Amyrmex

This genus is only known from males and was once placed in the subfamily Dolichoderinae. Ward and Brady (2009), finding additional males in an existing collection, used molecular phylogenetics to place the genus in the Leptanilloidinae. Their study also suggested these ants could be males of Asphinctanilloides, a Leptanilloidinae genus only known from workers.

Identification
Ward and Brady (2009) provide the following list of distinctions between known males of Leptanilloides (Donoso et al. 2006; Ward 2007) and Amyrmex. One caveat is the mention by Ward and Brady that there are a number of undetermined male specimens, likely to be Amyrmex, that make these generic differences less certain.

Amyrmex


 * Small body size, HW 0.32–0.41, LHT 0.29–0.39
 * Scape shorter: SI 0.27–0.31; scape less than twice the length of the second antennal segment (SL/LA2 1.5–1.8)
 * Legs shorter, LHT/HL ~1.2
 * Paramere small, ~0.8× petiole length
 * Veins M and Cu diverging at crossvein cu-a
 * Submarginal cell elongate: about four times longer than wide, longer than the basal cell, extending distad of stigma and terminating in an acute point
 * No free M vein after Rs+M

Leptanilloides
 * Variable body size, HW ~0.40–0.64, LHT 0.40–0.72
 * Scape disproportionately longer: SI 0.37–0.41; scape more than twice the length of second antennal segment (SL/LA2 ~2.2)
 * Legs disproportionately longer, LHT/HL ~1.5
 * Paramere large, ~1.5× petiole length
 * Veins M and Cu diverging distal to crossvein cu-a by a distance greater than the length of the crossvein
 * Submarginal cell less elongate: no more than three times longer than wide, shorter than the basal cell, and terminating at level of stigma
 * Free M vein after Rs+M (may be weak)

Distribution
Known from Argentina and Brazil.

Biology
Anecdotal observations suggest the Leptanilloidinae behave as army-ant like predators. These ants are likely to be largely subterranean, occasionally coming to the ground surface under debri (rocks, downed wood, etc.) while foraging or to allow mature sexuals (either males only or perhaps males and females) to leave their natal nest. Group predation, frequent colony migrations and synchronized brood cycles may also be part of their life history.

Castes
This genus is known only from males.

The description of Kusnezov (1953):

Macho. Ala anterior con tipo particular de nervadura y de conformacion, relativamente corta, ancha y con el apice bien redondeado. Celda radial abierta. Celda cubital cerrada, relativamente muy larga, con el extremo distal que forma angulo agudo. Sin celda discoidal. La nervadura basal con un codo bien acentuado y situado a poca distancia de la sub costa. El trozo distal de mf. bien distinto. La nervadura longitudinal anal forma un arco regular uniendose con M-CuA casi exactamente en el punto de separacion de Mf. y CuA. Ala posterior con 3-4 ganchos. Antenas de 13 articulos, largas (un poco menos largas, que el torax y abdomen juntos), con los articulos poco diferenciados, siendo el escapo tan o un poco menos largo que los dos primeros articulos del funiculo. Man- dibulas debiles, relativamente cortas, solamente con un diente apical y sin margen interior bien distinto. Frente convexa en forma regular, sin aristas frontales distintas. Fosetas antenales bastante grandes, circulares, bien limitadas. Torax con el mesonoto y escutelo muy convexos casi hemisfericos; la cara basal del epinoto pasa al declive formando una curva. Peciolo con un pedunculo corto y el nudo casi globular. Abdomen compuesto de 5 segmentos visibles, de los cuales el segundo es el mas largo de todos, siendo el primero relativamente corto. Volselas relativamente cortas con el apice redondeado.

The subsequent redescription by Ward and Brady (2009):

Head broader than long (CI 1.25-1.37), with large convex eyes that occupy the anterior two-fifths to one half of the sides of head (REL 0.43-0.57) (Figure 2); mandibles slender, elongate-triangular to sublinear, masticatory margin edentate and weakly differentiated from the unarmed basal margin; external margin of mandible curved basally, straight medially, and bent slightly mesad at apex (Figures 2, 4-5); mandible tips crossing at closure, mandible length subequal to eye length (ML/EL 0.88-1.10, ML/HW 0.35-0.41); genal teeth and hypostomal teeth lacking; clypeus short and transverse, bordered anteriorly by a thin clypeal lamella (apron); antennal sockets horizontal and exposed, and located close to the anterior clypeal margin; antenna 13-segmented, each segment longer than wide; scape of moderate length, SI 0.27-0.31; scape length subequal to or less than the length of ultimate antennal segment (SL/LA13 0.73-0.97), scape length 0.11-0.14* total length of antenna, less than twice the length of the second antennal segment (SL/LA2 1.50-1.78), and slightly more than half the combined length of the second, third and fourth antennal segments (SL/(LA2+LA3+LA4) 0.52-0.65); lateral ocelli separated from median ocellus by about their diameters.

Mesosoma with distinctive pronotum (Figure 3): U-shaped in dorsal view and reduced anteromedially to a thin horizontal strip, set well below the level of the dorsally protruding mesonotum; pronotum triangular in profile, with pointed posterior apex directed towards the wing base; mesonotum lacking notauli; parapsidal sutures very weakly impressed, barely discernable; axillae not meeting medially, connected by a narrow furrow; tegula very small and inconspicuous; mesopleuron lacking oblique transverse sulcus and hence not divided into anepisternum and katepisternum; mesoscutellum prominently bulging, as seen in lateral view; metapleural gland reduced and inconspicuous; propodeal spiracle small, circular, positioned at about midheight of propodeum and slightly posterior to the metanotum. Legs slender (LHT/HL ~1.2); mesotibia and metatibia each with a single short spur; tarsal claws lacking preapical tooth.

Wings with reduced venation (Figure 6); pterostigma present; forewing with elongate submarginal cell, four times longer than wide, and longer than basal cell; base of Rs weak, and absent in one species (Amyrmex BR02), resulting in confluence of the basal and submarginal cells; submarginal cell extending distad of stigma and terminating in an acute point; no free M vein after Rs+M; discal (medial) cell lacking, i.e., m-cu crossvein absent; A merging into cu-a, which curves anteriorly to join M+Cu at the point where veins M and Cu diverge, hence no free A vein distal to cu-a (Figure 6); hindwing lacking closed cells; anterior margin of hindwing with 1-4 hamuli; jugal lobe absent.

Metasoma slender in profile, obovate in dorsal view, widest at abdominal segment 5; abdominal segment 2 (petiole) subquadrate in profile (Figure 3), longer than high or wide, and only weakly constricted posteriorly, the helcium thus apparently quite broad; spiracle on abdominal segment 2 located on anterior third, near anterodorsal extremity; abdominal segment 3 larger than petiole, and not developed as postpetiole nor separated from abdominal segment 4 by a marked constriction; abdominal spiracle 3 located on anterior third of tergite; abdominal segments 2 and 3 with tergosternal fusion; abdominal segment 4 lacking tergosternal fusion; segment 4 with short but distinctly differentiated presclerites; spiracle present on anterior half of tergite 4; abdominal segments 5 and 6 lacking well differentiated presclerites, and not separated from succeeding segments by constrictions; abdominal spiracles 5 and 6 not discernable in specimens examined but possibly present at anterior margins of respective tergites; abdominal tergite 8 (pygidium) small and simple but visible dorsally, not wholly covered by abdominal tergite 7; cerci absent; subgenital plate (abdominal sternite 9) with posterior margin broadly concave but not bifurcate; basal ring not hypertrophied; paramere small and slender with rounded apex, paramere about 0.8* petiole length; volsella a simple, elongate-triangular lobe, lacking differentiated cuspis.

Body size very small; total length, excluding appendages, approximately 1.1-1.7 mm; HW 0.32-0.41, LHT 0.29-0.39; integument mostly smooth and shiny, with scattered piligerous punctures; pilosity common on most of body, suberect to decumbent. Color: body yellowish-brown to medium-brown, head and posterior margins of abdominal segments 4-7 darker, appendages (antennae, mandibles, legs) lighter.