g).

Figure 9. Labiobaetis tenasserimensis sp. nov., larva morphology: a. Middle leg; b. Outer margin of middle femur; c. Inner margin of middle femur; d. Outer margin of middle tibia; e. Inner margin of middle tibia; f. Middle claw; g. Posterior margins of abdominal terga; h. Paraproct; i, j. Tergalius IV; k. Antennal base. Scale bars: 50 µm (a); 20 µm (i); 10 µm (b – h, j, k).

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