Tetramorium akengense

Only known from the type specimens (workers) collected in central Africa.

Identification
Tetramorium akengense is straightforwardly recognizable in the muralti complex with the following character combination: anterior clypeal margin medially impressed; petiolar node squamiform but relatively thick, nearly high nodiform in profile (DPeI 188 - 196, LPeI 47 - 50); propodeal spines moderate (PSLI 20 - 21); postpetiole distinctly wider than petiole (PPI 119 - 129).

A member of the Afrotropical muralti species complex, which is part of the weitzeckeri species group.

Key to Tetramorium weitzeckeri-group species.

Distribution
This taxon was described from Democratic Republic of Congo.

Nomenclature

 *  akengense. Xiphomyrmex occidentalis subsp. akengensis Wheeler, W.M. 1922a: 194 (w.) DEMOCRATIC REPUBLIC OF CONGO. Junior synonym of occidentale: Bolton, 1980: 229. Revived from synonymy: Hita Garcia, Fischer & Peters, 2010b: 43. Raised to species: Hita Garcia, Fischer & Peters, 2010b: 43.

Hita Garcia et al. (2010) - Presently, T. akengense is only known from its type locality in the D.R. Congo. It was first described as variety of T. occidentale (Wheeler, W.M. 1922) and later synonymised under the latter (Bolton 1980). However, examination, and most importantly, measuring of all available material offered several arguments to raise T. akengense to species status. First, the shape of the petiolar node differs significantly between T. akengense and all the examined specimens of T. occidentale. The node is thickly squamiform in T. akengense, nearly high nodiform in lateral view (LPeI 47 - 50), and in dorsal view less than twice as wide as long (DPeI 188 - 196) while the node is squamiform in T. occidentale, in lateral view always 2.3 to 2.8 times higher than long (LPeI 36 - 43), and in dorsal view distinctly more than twice as wide as long (DPeI 225 - 268). Moreover, in T. akengense the postpetiole is distinctly wider than the petiolar node in dorsal view (PPI 119 - 129) whereas in T. occidentale the postpetiole is only slightly wider than the petiole (PPI 104 - 118). Additionally, the coloration of the examined T. akengense proved to be a reddish brown while all T. occidentale specimens showed a very dark brown, often black colour. Another morphologically close species is T. kakamega but it shows much larger propodeal spines (PSLI 27 - 28), a more transverse and higher petiolar node (DPeI 221 - 236, LPeI 39 - 43) and an impressed metanotal groove in profile. The presence of an impressed anterior clypeal margin distinguishes T. akengense from the remaining species of the muralti complex.

Worker
Hita Garcia et al. (2010) - HL 0.672 - 0.722 (0.702); HW 0.656 - 0.678 (0.662); SL 0.422 - 0.450 (0.437); EL 0.128 -0.150 (0.144); PW 0.483 - 0.506 (0.492); WL 0.756 - 0.800 (0.778); PSL 0.133 - 0.144 (0.142); PTL 0.128 - 0.139 (0.133); PTH 0.272 - 0.283 (0.277); PTW 0.250 - 0.261 (0.257); PPL 0.189 - 0.200 (0.193); PPH 0.267 - 0.278 (0.273); PPW 0.311 - 0.322 (0.316); CI 92 - 98 (94); SI 64 - 68 (66); OI 19 - 23 (22); PSLI 20 - 21 (20); PeNI 50 - 53 (52); LPeI 47 - 50 (48); DPeI 188 - 196 (193); PpNI 63 - 67 (64); LPpI 68 - 73 (71); DPpI 160 - 168 (164); PPI 119 - 129 (123) (9 measured).

Head longer than wide (CI 92 - 98). Anterior clypeal margin distinctly impressed medially. Frontal carinae strongly developed and sinuate, much weaker behind eye level, curving down ventrally between eye level and posterior margin of head to form the posterior and ventral margins of antennal scrobe. Scrobe well-developed and broad, with distinct margin all around. Antennal scape short (SI 64 - 68). Eyes small to moderate (OI 19 - 23), with 8 to 10 ommatidia in longest row. Metanotal groove in profile never impressed. Propodeal spines of medium size, triangular with a broad base (PSLI 20 - 21). Propodeal lobes small, triangular and acute. Petiolar node thickly squamiform, in dorsal view less than twice as wide as long (DPeI 188 - 196) and in lateral view mostly faintly above twice as high as long (LPeI 47 - 50), nearly high nodiform. Postpetiole rounded cuneiform, without sharp transverse dorsal margin, in dorsal view more than 1.6 times wider than long (DPpI 160 - 168) and much wider than petiole (PPI 119 - 129); in profile only weakly antero-posteriorly compressed, generally around 1.4 times higher than long (LPpI 68 - 73). Mandibles unsculptured, smooth and shiny. Clypeus with 3 distinct unbroken longitudinal rugae. Head mostly unsculptured, 1 strong median longitudinal ruga present between frontal carinae and 1 or 2 weaker developed rugulae between median ruga and frontal carinae, these often not reaching posterior eye level, antennal scrobe with median longitudinal ruga anteriorly not reaching posterior eye level. No cephalic ground sculpturation present. Dorsum of mesosoma generally unsculptured, sometimes very weak short longitudinal rugulation present on anterior pronotal dorsum. Petiole, postpetiole, and gaster completely unsculptured, smooth and shiny. All dorsal surfaces with numerous simple, fine, standing hairs. Fine pubescence on tibiae and antennal scapes appressed to decumbent. Colour uniformly reddish brown.

Type Material
Hita Garcia et al. (2010) - Xiphomyrmex occidentalis subsp. akengensis. Syntype workers, D.R. CONGO, Akengi, X.1913, leg. H.O Lang [examined]. Wheeler (1922) states in the original description that the type series was collected by Lang & Chapin, and Bolton (1980) provides the same collecting data. However, the labels of the syntypes in MCZ and of three specimens from the same series in BMNH show H.O. Lang as single collector and provide a collection date not given by Wheeler (1922) nor Bolton (1980).