Two new species and a new record of the ant genus Meranoplus Smith, 1853 (Hymenoptera, Formicidae, Myrmicinae) from Thailand Author Yodprasit, Kuntima https://orcid.org/0009-0000-5012-0498 Department of Forest Biology, Faculty of Forestry, Kasetsart University, Bangkok, 10900, Thailand Author Buddhakala, Nopparat 0000-0002-8353-3851 Division of Biology, Faculty of Science and Technology, Rajamangala University of Technology Thanyaburi, Pathum Thani, 12120 Thailand Author Tasen, Wattanachai https://orcid.org/0009-0004-1794-6940 Department of Forest Biology, Faculty of Forestry, Kasetsart University, Bangkok, 10900, Thailand Author Jaitrong, Weeyawat 0000-0003-1362-0754 Division of Biology, Faculty of Science and Technology, Rajamangala University of Technology Thanyaburi, Pathum Thani, 12120 Thailand & Office of Natural Science Research, National Science Museum, 39 Moo 3, Khlong 5, Khlong Luang, Pathum Thani, 12120, Thailand text ZooKeys 2024 2024-08-26 1210 207 227 journal article 10.3897/zookeys.1210.125990 B158276E-7AC6-40AF-8713-0881D42F3953 Meranoplus siamensis Yodprasit & Jaitrong sp. nov. Figs 2 A – D , 5 H – I , 6 A Types. Holotype : • worker ( THNHM -I-00027303 , THNHM ), eastern Thailand , Chonburi Province , Sri Racha District , Kasetsart Sriracha Campus , dry evergreen forest , 13.2837 ° N , 100.9238 ° E , 18 October 2003 , W. Jaitrong leg., TH 03 - WJT- 313. Paratypes : • 6 workers ( THNHM -I-00027304 to THNHM -I-0002730 , THNHM -I-00027310 , THNHM -I-00028942 ), same data as holotype • 4 workers ( THNHM -I-00027309 , THNHM -I-00027311 to THNHM -I-00027313 ) • 3 workers ( THNHM -I-00027314 ), same locality as holotype, but 19. IV. 2003 , A. Suwanasri leg., AS 190403-01 . The paratypes are deposited in THNHM . Non-type material examined. Central : • 1 worker ( THNHM -I-00028919 , THNHM ), central Thailand , Uthai Thani Province , Ban Rai District , Kaen Ma Kurd Village , dry dipterocarp forest , 15.1225 ° N , 99.2755 ° E , 1 June 2002 , W. Jaitrong leg., TH 02 - WJT- 039 ; 21 workers ( THNHM -I-00028920 to THNHM -I-00028940 , THNHM ), same data locality . Western : • 3 workers ( THNHM -I-00028941 , THNHM ), Kanchanaburi Province , Sai Yok District , Ban Chong Keab , dry dipterocarp forest , 25 May 2019 , W. Jaitrong leg. Northeastern : • 7 workers ( THNHM -I-00027315 , THNHM ), Nakhon Ratchasima Province , Wang Nam Kheao District , Sakaerat Environmental Research Station (ERS), dry dipterocarp forest , 14.5031 ° N , 101.9368 ° E , 5 June 2022 , W. Jaitrong leg., TH 22 - WJT- 264 ( THNHM ) ; Eastern : • 4 workers ( THNHM -I-00027316 , THNHM ), Chachoengsao Province , Tha Takiab District , 6 April 2003 , W. Jaitrong leg., WJT 260403-01 . Figure 2. Meranoplus siamensis sp. nov. (holotype, THNHM - I- 00027303 ) A head in full-face view B body in profile view C promesonotal shield in dorsal view D body in dorsal view. Measurements and indices. Holotype worker: HL 0.63, HW 0.65, ML 0.62, PML 0.48, PW 0.63, SL 0. 0.45, TL 2.58, CI 102.38, PMI 130.21, SI 69.77. Paratype workers ( n = 5): HL 0.60–0.65, HW 0.63–0.66, ML 0.60–0.65, PML 0.46–0.51, PW 0.62–0.65, SL 0.43–0.48, TL 2.56–2.82, CI 100–106.45, PMI 127–136.26, SI 67.72–71.97. Description of worker. Head in full-face view subquadrate, slightly shorter than broad, with sides broadly convex, posterior margin distinctly convex, posterolateral corner bluntly angulate. Antennal scapes short, reaching level of posterior margin of compound eyes, apical half incrassate; antennal segment II slender, longer than each of segments III – VI, and almost as long as III + IV + V; segment VI broader than each of segments II – V. Clypeus roughly subrectangular, shorter than broad, its anterior margin feebly concave medially, while posterior clypeal margin almost straight. Mandibles subtriangular, masticatory margin with four teeth. Compound eyes large and convex when seen in full-face view, located laterally and well behind mid-length of head, with 8 or 9 ommatidia along longest axis, each facet hexagonal (Fig. 6 A ). Frontal lobes broad, its anterior corners right angled and lateral margin almost straight (Fig. 5 H ). Frontal carinae long reaching posterolateral corners of head. Mesosoma in dorsal view, promesonotal shield distinctly shorter than broad, its lateral margin convex, serrate, margined and slightly overhanging mesosoma; lateral and posterior portions of promesonotal shield with translucent fins; posterior margin of promesonotal shield sinuate and distinctly concave; anterolateral corners of promesonotal shield bluntly angulate and posterolateral corners of promesonotal shield roundly angulate; promesonotal shield with two pairs of fenestrae laterally; metanotal groove absent. Declivity of propodeum almost invisible from above, mostly overhung by posterior margin of promesonotal shield (propodeal spines are visible in profile). Mesosoma in profile subquadrate, dorsal outline weakly convex, lateral face of mesosoma relatively flat; lateral portion of pronotum subtriangular; metapleuron not clearly demarcated from mesopleuron and lateral face of propodeum. Propodeal spines long and acute, longer than wide at its base, located at middle of propodeal declivity length. Petiole in profile subtriangular. Subpetiolar process low, its ventral outline weakly convex, with small anterior denticle. Postpetiole in profile subquadrate, shorter than high; in dorsal view, distinctly shorter than broad, anterior margin weakly convex, posterior margin distinctly convex; dorsum of postpetiole somewhat flat, marginated with distinct ridge, posterior face convex. Gaster about as large as head and mesosoma combined; first gastral tergite largest, in dorsal view, its anterior margin distinctly concave. Sculpture. Mandibles striate, shiny. Antennal scapes superficially striate. Head dorsally sparsely reticulate-rugulose laterally, while median portion weakly sculptured; half posterior portion of antennal scrobes shagreened mixed with few transverse ridges. Promesonotal shield more weakly sculptured than dorsum of head, with median portion smooth, shiny, and lacking any rugae; in profile, upper one-third portion of pronotum shagreened, while lower two-third portion with sparse irregular ridges; upper one-third portion of mesopleuron shagreened, lower two-thirds longitudinal weakly striate; metapleuron, and lateral faces of propodeum somewhat smooth and shiny. Propodeum declivity shagreened. Petiole smooth and shiny, postpetiole somewhat smooth but posterior face of postpetiole scabrous. First gastral tergite superficially shagreened with smooth and shiny interspaces. Pilosity and coloration. Dorsa of head and mesosoma with dense erect hairs mixed with sparse longer hairs; antennae with dense suberect hairs; in profile, lower two-thirds of pronotum with sparse suberect hairs; lower one-third of mesopleuron and metapleuron with sparse suberect hairs; area around propodeal spiracle with sparse suberect hairs; femora and tibiae with numerous long outstanding hairs as well; petiole with weakly sparse erect hairs on its anterior face and dorsum; postpetiole with dense long erect hairs, except anterior face without hairs; gaster with dense long erect hairs. Body mainly reddish brown; mandibles, antennae, legs, and tip of gaster yellowish brown. Distribution. Thailand ( Uthai Thani , Chonburi , Nakhon Ratchasima and Kanchanaburi Provinces, Fig. 4 ). Etymology. The specific name is after Thailand where the type locality is located; Thailand was called “ Siam ” in the past. Habitat. This species can be found in dry evergreen and dry dipterocarp forests. The specimens collected from northeastern Thailand (colony code TH 22 - WJT- 264) nested in the soil. Workers moved slowly on the ground. Differential diagnosis. Meranoplus siamensis sp. nov. is a small species that is most similar to Meranoplus tanomtongi sp. nov. in general appearance, having a pair of fenestrae along each lateral margin of the promesonotal shield, and having a subrectangular postpetiole when seen in profile. However, M. siamensis can be distinguished from M. tanomtongi by: 1) anterior corners of frontal lobes right angled and lateral margin almost straight (round and lateral margin weakly convex in M. tanomtongi , see Figs 5 E, H for comparison); 2) compound eyes with 8 or 9 ommatidia along longest axis, each facet hexagon (each facet round or elliptical in M. tanomtongi , see Figs 5 G , 6 A for comparison); 3) dorsum of head weakly sculptured (dorsum of head entirely and distinctly reticulate in M. tanomtongi , see Fig. 5 F, I for comparison); 4) dorsum of postpetiole somewhat flat, marginated with distinct ridge (shallowly concave, marginated with distinct ridge in M. tanomtongi ); 5) entire head with dense short hairs mixed with sparse longer hairs (hairs along head margin clearly longer than hairs on middle of head in M. tanomtongi , see Fig. 5 F, I for comparison). The type series of M. siamensis sp. nov. is very similar to the non-type specimens from Central Thailand (TH 02 - WJT- 039). However, the two colonies have some variations: 1) compound eyes with 9 ommatidia along longest axis in the type series (8 ommatidia in colony no. TH 02 - WJT- 039); 2) promesonotal shield shorter than broad in the type series (almost as long as broad in colony no. TH 02 - WJT- 039); 3) posterior half of head with sparse and weak reticulation in the type series (dense distinct reticulations in colony no. TH 02 - WJT- 039); 4) propodeal declivity somewhat shagreened in the type series (smooth and shiny in colony no. TH 02 - WJT- 039); 5) first gastral tergite superficially shagreened with smooth and shiny interspaces in the type series (distinctly shagreened in colony no. TH 02 - WJT- 039). These characters are not clear enough to distinguish the two populations.