Myopias minima, Jaitrong & Tasen & Guénard, 2018

Jaitrong, Weeyawat, Tasen, Wattanachai & Guénard, Benoit, 2018, The ant genus Myopias Roger, 1861 (Hymenoptera: Formicidae: Ponerinae) in Thailand, with descriptions of three new species, Zootaxa 4526 (2), pp. 151-174 : 162-165

Myopias minima sp. nov.

( Figs. 28–33 )

Etymology. The species epithet “ minima ” is a Latin word meaning minimum. This refers to this species being the smallest within the described species of the genus.

Type. Holotype worker (THNHM-I-00242, THNHM), S Thailand, Pattalung Prov. , Sribanpot Dist. , Riang Thong Waterfall, 7.70782500°N, 99.81130000°E, Rotting wood, 250 m alt., 24.VIII.2002, W. Jaitrong leg., Colony no. WJT07-TH-2041 . Paratypes: two workers (THNHM-I-00243 and THNHM-I-00244, THNHM) and 1 queen (THNHM-I-0 0 245, THNHM), same colony as holotype .

Diagnosis of worker: This is currently the smallest Myopias species. Masticatory margin with four teeth, including large basal tooth, large prebasal tooth, minute preapical tooth (denticle), and medium-sized apical tooth; basal margin with a well-defined protuberance; median clypeal lobe very short, clearly shorter than broad, broadest posteriorly, its anterior margin straight; eyes absent; frontal lobes high, not passing over anterior clypeal margin; with head in full-face, antennal scapes not reaching posterior margin of head; petiole in profile subrectangular, slightly longer than high; subpetiolar process well developed, subtriangular, apex of subpetiolar process truncate and directed downward, anterior margin convex, while posterior margin almost straight and distinctively longer. Entire body (head, mandible, antennal scape, mesosoma, legs, petiole and remaining metasoma segments) smooth and shiny. Body entirely reddish o yellowish brown, normally head darker than elsewhere.

Worker description (figs. 31–33)

Measurements. Holotype: TL 4.30, HL 0.83, HW 0.70, SL 0.56, ML 0.46, PW 0.50, MSL 1.16, PL 0.33, PH 0.45, DPW 0.31; CI 84, SI 80, MI 56, LPI 135, DPI 95.

Paratype workers (n = 2): TL 4.10–4.31, HL 0.82–0.83, HW 0.69–0.72, SL 0.52–0.55, ML 0.46–0.53, PW 0.51–0.53, MSL 1.16–1.21, PL 0.31–0.36, PH 0.45–47, DPW 0.33–0.35; CI 84–88, SI 75–76, MI 56–63, LPI 131– 145, DPI 97–106.

Head: In full-face view head clearly longer than broad (CI= 83–84), subrectangular with sides convex and posterior margin weakly concave; posterolateral corners of head bluntly angulate. Mandibles robustly linear and subfalcate, relatively short, down-curved in profile; masticatory margin with four teeth, including large basal tooth, large prebasal tooth, minute preapical tooth (denticle), and medium-sized apical tooth; basal margin with a welldefined protuberance; distance from prebasal tooth to preapical tooth about half of distance from basal tooth to prebasal tooth (fig. 2). Median clypeal lobe very short, clearly shorter than broad, broadest posteriorly, its anterior margin straight. Eyes absent. Antennal scapes robust and enlarged toward their apical portion to reach nearly the width of a frontal lobe, extending posteriorly not reaching posterior margin of head; antennal segment II longer than broad and longer than each of segments III–VIII; segments III–VIII each shorter than broad; four apical segments forming a club. Frontal lobes long and broad, slightly translucent, low slightly extend over anterior margin of clypeus. Median longitudinal frontal sulcus deep, extending slightly beyond 1/3 of head length.

Mesosoma: Stout, in profile with weakly convex dorsal outline, mesonotum anteriorly raised slightly higher than pronotum and propodeum; promesonotal suture and metanotal groove distinct; mesopleuron clearly demarcated from metapleuron by a deep groove; metapleuron not demarcated from lateral face of propodeum; pronotum slightly broader than mesonotum and propodeum in dorsal view; mesonotum about 2/3 length of pronotum in dorsal view.

Metasoma: Propodeum with almost straight dorsal outline, sloping gradually to propodeal junction; propodeal junction obtusely angulated; declivity of propodeum more or less flat. Petiole in profile subrectangular and sessile, longer than high, its anterior face vertical, dorsal and posterior faces weakly convex; in dorsal view petiolar node subrectangular, slightly wider than long (DPI 100–105), broader posteriorly; subpetiolar process well developed, subtriangular, apex of subpetiolar process truncate and directed downward, anterior margin convex, while posterior margin almost straight and distinctively longer. Metasomal segments III to IX elongate, in dorsal view, metasomal segment III slightly narrower than IV. Sting long, sharp and upcurved.

Entire body (head, mandible, antennal scape, mesosoma, legs, and metasoma) smooth and shiny. Pilosity comparatively sparse; dorsa of head, mesosoma, and metasoma with sparse standing hairs mixed with sparse shorter hairs; tip of metasoma with dense standing hairs; tibiae with dense decumbent hairs. Body entirely reddish brown to yellowish brown, head darker than elsewhere.

Dealate queen description (figs. 31–33)

Measurements. Paratype (dealate queen): TL 4.87, HL 0.91, HW 0.85, ED 0.30, SL 0.60, ML 0.59, PW 0.69, MSL 1.54, PL 0.44, PH 0.62, DPW 0.46, CI 94, SI 70, OI 35, MI 65, LPI 140, DPI 106.

Similar to the worker in structure, sculpture and pilosity, with the following conditions that should be noted: body clearly larger; head in full-face view slightly longer than broad, rectangular, with parallel sides and concave posterior margin; eyes large, almost as long as the apical segment of antenna; distance between eye and mandibular base much shorter than eyes length; median ocellus as large as lateral ocelli; mesoscutum trapezoidal with slightly protruding borders, anterior edge convex in dorsal view; in profile, its anterior portion slightly bulged and flattened caudad; parapsidal lines indistinct; scutellum oblong, clearly broader than long; metanotum very short; metanotalpropodeal sulcus deeply impressed; propodeal outline almost straight; propodeal junction nearly right-angled; petiole clearly shorter than high; metasoma (segments III to IX) relatively larger than in the worker.

Head, pronotum, mesopleuron, metapleuron, propodeum, petiole, metasoma segments III and IV reddish brown; mesoscutum, scutellum, tip of metasoma and legs yellowish brown; antenna and mandible lighter than head but darker than legs.

Habitat. The type series of M. minima was found nesting inside a small dead branch in an advanced stage of decomposition on the forest floor of a lowland rainforest.

Distribution. This species is known only from the type locality (S Thailand, Pattalung Province, fig. 52).

Comparative notes. Myopias minima can be distinguished from the closely related species, M. bidens ( Emery, 1900) ; M. breviloba (Wheeler, 1919) ; M. castaneicola (Donisthorpe, 1938) ; M. chapmani Willey & Brown, 1983 ; M. daia Xu et al., 2014 ; M. darioi Probst et al., 2015 ; M. luoba Xu & Liu, 2011 ; M. mayri (Donisthorpe, 1932) and M. trumani (Donisthorpe, 1949) by the following characteristics: eyes clearly absent in the worker (compound eyes reduced with ca. 5 facets, or larger in closely related species); median clypeal lobe very short, distinctively shorter than broad, broadest posteriorly (similar to that of M. breviloba ), its anterior margin straight (anterior margin concave in M. breviloba ); smallest species among the closely related species (worker’s HW 0.69–0.72 mm in M. minima ; over 0.79 in other species). Myopias minima is also closely related to M. nops Willey et Brown, 1983 from Taiwan in having a small body size and lacking eyes in the worker caste. However, M. minima is easily separated from M. nops by the following characteristics: most of body smooth and shiny (reticulo-punctate in M. nops ); anterior margin of median clypeal lobe straight (concave in M. nops ); antennal scape extending posteriorly not reaching posterior margin of head (reaching posterior margin of head in M. nops ).

Figures

FIGURES 28–30. Myopias minima sp. nov. (Paratype worker, THNHM-I-00243); 28, Body in profile view; 29, body in dorsal view; 30, head in full-face view.

FIGURES 31–33. Myopias minima sp. nov. (paratype queen, THNHM-I-00245); 31, Body in profile view; 32, body in dorsal view; 33, head in full-face view.