Atopomyrmex

Hita Garcia, Wiesel and Fischer (2013) - Atopomyrmex is endemic to the Afrotropical zoogeographical region and with only three species is a relatively small genus. Nevertheless, the distribution of the genus extends to much of Sub-Saharan Africa. Atopomyrmex was revised by Bolton (1981a) who recognised two species, and a third was later described by Snelling (1992). Species identification can be easily performed with the species key from Bolton (1981a) and the diagnostic notes in Snelling (1992). Atopomyrmex are highly polymorphic, arboreal ants that nest in living wood (Bolton, 1981a; Kenne et al., 2009). From one species it is known that its wood-excavating nest activities cause the tree branches to dry out (Kenne et al., 2009). Atopomyrmex ants forage in the vegetation or on the ground and their diet is variable. It can consist of honeydew or small arthropods. In addition, they seem to prefer the canopy stratum of secondary forests or woodlands, but are only rarely encountered in old growth forests (Kenne et al., 2009; F.H.G. & G.F., unpublished data).

Identification
Bolton (1981) - The genus most closely related to Atopomyrmex is the Ethiopian and Malagasy genus Terataner. Differences separating them, and other related genera, are noted in the discussion of Terataner (p. 290). At its inception Atopomyrmex contained only Atopomyrmex mocquerysi. Soon afterwards Atopomyrmex cryptoceroides was added and this was followed by a number of others, added later by several authors. Later still these extra species were progressively removed from Atopomyrmex until the present time, when mocquerysi and cryptoceroides are again its only members. These species, originally described in Atopomyrmex but now placed elsewhere, are as follows. The species alluaudi Emery, bottegoi Emery, foreli Emery, luteus Emery, scotti Forel, and steinheili Forel were transferred to Terataner by Emery (1912); nodifier Emery was originally made type-species of genus Atopula Emery but is now included in [Tetramorium]] Mayr, see Bolton (1976; 1980); selebensis Emery was made type-species of Dilobocondyla Santschi, by Santschi (1910); escherichi Forel was transferred to Dilobocondyla by Forel (1913c); ceylonicus Emery was made type-species of Paratopula Wheeler, by Wheeler (1919).

Biology
Bolton (1981) - Atopomyrmex is a small genus of strongly polymorphic arboreal ants. The two species included, Atopomyrmex mocquerysi and Atopomyrmex cryptoceroides, nest in the wood of standing trees and forage arboreally, frequently coming down the trunk but only rarely venturing onto the ground. Arnold (1916) points out that mocquerysi is usually carnivorous and, when disturbed, exudes a whitish secretion from the anal glands. Nests are made in hollow stems or rotten parts of standing timber but it is not known if the species tunnel their own galleries or take over the galleries of termites and boring beetles. Of the two species mocquerysi is very widely distributed, being found in wooded and forested areas almost throughout sub-Saharan Africa; Wheeler (1922: 181) gives a distribution map. A. cryptoceroides has a more limited range, being confined to the rain-forest zones of west of central Africa, where it is sympatric with mocquerysi.

Worker Morphology
These characters are collated in the Worker Morphology table.

Nomenclature

 *  ATOPOMYRMEX [Myrmicinae: Formicoxenini]
 * Atopomyrmex André, 1889: 226. Type-species: Atopomyrmex mocquerysi, by monotypy.

Snelling (1992) - The following new species is at variance with the generic characterization provided by Bolton, and that characterization must now be modified. In the brief descriptive statements below, the character state as described by Bolton is indicated in parentheses.

Palpal formula 5,3 in all sizes (4,3). Antenna 9-segmented, with short, stout scape and thickly clavate flagellum (12-segmented, scape slender, flagellum longer and with distinct 3-segmented club). Pronotum hardly marginate at side (bluntly marginate). Promesonotal suture distinct across dorsum in small workers (obsolete in workers of all sizes). Mesonotum not tuberculate in profile (tuberculate) and larger workers without transverse impression at midlength (transverse impression present). Petiole without dorsal spine pair (spines present). Head and body with numerous standing hairs (standing hairs absent except on mouthparts, flagellum, and gastral sterna).

Bolton (1981) - Polymorphic arboreal myrmicine ants. Mandibles short and stout, the apical (masticatory) margin armed in smallest workers with 2 teeth followed by 2 denticles and an unarmed straight edge; in slightly larger workers the edge crenulate or feebly denticulate. Most medium-sized and large workers with 2 teeth + 4-5 denticles but in large workers all the teeth may be worn down and rounded. Palp formula 4, 3 in all sizes; in smallest workers the two basalmost maxillary palp segments may be partially fused. Median portion of clypeus shield-like, broad, posteriorly broadly inserted between the frontal lobes. Anterior clypeal margin indented to concave medially, the median portion separated from the lateral parts by a longitudinal carina on each side. Anterior tentorial pit represented by a deep and sharply incised hole which is roughly circular, situated immediately behind the clypeus close to the antennal insertions and more obvious in larger workers. Development of frontal carinae varying with worker size. In smallest workers short and only feebly divergent, ending in front of the level of the anterior margins of the eyes. In largest workers extending back beyond the level of the posterior margins of the eyes and strongly divergent from source to level of eyes; behind this roughly parallel. Workers between largest and smallest showing intermediate development of frontal carinae. Antennal scrobes absent in smallest workers, becoming longer and deeper with increasing size; conspicuous and capable of accommodating the scape in largest workers. Antennae 12-segmented with a 3-segmented club. With head in full-face view the eyes situated behind the midlength of the sides, and the occipital corners broadly and evenly rounded. Pronotum more or less flat to shallowly concave transversely, bluntly marginate laterally, the margination more acute in smaller workers. Promesonotal suture vestigial to absent from dorsum but at sides forming an impression separating pronotum and mesonotum. Mesonotum in profile usually broadly and bluntly bituberculate behind, then sloping almost vertically to the broad metanotal groove. In medium to large workers the mesonotum with a shallow but quite broad transverse impression at about the midlength. Propodeum in profile raised immediately behind the metanotal groove then sloping downwards to a pair of strong spines. Metapleural lobes inconspicuous, very narrow and low. Propodeal spiracle circular. Lower margin of metapleuron without a broad groove running forward from the orifice of the metapleural glands; instead the margin rounded and folded under, giving the appearance of being smoothly eroded away, the hind coxa appearing to rest upon the bulla of the metapleural gland. Ventral surface of alitrunk with a very conspicuous roughly circular deep pit between the hind coxae, a sieve-plate apparently present at the bottom of the pit. Petiole dorsally with a pair of short stout spines of variable size. Dorsal surfaces of head and body without standing hairs, such hairs present only on mouthparts and gastral sternites.