Xymmer

There are two known species in this genus, the West African Xymmer muticus is a ground dwelling species of rainforest and savannah habitats while the Southeast Asian Xymmer phungi has been found in a lowland evergreen forest nesting under a wood fragment on the forest floor.

Identification
The worker mandibles, shape of the head and general body form are most similar to Amblyopone, Prionopelta and Stigmatomma.

Nomenclature

 * XYMMER [Amblyoponinae]
 * Xymmer Santschi, 1914d: 311 [as subgenus of Stigmatomma]. Type-species: Stigmatomma (Xymmer) muticum, by monotypy.
 * Xymmer raised to genus: Wheeler, W.M. 1922a: 641 (in key).
 * Xymmer subgenus of Amblyopone: Clark, 1934b: 27.
 * Xymmer junior synonym of Stigmatomma: Brown, 1949c: 87.
 * Xymmer junior synonym of Amblyopone: Brown, 1960a: 155.
 * Xymmer revived from synonymy, status as genus: Yoshimura & Fisher, 2012: 19.

Epistome inerme avance en lobe rectangulaire. Mandibules etroites avec une rangee de dents simples tout le long de leur bord interne. Thorax etroit a suture promesonotale distincte, les autre absolete. Pedicule etroit, assez longuement petiole en avant, gastre etrangle et tres allonge, pour le reste comme chez Stigmatomma.

Yoshimura and Fisher (2102) - We resurrect Xymmer here as an independent genus from a synonymy with Amblyopone based on a morphological examination of males of nine morphospecies. Males of Xymmer can be distinguished from other amblyoponine males in the Malagasy region by a lack of dent-like projections on the anterior margin of the clypeus. In addition to this unique character, Xymmer can be separated from Adetomyrma by fewer mesotibial spurs (two in Adetomyrma, 0–1 in Xymmer), absence of the pygostyles, and abdominal sternum IX convex distally; from Stigmatomma by lack of the pygostyles, the radial sector on the forewing between Rs+M and 2r-rs, the media on the hindwing apical to the cubitus, and 1rs-m on the hindwing; from Mystrium by a lack of the frontal carinae, radial sector on forewing partially absent, an absence of 1rs-m, and media apical to cubitus on hindwing; from Prionopelta by a lack of the frontal carinae, having a distinct epimeral lobe, lack of pygostyles, and lack of a vein on hindwing between radial sector and cubitus. The mesotibial spur may be useful as a separable character: the spur is absent in most males of Xymmer (only X. mgm01 has the spur on the mesotibia out of the nine morphospecies examined), while at least a single spur is present in all males of Stigmatomma.

Few morphological discussions exist regarding the taxonomic status of the name Xymmer. Xymmer was described by Santschi as a monotypic subgeneric taxon under Stigmatomma [43]. Since Santschi’s original description, Xymmer was raised to genus by Wheeler in his identification key for African Amblyoponini [7]. Clark regarded Xymmer as a subgenus in Amblyopone [45] following Wheeler’s suggestion [46]; however, distinguishing characters were not discussed in their treatments. Brown [9,17] discussed separable characters for Xymmer (as a junior synonym under the subgenus Stigmatomma) for the first time since Santschi’s original description. Brown regarded Stigmatomma and its related names as junior synonyms of Amblyopone at that time [9], and this treatment constituted the recent concept of the genus Amblyopone.

We decided that the male characters proposed and associations between the worker lectotype and our materials are sufficient to warrant designating Xymmer as an independent genus from Amblyopone. Santschi’s description [43] misidentifies the criterion for separating Xymmer from Amblyopone as having conical setae just present or absent, as discussed in Brown ([9]: p.165). Although Santschi proposed a lack of conical setae on the anterior clypeal margin in workers as a diagnostic character [43], this description did not provide enough information on the uniqueness of the character observed in Xymmer. Our examination of the lectotype of Stigmatomma (Xymmer) muticum found a distinct plate-like projection just dorsal to the junction between the clypeus and labrum, and the projection widens distally with a flat distal margin (Figure 14C). This projection seems to be located along a line slightly ventral to where the conical setae are arranged (Figure 14D), and could replace the function of the conical setae; therefore, it is different from a typical mid-clypeal projection in Amblyopone, which bears the conical setae on its anterior margin. This specialized projection in Xymmer should be emphasized as a unique character to differentiate Xymmer from Amblyopone and Stigmatomma. The same clypeal character observed in the lectotype of S. (X.) muticum was found in some worker specimens in the Malagasy region, and we confirmed that male specimens identified as Xymmer (e.g. CASENT0007085) were congeneric with worker specimens identified as Xymmer (e.g. CASENT0007090) (unpublished COI sequence data). The Malagasy workers have a ‘‘mutica-like’’ clypeal character.

Male With characters of Amblyoponinae. Frontal carinae absent. Anterior margin of clypeus flat, without dent-like projections. Antenna consisting of 13 segments. Mandible with single tooth, apex sharp or blunt (Figure 12E). Palpal formula 3,3 (Figure 13E)/3,2/4,3, one specimen each of six morphospecies dissected. Notaulus distinct (Figure 3E). Mesepimeron with distinct posterodorsal lobe (epimeral lobe: Figure 2E). Mesotibia without spur in most cases, with single spur in one species. Metatibia with two spurs. In dorsal view, distinct constriction present between petiole and abdominal segment III. Abdominal segment IV with tergosternal fusion. Pretergite of abdominal segment IV distinctly differentiated from posttergite; a deep transverse furrow divides them. Pygostyles absent.

Distal margin of abdominal sternum IX convex (Figure 7E). Separation between basimere and harpago distinct. Basal projection on cuspis well-developed (Figure 9E). Basicoventral portion of aedeagus not extraordinarily expanded (Figure 8E). Aedeagus in lateral view, serrate denticles present on basal portion of its ventral margin.

On forewing (Figure 10E), pterostigma well-developed, radial sector absent between M+Rs and 2r-rs, radial sector reaches to costal margin, 2r-rs connected with radial sector posterior to pterostigma, 2rs-m present, cu-a located far from junction between media and cubitus in most cases, located close to junction in one species. On hindwing (Figure 11E), Sc+R1 and radius (R1) absent, 1rs-m absent, media absent apical to 1rs-m.