Nesomyrmex angulatus

An arid habitat species predominantly found on the trunk of trees or the lower vegetation, rarely on the ground. It nests in pre-existing cavities of dead wood.

Identification
Hita Garcia et al. (2017) - The following character combination distinguishes N. angulatus from the other members of the group: in profile mesosomal dorsum forming a single, uninterrupted flat surface without any trace a of metanotal groove; petiolar peduncle short; body colour yellow to very light brown.

Nesomyrmex angulatus together with Nesomyrmex grisoni are easily separable from the other members of the group on the basis of the dorsal mesosomal outline, which is an uninterrupted, flat surface without any trace of a metanotal groove. The separation of N. angulatus from N. grisoni is less clear though. As Bolton (1982) stated in his revision, the only differentiating character is body colour, which is yellowish in N. angulatus and dark brown to black in N. grisoni. In general, body coloration is a rather weak diagnostic character and extremely variable in many ant species, and it is likely that both species are actually conspecific and the differently coloured forms represent geographic or ecological variants. The latter seems probable if one considers that N. angulatus is predominantly an arid-adapted species, while N. grisoni appears to prefer humid rain forests. Nevertheless, at the moment we hesitate to synonymise the two species and prefer to keep them separate for the following reasons. First, while there is a lot of material of N. angulatus in many museums, there is not much of N. grisoni, making comparative analyses challenging.

Csősz and Fisher (2016) - Workers of N. angulatus can be convincingly separated from those of Nesomyrmex clypeatus based on the lack of median clypeal notch in the former species. Nesomyrmex angulatus differs from species of bidentatus-complex and devius-complex (Nesomyrmex devius, Nesomyrmex exiguus, Nesomyrmex fragilis, Nesomyrmex gracilis and Nesomyrmex hirtellus) by having sharp anterolateral pronotal angles and a numeric key, FRS/CS ratio yields perfect separation between workers of N. angulatus and members of bidentatus-complex.

Sharaf et al. (2017)  Arabian Peninsula - The following character combination distinguishes N. angulatus from the other members of the group in the Arabian Peninsula: third mandibular tooth relatively larger and better developed; anterior clypeal lobe always conspicuously de-veloped, convex and rounded, never with a small median triangular projection; clypeus with median longitudinal carina; pronotum anterodorsally without sharp, dentate corners; in profile mesosomal dorsum forming a single, uninterrupted flat surface without any trace of metanotal groove; petiole with very well developed node.

This species exhibits remarkable variability throughout its distributional range, most notably in the shape of the petiolar node (Bolton 1982, Hita Garcia et al. 2017), but it is also relatively variable in body size and eye size. It is likely that the material currently understood to be N. angulatus is actually a complex of cryptic species.

Distribution
Hita Garcia et al (2017) - This species has by far the widest distribution range within the N. angulatus group, and likely represents the most widespread Nesomyrmex species on a global scale. It is found in the majority of African countries, as well as on the Arabian Peninsula and in most of the Malagasy region.

Csősz and Fisher (2016) - In the Malagasy zoogeographical region, this species is known to occur in coastal dry forests, mangroves and the coastal scrub of the northern, dry area of Madagascar and on adjacent islands in the Mozambique channel. Worldwide, N. angulatus has spread to the eastern Africa and the Middle East.

Distribution based on Regional Taxon Lists
Afrotropical Region: Botswana, Comoros, Djibouti, Eritrea, Ethiopia, Ghana, Kenya, Malawi, Mozambique, Niger, Nigeria, Saudi Arabia, South Africa, Sudan, Uganda, United Republic of Tanzania, Yemen, Zimbabwe. Malagasy Region: Madagascar, Mayotte, Seychelles. Palaearctic Region: Algeria, Egypt, Israel, Libya, Oman, Tunisia.

Habitat
Hita Garcia et al (2017) - Nesomyrmex angulatus has been collected from a variety of habitat types, such as tropical dry forest, coastal scrub, mangrove forest, savannah, and Acacia woodland. In general it seems as if the species prefers comparatively arid environments.

Biology
Hita Garcia et al (2017) - Nesomyrmex angulatus seems to prefer comparatively arid environments. In addition, it is predominantly found on the trunk of trees or the lower vegetation, rarely on the ground, and it nests in pre-existing cavities of dead wood (Bolton 1982; Mbanyana & Robertson 2008).

Bolton (1982) - Arnold (1916: 259) noted that he only found angulatus on the trunks of trees but personal observation has shown that it also occurs in leaf litter samples and log mould. However, the species does seem to prefer to nest clear of the ground when possible, as colonies are often found in West Africa in cocoa pods which are still attached to the tree, and a sample from Malawi was collected in Swartzia pods.

Collingwood and Agosti (1996) - The species was found in Yemen in partially rotten branches.

Nomenclature

 *  angulatus. Leptothorax angulatus Mayr, 1862: 739 (w.) EGYPT. Santschi, 1914b: 107 (q.). Combination in L. (Goniothorax): Emery, 1896g: 58 (footnote); in Nesomyrmex: Bolton, 2003: 272. Senior synonym of concolor, ilgii, latinodis: Bolton, 1982: 324. See also: Mbanyana & Robertson, 2008: 38. Current subspecies: nominal plus lybica.
 * ilgii. Leptothorax angulatus r. ilgii Forel, 1894b: 82 (w.) ETHIOPIA. Santschi, 1912c: 148 (q.). Combination in L. (Goniothorax): Wheeler, W.M. 1922a: 891. Junior synonym of angulatus: Bolton, 1982: 324.
 * concolor. Leptothorax angulatus var. concolor Santschi, 1914b: 107, fig. 15 (w.) KENYA. Emery, 1915g: 16 (q.m.). Junior synonym of angulatus: Bolton, 1982: 324.

Hita Garcia et al. (2017) - We are not fully convinced that all the material currently listed and identified as N. angulatus represents the same species. On the basis of some recent collections from Kenya and Mozambique we were able to observe a lot of morphological variation within and between localities. As already noted by Bolton (1982), the shape of the petiolar node seems to be especially variable. Consequently, we cannot rule out the possibility of dealing with a complex of more or less cryptic species. At the same time it is possible that N. angulatus is not only a very successful and widespread, but also an extremely variable species. The solution to this problem is not the aim of this study, since it requires the accumulation of an extensive amount of material from all over Africa, the Arabian Peninsula, and the Malagasy region.

Worker
Csősz and Fisher (2016) - Body color: yellow; brown. Body color pattern: concolorous; only clava darker. Absolute cephalic size (mm): 688 [630, 724], (nD33). Cephalic length vs. maximum width of head capsule (CL/CWb): 1.258 [1.218, 1.327]. Postocular distance vs. cephalic length (PoOc/CL): 0.371 [0.359, 0.386]. Postocular sides of cranium contour frontal view orientation: converging posteriorly. Postocular sides of cranium contour frontal view shape: feebly convex. Vertex contour line in frontal view shape: straight; feebly convex. Vertex sculpture: main sculpture rugoso-reticulate, ground sculpture areolate. Gena contour line in frontal view shape: convex. Genae contour from anterior view orientation: converging; strongly converging. Gena sculpture: rugoso-reticulate with areolate ground sculpture. Concentric carinae laterally surrounding antennal foramen count: present. Eye length vs. absolute cephalic size (EL/CS): 0.280 [0.262, 0.317]. Frontal carina distance vs. absolute cephalic size (FRS/CS): 0.325 [0.310, 0.343]. Longitudinal carinae on median region of frons: present. Smooth median region on frons: absent. Antennomere count: 12. Scape length vs. absolute cephalic size (SL/CS): 0.818 [0.783, 0.866]. Facial area of the scape absolute setal angle: setae absent, pubescence only. Median clypeal notch: absent. Ground sculpture of submedian area of clypeus: smooth. Median carina of clypeus: present. Lateral carinae of clypeus: present. Median anatomical line of propodeal spine angle value to Weber length in lateral view: 58-62°. Spine length vs. absolute cephalic size (SPST/CS): 0.273 [0.225, 0.304]. Minimum spine distance vs. absolute cephalic size (SPBA/CS): 0.325 [0.299, 0.354]. Apical spine distance vs. absolute cephalic size (SPTI/CS): 0.334 [0.294, 0.360]. Propodeal spine shape: straight; curving upward. Anterolateral pronotal corner: present. Apical distance of pronotal spines vs. absolute cephalic size (PSTI/CS): 0.690 [0.584, 0.736]. Metanotal depression: absent. Dorsal region of mesosoma sculpture: rugulose with areolate ground sculpture. Lateral region of pronotum sculpture: areolate ground sculpture, superimposed by dispersed rugae. Mesopleuron sculpture: areolate ground sculpture superimposed by dispersed rugulae. Metapleuron sculpture: areolate ground sculpture superimposed by dispersed rugulae. Petiole width vs. absolute cephalic size (PEW/CS): 0.410 [0.376, 0.445]. Dorsal region of petiole sculpture: ground sculpture areolate, main sculpture rogoso-reticulate. Postpetiole width vs. absolute cephalic size (PPW/CS): 0.488 [0.443, 0.546]. Dorsal region of postpetiole sculpture: ground sculpture areolate, main sculpture dispersed rugose.

Bolton (1982) - TL 3.1-3.8, HL 0.70-0.90, HW 0.56-0.74, CI 75-85, SL 0.50-0.66, SI 88-97, PW 0.40-0.56, AL 0.82-1.08 (65 measured).

Mandibles delicately but densely longitudinally striate, the striation usually distinct but sometimes superficial. Median clypeal lobe extensive, broad, covering the bases of the mandibles and having its anterior margin conspicuously arched-convex. Median clypeal carina fine, not strongly developed but usually discernible, only rarely the carina partially or wholly effaced. Antennal scrobes absent. Frontal carinae absent but in some the frontal lobe followed on one or both sides by a weak rugular line which runs back on the head. Maximum diameter of eyes 0.17-0.22, about 0.27-0.33 x HW and with 13 or more ommatidia in the longest row. With the head in full-face view the sides narrower in front of the eyes than behind, slightly convergent anteriorly. Sides of head behind eyes shallowly convex, slightly convergent posteriorly and meeting the occipital margin in a blunted angle. Occipital margin transverse to very shallowly concave, with a slightly projecting rim above the occipital foramen which is visible in full-face view. With the alitrunk in profile the dorsum forming a single shallowly convex to almost flat surface, without trace of a metanotal impression. Propodeum armed with a pair of triangular teeth or short broad spines of variable size. In general the teeth are about as long as their basal width and slightly upcurved, but individuals with spines longer than their basal width are fairly common. Specimens with the propodeal armament reduced to short broad teeth, where they are shorter than the basal width, are less common. Metapleural lobes low and rounded. In dorsal view the alitrunk with angulate to weakly dentate pronotal corners. Mesonotum narrower than pronotum and the sides of the propodeum diverging to the level of the spiracle and then converging to the bases of the propodeal teeth. Petiole in profile shaped as in Fig. 8, with a short anterior peduncle which has a triangular dentiform anteroventral process. Dorsal surface of peduncle with a denticulate process in front of the level of the spiracle on each side. Anterodorsal angle of node quite sharply defined, the posterodorsal angle much broader and bluntly rounded. Petiole node in dorsal view variable in shape and size. Usually the node about as broad as long, rarely slightly longer than broad but quite commonly obviously broader than long, in some cases approaching the postpetiole in width. Dorsum of head covered with a fine dense reticulate-punctulate ground-sculpture which in some samples is superficial and granular in appearance. Superimposed on this are very fine irregular rugulae which frequently form a narrow reticulum occipitally and sometimes also on the sides of the head. Dorsal surfaces of alitrunk, petiole and postpetiole with fine granular or punctulate ground-sculpture and with disorganized fine rugulae. The rugular sculpture is usually distinctive but in some individuals may be partially effaced. Base of first gastral tergite generally with a superficial reticular pattern but sometimes almost completely smooth. All dorsal surfaces of head and body with numerous short stout blunt hairs; such hairs absent from the appendages. Colour yellow, frequently with the antennal club darker.

Mbanyana and Robertson (2008) - HL 0.672–0.811, HW 0.565–0.692, HW1 0.610–0.736, CI 78–87, SL 0.487–0.613, SI 84–92, PW 0.423–0.541, ML 0.785–1.087, EL 0.169–0.197, EI 28–30 (5 of 81 measured).

Description matches that of Bolton (1982) except for few additional characters. Sculpture on the dorsum of head is not only reticulate-punctulate but also with longitudinal striations, which are well defined near the inner margin of the eyes.

Type Material
Csősz and Fisher (2016) - “Sinai”' [Egypt], collect. G.Mayr. Lectotype, designated by Bolton 1982: 324 (1w, CASENT0914922).

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