Apterostigma megacephala

Collection data for all specimens indicate this species is found in lowland mesic forests. Although only four workers have been found, it is probably safe to assume that this species is monomorphic, given the small variation in measurements of the studied specimens and the basal position of the group within Attini. Only more derived attines, such as Acromyrmex and Atta, are polymorphic. (Lattke 1999)

Identification
Lattke (1999) - Flattened compound eyes partially wrapped around conical tubercles, ommatidia reduced; mesonotal denticles present; erect rigid pilosity present on head, mesosoma and gaster; erect hairs with spatulate apices frequently present on mesosoma.

Distribution based on Regional Taxon Lists
Neotropical Region: Colombia, Peru.

Nomenclature

 *  megacephala. Apterostigma megacephala Lattke, 1999: 2, figs. 1, 2 (w.) PERU.

Worker
Holotype (UNCB-CPDC paratypes): HL 1.69 (1.70-1.64); HW 1.44 (1.51-1.46); LW 0.90 (0.94-0.91); ML 0.90 (1.06-1.02); SL 1.47 (1.64-1.54); LM 2.49 (2.51-2.47) mm. CI 0.85 (0.89-0.89); SI 1.02 (1.09-1.05). Head in frontal view subquadrate, anterior clypeal border broadly convex, medially bluntly angulate or with blunt short denticle; sides slightly diverging posterad, posterolaterally convex and with straight posteromedian border. Clypeus anteriorly with narrow, longitudinal band of smooth and shiny integument, remainder opaque, rugose; prominent median seta usually present on anterior edge, thicker and longer than surrounding hairs. Clypeus medially with carinae forming Y-shaped ridge, each posterior arm stems from below frontal lobe, with anterior arm extending to posterior edge of shiny strip. Clypeus posterolaterally bound by ridge extending from frontal lobe, separating it from antennal fossae; each ridge then extends posterad, bordering antennal fossa laterally and joining rugae on cephalic dorsum just below level of eye. Frontal lobes relatively massive and subtriangular, with bluntly rounded apex, very short anterior margin, very broadly convex lateral margin and approximately straight posterior margin; dorsal surface with coarse longitudinally arching rugae. Frontal carinae extending posterad only to upper level of eyes, afterwards joining 2 posteromedian swellings that meet at midline to enclose dorsomedian cephalic depression. Compound eye on subconical tubercle, in lateral view forming ellipse curved around anterior half of tubercle; ommatidia fiat, separated from one another. Occipital lobes short, subquadrate, joined by posterodorsal low transverse ridge. Cephalic sculpturing opaque, coarsely rugose except finely granulose antennal fossae, ocular prominences and most of dorsomedian depression. Scapes transversely rugose, base strongly bent, with rigid decumbent hairs. Antennal fossae relatively large, reniform. Dorsal mandibular surface striate, smooth and shiny along chewing border and distad; chewing border with 8 widely spaced teeth, apical tooth largest. Palpal formula: 3: 1 or 3:2. In situ count. Transverse carina lacking on cervical area; pronotum with median longitudinal carina, laterally with more or less parallel rugulae. Lateral margins of propleura and pronotum evenly curved, without denticle or angle. Mesonotum with 4 denticles, anterior pair longer than posterior; neither promesonotal suture nor metanotal sulcus evident. Anepisternum with low rugae, dorsoposteriorly bound by brief carina; mesopleuron with short ventral carina at mesosomal constriction. Rugae on mesosoma not as broad and coarse as on head; sculpture finer with sparse rugulae. Mesometanotum without well defined longitudinal carinae. Mesosoma laterally with relatively straight anterior pronotal margin; margins of posterior pronotum and mesonotum form convexity interrupted by mesonotal denticles. Metanotum concave; dorsal propodeal face very broadly convex, almost straight, about twice as long as declivitous face. Propodeal dorsum with 2 posterior denticles; base of each propodeal denticle joined to inferior propodeal lobe by vertical carina. Mesopleuron with low anteriorly projecting ventral lobe, just dorsad of mesocoxa. Pronotal-mesopleural suture distinct, terminating dorsally at brief lobe overlapping mesothoracic spiracle; small tubercle present at apparent dorsal end of metapleura. Metapleura and lateral propodeal faces with finely granulose sculpturing, no rugae. Propodeal spiracle prominent, opening directed obliquely laterally. Dorsal propodeal surface forms slightly elevated rectangular surface bordered anterad by transverse carina and laterally by longitudinal carinae that end posterad at propodeal denticles. Convex propodeal lobes present. Petiole slightly pedunculate, node broadly convex, its posterolateral margins angulate and pointing obliquely posterad; low anteroventral lobe present. Petiolar and postpetiolar dorsum rugulose. Postpetiole laterally with convex anterodorsal margin; ventral margin straight, bound at each end by raised triangular margins; dorsal surface with posterolateral ridge ending in rounded lobe. First gastral segment with anterodorsal lobe, a continuous extension of gastral sculpturing partially overlapping constriction of helcium dorsally, apex bluntly pointed and base with modest but well-defined transverse concavity. Posterodorsal margin of postpetiole covers most of lobe. Gaster laterally subglobulose, dorsal margin evenly convex and ventral margin sharply convex; tergum of gastral segment I with rugulae forming almost areolate pattern, sternum with rugulae along posteromedian area, fading out towards base; low lateral longitudinal carinae present on tergum. Procoxae mostly smooth except for low rugulae towards apex, no rugulae on meso- and metacoxae. Apex of metacoxa with a sulcus along each side of insertion of trochanter, each sulcus divided into rounded cells. Body without pubescence except on antennal flagella, protibiae and tarsi. Hairs on mesosoma rigid and frequently capitate, those on gaster slender and subdecumbent; head with sparse depressed hairs; vertex and occiput with erect to suberect rigid hairs. Body brown, mandibular masticatory border black.

Type Material
Holotype. Peru, Madre de Dios, Cuzco Amazonico, 15 km NE Puerto Maldonado, Rio Tambopata, 200 m, 21-VI-89, S.P. Cover, J.E. Tobin, leg. CA-357. Plot IE 24. Worker deposited in. Paratypes. (1) Peru, Madre de Dios, Estacion Pakitza-Manu, 13-17/02/92, R. Combra, D. Quintero leg. Worker deposited in. (2) Colombia, Meta, Parque Natural Nacional La Macarena, IX-90, M.T. Barreto leg. Worker deposited in. (3) PERU, Madre de Dios, Manu Reserve Zone, Pakitza Station. X-88. J. Tobin leg. Worker deposited in.

F. Fernandez has supplied additional data about the locality for the Colombian specimen: “primary forest between Rfos Duda and Guayabero, some kilometres west of the town La Macarena, 350 m.”

Etymology
The species name is derived from the Greek words for large, mega, and head, kephale. It alludes to the prominent head.

References based on Global Ant Biodiversity Informatics

 * Fernández, F. and S. Sendoya. 2004. Lista de las hormigas neotropicales. Biota Colombiana Volume 5, Number 1.
 * Lattke, J.E. 1999. A new species of fungus-growing ant and its implications for attine phylogeny (Hymenoptera: Formicidae). Systematic Entomology 24:1-6
 * Schultz T. R., J. Sosa-Calvo, S. G. Brady, C. T. Lopes, U. G. Mueller, M. Bacci, and H. L. Vasconcelos. 2015. The most relictual fungus-farming ant species cultivates the most recently evolved and highly domesticated fungal symbiont species. The American Naturalist (in press).
 * Solomon S. E., C. Rabeling, J. Sosa-Calvo, C. Lopes, A. Rodrigues, H. L. Vasconcelos, M. Bacci, U. G. Mueller, and T. R. Schultz. 2019. The molecular phylogenetics of Trachymyrmex Forel ants and their fungal cultivars provide insights into the origin and coevolutionary history of ‘higher-attine’ ant agriculture. Systematic Entomology 44: 939–956.