Tetramorium mpala

Tetramorium mpala is currently only known from the type locality where it was collected in acacia woodland savannah at an elevation of 1650 m. The holotype was sampled on the ground, but until more material becomes available it remains unclear whether that is the primary stratum of T. mpala.

Identification
The character combination of very large eyes (OI 31) and first gastral tergite with long, fine decumbent to subdecumbent (rarely appressed) pilosity distinguishes T. mpala from the remainder of the T. weitzeckeri species complex.

The new species is readily distinguishable within the Tetramorium weitzeckeri species complex. The most obvious character is certainly the pilosity on the first gastral tergite, which is long, fine and subdecumbent to decumbent in T. mpala., whereas the remainder of the complex either lacks any long pilosity at all (Tetramorium bendai, Tetramorium humbloti, Tetramorium sepultum and Tetramorium tanaense) or possesses long, suberect to erect pilosity (Tetramorium boltoni, Tetramorium guineense, Tetramorium renae, Tetramorium snellingi and Tetramorium weitzeckeri). The second-best character is eye size, since T. mpala has the largest eyes (OI 31) encountered in the species complex, which contrast with the generally much smaller eyes of the other species (usually OI 16–26, only a few specimens of T. humbloti and all of T. tanaense have OI 27–29).

Another aspect that deserves attention here is the shape of the petiolar node in T. mpala. It is clearly squamiform like in all species of the T. weitzeckeri complex, but also similar to the high cuneiform and slightly triangular form found in some species of the Afrotropical T. squaminode species group (Bolton 1980) or the Malagasy T. marginatum and T. bonibony species groups (Hita Garcia & Fisher 2012a).

Distribution based on Regional Taxon Lists
Afrotropical Region: Kenya.

Castes
Known only from the worker caste.

Nomenclature

 *  mpala. Tetramorium mpala Hita Garcia & Fischer, 2014: 11, figs. 3C, 6A, D, 11, 12 (w.) KENYA.

Worker
(N=1) Measurements: HL 0.79; HW 0.74; SL 0.60; EL 0.23; PH 0.44; PW 0.59; WL 1.04; PSL 0.28; PTL 0.12; PTH 0.36; PTW 0.35; PPL 0.26; PPH 0.38; PPW 0.42; CI 94; SI 71; OI 31; DMI 57; LMI 42; PSLI 35; PeNI 59; LPeI 33; DPeI 292; PpNI 71; LPpI 68; DPpI 162; PPI 120. Head longer than wide (CI 94); posterior head margin in full-face view flat to weakly concave; anterior clypeal margin with distinct median impression; frontal carinae strongly developed, distinctly raised, and very long, approaching or ending at posterior head margin; antennal scrobes present, but shallow and without clearly defined posterior and ventral margins. Antennal scapes of moderate length, not reaching posterior head margin (SI 81). Eyes very large (OI 31).

Mesosomal outline in profile weakly to moderately convex, moderately marginate from lateral to dorsal mesosoma, comparatively high and stout (LMI 42); promesonotal suture present, weak but clearly visible; metanotal groove well developed and in profile moderately deep. Propodeal spines long, spinose and acute (PSLI 35); propodeal lobes short, triangular and blunt. Petiolar node squamiform to thinly high cuneiform and slightly triangular, in profile three times higher than long (LPeI 33), anterodorsal and posterodorsal margins relatively rounded and posterodorsal margin less well developed than anterodorsal, petiolar dorsum tapering backwards; node in dorsal view of strongly transverse elliptical shape, around 2.9 times as wide as long (DPeI 292). Postpetiole in profile subglobular to weakly anteroposteriorly compressed, approximately 1.5 times as high as long (LPpI 68); in dorsal view around 1.6 times as wide as long (DPpI 162). Postpetiole in profile appearing higher and more voluminous than petiolar node, in dorsal view 1.2 times as wide as petiolar node (PPI 120).

Mandibles striate; clypeus longitudinally rugulose with six more or less irregular rugulae, median rugula not well developed; cephalic dorsum between frontal carinae irregularly longitudinally rugose with around eight rugae, rugae running from posterior clypeal margin to posterior head margin, but some broken, meandering or with cross-meshes; scrobal area partly unsculptured, but mostly merging with surrounding reticulate-rugose to longitudinally rugose sculpture present on lateral and ventral. Mesosoma laterally and dorsally longitudinally rugose, laterally slightly more irregularly so. Forecoxae unsculptured, smooth and shining. Both waist segments and gaster completely unsculptured, smooth and shining. Ground sculpture generally faint to absent everywhere on body. Head with moderately abundant standing pilosity; mesosoma with six pairs of long, fine, standing hairs; petiole with three pairs of long, fine, standing hairs and postpetiole with four pairs of subdecumbent to decumbent, long, fine hairs; first gastral tergite with fairly long, fine and subdecumbent to decumbent pilosity. Anterior edges of antennal scapes and metatibiae with appressed hairs. Body colouration chestnut brown to dark brown, appendages lighter in colour and gaster much darker than remainder of body.

Type Material
Holotype. KENYA: Pinned worker, Rift Valley Province, Laikipia District, Mpala Research Centre, 0.29° S, 36.9° E, 1650 m, Acacia woodland, foraging on ground, collection code RRS01-188, 2 Apr. 2001, R.R. Snelling, unique specimen identifier CASENT0247445.

Etymology
The name of the new species is inspired by the type locality, the Mpala Research Centre, which is an important research facility in Kenya. The species epithet is a nominative noun in apposition and thus invariant.

References based on Global Ant Biodiversity Informatics

 * Hita Garcia F., and G. Fischer. 2014. Additions to the taxonomy of the Afrotropical Tetramorium weitzeckeri species complex (Hymenoptera, Formicidae, Myrmicinae), with the description of a new species from Kenya. European Journal of Taxonomy 90: 116.