The ant genus Tetramorium Mayr in the Afrotropical region (Hymenoptera, Formicidae, Myrmicinae): synonymisation of Decamorium Forel under Tetramorium, and taxonomic revision of the T. decem species group

Abstract In this study we synonymise the genus Decamorium Forel under Tetramorium Mayr, revise the new T. decem species group by providing a diagnosis of the group, an illustrated identification key to species level, and worker-based species descriptions for all five species, which include diagnoses, discussions, images, and distribution maps. The following species are revised in this study: T. decem Forel, comb. r., T. raptor sp. n., T. uelense Santschi, comb. r., T. ultor Forel, comb. r., stat. r. & stat. n., and T. venator sp. n. In addition, we also designate lectotypes for T. decem, T. uelense, and T. ultor.


Introduction
The genus Tetramorium Mayr is globally distributed and with 520 valid species it represents one of the most species-rich ant genera (Bolton 2014). The vast majority of these are found in the tropics of the Old World. In the Afrotropical and Malagasy regions, Tetramorium is hyperdiverse by the definitions of Wilson (2003) and Moreau (2008). In Madagascar and the neighbouring islands of the Indian Ocean, recent studies have revealed a highly endemic and astonishingly diverse Tetramorium fauna consisting of around 120 species (Bolton 1979;Hita Garcia and Fisher 2011, 2012a, 2012b. The known Afrotropical Tetramorium fauna was thoroughly revised by Bolton (1976Bolton ( , 1980Bolton ( , 1985, parts of which were recently updated by Hita Garcia et al. (2010) and Hita Fisher (2011, 2013), producing a current total of 224 species. In addition, there are at least 100 more undescribed Afrotropical species located in several museum collections awaiting formal description (FHG, unpublished data). Traditionally, what is now considered as Tetramorium was divided into the genera Atopula Emery, Macromischoides Wheeler, Tetramorium, and Xiphomyrmex Forel until Bolton's genus-level revision (1976). The name Tetramorium was used for a much smaller subset of species with twelve antennal segments. Bolton provided ample evidence for the artificiality of these genera and synonymised them under Tetramorium. Particularly noteworthy is the fact that the previous separation of Xiphomyrmex (11-segmented antennae) from Tetramorium (12-segmented antennae) was based solely on the difference in the antennomere count; Bolton showed this character to be variable in other tetramoriine genera. Forel (1913a) described Decamorium Forel as a subgenus of Tetramorium on the basis of the ten-segmented antennae and the very pronounced and deep antennal scrobes. A few years later Arnold (1917) followed Forel and also treated Decamorium as a subgenus of Tetramorium. He based his decision on the ten-segmented antennae, the well-defined and deep antennal scrobes, the obsolete lateral ridges of the clypeus, and the strongly swollen tibiae and femorae in the worker caste. Nevertheless, apart from these two works (Forel 1913a;Arnold 1917), most other authors (and later even Forel himself) have treated Decamorium as a genus distinct from Tetramorium (Emery 1914(Emery , 1924Forel 1917;Wheeler 1922;Bernard 1953;Bolton 1973Bolton , 1976Bolton , 1995. In his classification of the Myrmicinae, Emery (1914) was the first to treat Decamorium as a "genus" rather than a subgenus, although he did not provide any explanation of his decision. Later, in his "Genera Insectorum", Emery (1924) continued to list Decamorium as a genus. In that work he re-described the genus and separated it from the other then known tetramoriine genera, again on the basis of the ten-segmented antennae of the workers and queens. All subsequent authors listed Decamorium as a genus without taxonomic treatment until Bolton's (1976) revision of the tribe Tetramoriini. As mentioned above, he diagnosed most of the currently valid genera of the tribe and also reviewed Decamorium. Bolton (1976) clearly stated that the separation of Decamorium from Tetramorium on the grounds of the reduced antennal count, reduced clypeal shield, and differences in mandibular dentition was relatively dubious. He doubted that these characters would persist to diagnose Decamorium in the future. However, since then nothing more on the generic limits or alpha taxonomy of Decamorium has been published, and all authors continued to list Decamorium as a distinct genus (e.g. Hölldobler and Wilson 1990;Bolton 1995Bolton , 2003Bolton , 2014Robertson 2000;.
In this study we propose Decamorium as a junior synonym of Tetramorium and lower it to the arbitrary rank of a species group. Our decision is based on a critical analysis of the diagnostic characters previously defining Decamorium. In addition, we revise the alpha taxonomy of the T. decem species group. A diagnosis of the T. decem species group is given together with an illustrated identification key to species on the basis of the worker caste. In addition, all members of the species group are described/ re-described including diagnoses, discussions, high-quality montage images and distribution maps.

Abbreviations of depositories
The collection abbreviations follow Evenhuis (2014). The material upon which this study is based is located and/or was examined at the following institutions: essarily match the number of listed specimen-level codes because pins can sometimes hold more than one specimen, especially for older species. Digital colour montage images were created using a JVC KY-F75 digital camera and Syncroscopy Auto-Montage software (version 5.0), or a Leica DFC 425 camera in combination with the Leica Application Suite software (version 3.8). All images presented are available online and can be seen on AntWeb (http://www.antweb.org). The distribution maps we provide  were generated with the R software (R Core Team 2014). We measured 83 workers with a Leica MZ 12.5 equipped with an orthogonal pair of micrometers at a magnification of 100×. Measurements and indices are presented as minimum and maximum values with arithmetic means in parentheses. In addition, all measurements are expressed in mm to two decimal places. The following measurementsand indices used in this study follow Hita Garcia and Fisher (2011, 2012a, 2012b, 2013:

HL
Head length: maximum distance from the midpoint of the anterior clypeal margin to the midpoint of the posterior margin of head, measured in full-face view. Impressions on the anterior clypeal margin and the posterior head margin reduce head length. HW Head width: width of the head directly behind the eyes measured in full-face view.

SL
Scape length: maximum scape length excluding basal condyle and neck.

EL
Eye length: maximum diameter of compound eye measured in oblique lateral view.

PW
Pronotal width: maximum width of the pronotum measured in dorsal view.

WL
Weber's length: diagonal length of the mesosoma in lateral view from the posteroventral margin of propodeal lobe to the anterior-most point of pronotal slope, excluding the neck. PSL Propodeal spine length: the tip of the measured spine, its base, and the centre of the propodeal concavity between the spines must all be in focus. Using a dual-axis micrometer the spine length is measured from the tip of the spine to a virtual point at its base where the spine axis meets orthogonally with a line leading to the median point of the concavity. PTH Petiolar node height: maximum height of the petiolar node measured in lateral view from the highest (median) point of the node to the ventral outline. The measuring line is placed at an orthogonal angle to the ventral outline of the node. PTL Petiolar node length: maximum length of the dorsal face of the petiolar node from the anterodorsal to the posterodorsal angle, measured in dorsal view excluding the peduncle. PTW Petiolar node width: maximum width of the dorsal face of the petiolar node measured in dorsal view. PPH Postpetiole height: maximum height of the postpetiole measured in lateral view from the highest (median) point of the node to the ventral outline. The measuring line is placed at an orthogonal angle to the ventral outline of the node. PPL Postpetiole length: maximum length of the postpetiole measured in dorsal view. PPW Postpetiole width: maximum width of the postpetiole measured in dorsal view.

OI
Ocular index: EL / HW * 100 Pubescence and pilosity are often of high diagnostic value within the genus Tetramorium (e.g. Bolton 1976Bolton , 1980Bolton , 1985Hita Garcia et al. 2010;Fisher 2012a, 2012b). The varying degree of inclination of pilosity is particularly important for the diagnosis of groups or species. In this context we use the terms "erect", "suberect", "subdecumbent", "decumbent", and "appressed" following Wilson (1955). The terminology used for the description of surface sculpturing follows Harris (1979) and Bolton (1980). Proposed without designation of type species and therefore unavailable. Species included by Kratochvíl (1941)

Antennomere count
As outlined above, the antennomere count was the main diagnostic character qualifying Decamorium as a genus (Emery 1924;Bolton 1976). Antennomere count has traditionally been considered a very good diagnostic character for separating closely related genera. Yet over the past few decades it has become apparent that the antennal count can vary within a genus, sometimes significantly. Some examples include the genera Carebara Westwood with eight to eleven segments (Fernandez 2004), Temnothorax Mayr which typically has twelve segments, rarely eleven (Bolton 2003;Radchenko 2004), Cardiocondyla Emery with eleven and twelve segments (Seifert 2003), or Pheidole with nine to twelve (Bolton 2003). Also, in some African species of Carebara the major workers always have one antennal segment more than the minor workers. Furthermore, subgroups of the same genus often have been placed in different genera in the past due to varying antennomere counts. One good example is Myrmelachista Roger outlined in Longino (2006). It was originally described by Roger (1863) as two genera: Decamera Roger (a junior homonym of a beetle genus and replaced by the name Hincksidris Donisthorpe) having ten-segmented antennae, and Myrmelachista having eleven-segmented antennae. This division turned out to be incorrect, and Brown (1973) and Snelling and Hunt (1976) formally synonymised them more than a century later.
In what is now considered to be Tetramorium one can find eleven-segmented and twelve-segmented antennae throughout all biogeographical regions, even though most of these forms were previously separated into Xiphomyrmex (11-segmented antennae) and Tetramorium (12-segmented antennae). Bolton (1976) provided evidence based on sting appendage types showing that this separation was an artificial one, and consequently synonymised Xiphomyrmex under Tetramorium. Based on this intrageneric variation in antennal segmentation, we accept that a small and highly specialised African species group within Tetramorium could have an even more reduced count of ten antennal segments. This is further supported by the presence of a very small species from India that possesses 10-segmented antennae: T. decamerum (Forel). This species was treated as Triglyphothrix by Bolton (1976), thus not taken into consideration as a Tetramorium. The later synonymisation of Triglyphothrix under Tetramorium Bolton (1985) provided a "genuine" Tetramorium with 10-segmented antennae. Consequently, this character is not unique to Decamorium, but already present in Tetramorium.

Clypeal shield
The reduced clypeal shield seen in Decamorium (Fig. 1A) is not unique to its species. Within the tropical Tetramorium fauna most species have a very well-developed and clearly distinctive clypeal shield (Figs 1F, 1G, 1F, 1I), but there are a number of species, such as T. nodiferum (Emery) (Fig. 1B), T. simulator Arnold (Fig. 1C), T. aculeatum (Mayr) (Fig. 1D), or T. anodontion Bolton (Fig. 1E), in which this shield is much less pronounced or almost reduced. The clypeal shield generally varies from species to species in its height and the sharpness of its dorsal edge. When the development of this character across several hundred Tetramorium species is considered, Decamorium emerges as one extreme of a cline that ranges from almost no clypeal shield to a very sharp and high shield, such as in the members of the T. sericeiventre Emery species group (Fig. 1I).

Mandibular dentition
The mandibular dentition of Decamorium and Tetramorium seemed slightly different back in 1976, but as anticipated by Bolton, it has become clear that there is much more variation within Tetramorium. Currently there is no significant difference in mandibular dentition between Decamorium and Tetramorium. In Decamorium the mandibular count consists of three apical teeth followed by a series of four or five denticles, while in Tetramorium there are two to three apical teeth followed by a series of three to eight denticles (Bolton 2003). Consequently, this character has no diagnostic importance in this group since the values of Decamorium fall well within the range of the larger Tetramorium.

Tetramorium simulator Arnold
If one considers the whole tribe Tetramoriini, then it becomes apparent that the specialised habitus of Decamorium is not unique. Several authors have stated that Decamorium are specialised termite hunters, and that their specialised morphology could be an adaptation to such a dangerous lifestyle (Arnold 1917;Bolton 1976;Longhurst et al. 1979). Interestingly, both Arnold (1917) in the original description and later Bolton (1980) noted the similarities in general body shape and diet between members of Decamorium and the species Tetramorium simulator from South Africa. We agree that the similarities in morphology are indeed obvious, especially in profile view (Fig. 2). However, at present it is not clear whether the shared morphology is based on a close phylogenetic relationship between Decamorium and T. simulator or a result of convergent evolution due to a similar lifestyle hunting termites. We believe the latter more likely since the twelve-segmented antennae, the much broader head, and sculptured clypeus of T. simulator suggest a closer relationship to another group with twelve-segmented antennae than to Decamorium. Therefore, we hypothesise that both have evolved from different Tetramorium lineages and acquired the specialised habitus independently from each other. Another remarkable aspect is the lack of a strong and sharp clypeal shield in T. simulator, which seems to have been reduced in a manner almost similar, though less pronounced, to Decamorium.

Male morphology
We do not intend to go into details of male morphology here, but so far there is not a single character that would separate the males of Decamorium from the males of Tetramorium; a result that agrees with Bolton's findings (1976). It should be noted, however, that Decamorium males are very rare, and only one specimen was available for examination (BMNH: CASENT0901037).

Molecular evidence
In addition to our morphological analysis above, there is also molecular evidence supporting the synonymisation of Decamorium under Tetramorium. Based on a multigene dataset, Ward et al. (in press) show that Decamorium is nested within a larger Tetramorium clade. However, how Decamorium is integrated into Tetramorium and to which groups/lineages it is most closely related remains unknown. Further phylogenetic/phylogenomic studies that deal with a greater number of species groups and a good proportion of species are needed to clarify relationships within the hyperdiverse Tetramorium and its satellite genera.

Diagnosis of Tetramorium decem species group
Ten-segmented antennae; antennal scape relatively short (SI 67-76); anterior clypeal margin with distinct but often shallow impression; frontal carinae strongly developed and noticeably raised, forming dorsal margin of very well-developed antennal scrobes, curving down ventrally and anteriorly halfway between posterior eye margin and posterior head margin and forming posterior and usually ventral scrobe margins; antennal scrobes very well developed, deep and usually with clearly defined margins all around, median scrobal carina absent; eyes relatively large (OI 32-40); mesosoma relatively flat, low, and elongated, margination between lateral and dorsal mesosoma moderately developed (LMI 33-38); propodeum armed with short triangular to elongate-triangular teeth (PSLI 9-19); propodeal lobes short, rounded to triangular; tibiae and femorae strongly swollen; petiolar node nodiform with moderately rounded antero-and posterodorsal margins, petiolar dorsum weakly to strongly convex, node in profile between 1.0 to 1.3 times higher than long (LPeI 77-100), node in dorsal view around 1.1 to 1.3 times longer than wide (DPeI 76-92); postpetiole in profile globular, around 1.1 to 1.4 times higher than long (LPpI 71-88); mandibles and clypeus unsculptured, smooth, and shiny; sculpture on cephalic dorsum between frontal carinae and dorsal mesosoma variable, ranging from unsculptured, smooth, and shiny to longitudinally rugose/rugulose, often punctate or puncticulate; petiole usually weakly sculptured, postpetiole unsculptured to weakly sculptured; gaster unsculptured, smooth, and shiny; pilosity greatly reduced, head with several pairs of standing hairs, mesosoma with one pair, waist segments sometimes with one long pair each, and sometimes first gastral tergite with one pair; sting appendage triangular.

Taxonomic and biogeographic notes on the group
The T. decem species group is endemic to the Afrotropical region where it is widely distributed ( Fig. 3). Tetramorium raptor and T. uelense are found in West and Central Africa and T. venator occurs through most of the equatorial rainforest belt from Liberia in West Africa to Western Kenya. By contrast, T. decem and T. ultor are species from eastern and southeastern Africa. Surprisingly, the group seems to be absent from South Africa based on the material available to us, but T. decem or T. ultor are likely to be found there or in neighbouring Botswana or Namibia. Furthermore, we expect the distribution ranges of T. decem, T. uelense, and perhaps T. ultor to expand with further ant inventory or collecting projects in Afrotropical savannahs, dry forests, and other arid habitats. These were sparsely sampled in sub-Saharan Africa in the past since most modern ant inventories have focused on rainforests (e.g. Belshaw and Bolton 1994;Watt et al. 2002;Fisher 2004;Yanoviak et al. 2007;Hita Garcia et al. 2009), whereas only a few studies have examined ant faunas from drier localities (e.g. Robertson 1999Robertson , 2002Braet and Taylor 2008).
The separation of the T. decem species group from all other Tetramorium species groups is straightforward and easy. So far, only the members of the T. decem group have ten-segmented antennae, whereas all other Afrotropical Tetramorium have either eleven or twelve. Consequently, the T. decem species group is unlikely to be confused with another Afrotropical group. The morphology of the five species of the group is very uniform, likely due to their strongly specialised lifestyle, which makes the taxonomy of the group challenging at first sight. However, good diagnostic characters separate them fairly well from each other, especially eye size, propodeal spine/teeth length, petiolar node shape, mesosomal sculpture, and body colouration. These characters are remarkably consistent within each species throughout its whole distribution, as are the species-specific habitat preferences.

Identification key for T. decem species group (workers)
1 Dorsum of promesonotum with conspicuous longitudinally rugose/rugulose sculpture (Fig. 4A 2 Slightly smaller species (WL 0.88-0.93); propodeum armed with shorter, triangular, and acute teeth (PSLI 10-11); dorsum of promesonotum longitudinally rugulose with very little ground sculpture, lateral pronotum mostly unsculptured and shiny, only dorsally longitudinally rugulose; generally of uniform dark brown colour; rainforest species ( Fig. 5A Generally smaller species (WL 0.85-0.98); propodeal teeth relatively shorter (PSLI 9-13); petiolar node relatively lower, in profile around 1.0 to 1.2 times higher than long (LPeI 86-100); usually of uniform brown colour, if bicoloured, then only slightly so and never as well developed as above (Fig. 6B)  [Note: the GPS data of the type locality was not provided by the locality label or the original description. The data presented above is based on our own geo-referencing   Diagnosis. Tetramorium decem can be recognised by the following combination of characters: relatively larger species (HW 0.59-0.62; WL 1.02-1.16); propodeal teeth relatively longer ; petiolar node in profile around 1.2 to 1.3 times higher than long (LPeI 77-82); dorsum of promesonotum unsculptured, smooth, and very shiny; strongly bicoloured species with dark brown or black gaster contrasting with light brown to reddish brown remainder of body.  Worker description. Head much longer than wide (CI 83-85); posterior head margin weakly concave. Anterior clypeal margin with distinct, but often shallow median impression. Frontal carinae strongly developed and noticeably raised forming dorsal margin of very well-developed antennal scrobes, curving down ventrally and anteriorly halfway between posterior eye margin and posterior head margin and forming posterior and parts of ventral scrobe margins; antennal scrobes very well developed, deep and with clearly defined margins, but ventral margin less strongly developed, median scrobal carina absent. Antennal scapes short, not reaching posterior head margin (SI 70-76). Eyes very large (OI 32-34). Mesosomal outline in profile flat to weakly convex, relatively low and elongate (LMI 32-34), moderately to strongly marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove present, distinct, and clearly impressed. Propodeal spines short, elongate-triangular, and moderately acute , propodeal lobes short, triangular, and usually blunt, always significantly shorter than propodeal spines. Tibiae and femorae strongly swollen. Petiolar node nodiform with moderately rounded antero-and posterodorsal margins, around 1.2 to 1.3 times higher than long (LPeI 77-82), anterior and posterior faces approximately parallel, anterodorsal and posterodorsal margins situated at about the same height, petiolar dorsum clearly convex; node in dorsal view between 1.1 to 1.2 times longer than wide (DPeI 85-92), in dorsal view pronotum around 2.0 to 2.2 times wider than petiolar node (PeNI 46-51). Postpetiole in profile globular to subglobular, approximately 1.3 to 1.4 times higher than long (LPpI 71-77); in dorsal view around 1.3 to 1.4 times wider than long (DPpI 128-138), pronotum between 1.3 to 1.5 times wider than postpetiole (PpNI 67-76). Postpetiole in profile usually appearing less voluminous than petiolar node, postpetiole in dorsal view around 1.4 to 1.5 times wider than petiolar node (PPI 143-149). Mandibles and clypeus usually fully unsculptured, smooth, and shining, mandibles sometimes with few traces of rugulae apically; cephalic dorsum between frontal carinae mostly unsculptured and shiny, median ruga present and distinct, cephalic dorsum also puncticulate to punctate throughout its length, posteriorly close to posterior head margin especially pronounced; scrobal area partly unsculptured, smooth and shiny and partly merging with surrounding rugose sculpture on sides of head. Ground sculpture on head usually weak to absent. Dorsum of mesosoma mostly unsculptured, smooth and shiny with scattered punctures, rarely with few traces of rugulae; lateral mesosoma longitudinally rugose and very conspicuously reticulate-punctate except for mostly unsculptured lateral pronotum and katepisternum. Forecoxae unsculptured, smooth, and shining. Petiolar node and postpetiole superficially longitudinally rugulose or irregularly rugulose superimposed on conspicuous but relatively weak reticulate-punctate ground sculpture. Mesosoma and waist segments appearing mostly matt. First gastral tergite unsculptured, smooth, and shiny. Pilosity and pubescence greatly reduced: head with few pairs of moderately long, standing hairs, anterior pronotum with one long pair, waist segments sometimes with one long pair each, and sometimes first gastral tergite with one long pair; appressed pubescence present everywhere on body, but noticeable only on antennae, cephalic dorsum, legs, and first gastral tergite. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with appressed hairs. Body strongly bicoloured with dark brown to black gaster contrasting with light brown to reddish brown remainder.
Distribution and biology. The distribution range of T. decem is far smaller than previously thought (Fig. 3). Indeed, most of the material listed in the literature as T. decem or labelled as such in museum collections turned out to be either T. ultor or T. venator, while only a few collections proved to be genuine T. decem. Based on the redefined species definition, T. decem is only known from the type locality in Zimbabwe and two additional localities in East Africa: Arabuko Sokoke in Kenya and Mkomazi in Tanzania. Nevertheless, if more extensive sampling efforts are undertaken in East Africa, T. decem is likely to be found in more localities in Kenya, Tanzania, and Zimbabwe. Like T. uelense and T. ultor, T. decem prefers arid habitats, such as savannah and woodland. Based on Arnold (1917) and the collection label from some material from Arabuko Sokoke, T. decem nests in sandy soil. The diet consists of termites, as with most other members of the species group.
Discussion. Tetramorium decem is the core species of the group, and was the type species for the description of the subgenus Decamorium by Forel (1913a). It is perhaps the most conspicuous species of the group. Its bicolouration, larger size, lack of sculpture on the mesosomal dorsum, and a higher petiolar node render it immediately recognisable. The mostly unsculptured, smooth and shiny mesosomal dorsum distinguishes T. decem from T. raptor and T. uelense, in which the dorsum of the mesosoma is clearly longitudinally rugose/rugulose. Tetramorium ultor and T. venator both share the lack of sculpture on the mesosomal dorsum with T. decem, but can still be easily separated from the latter. Tetramorium decem is generally larger in size (WL 1.02-1.16), has longer propodeal spines  and is also conspicuously bicoloured, whereas T. ultor and T. venator are smaller species (WL 0.85-0.98) with significantly shorter propodeal teeth (PSLI 9-13) and a more uniform brown to black body colouration. In addition, T. decem also has a higher petiolar node, in profile around 1.2 to 1.3 times higher than long (LPeI 77-82), compared to the other two, in which the node in profile is only around 1.0 to 1.2 times higher than long (LPeI 86-100). The species that appears to be morphologically closest to T. decem is T. uelense. Both species share the large body, bicolouration, and preference for arid habitats. However, in addition to the sculpture on the mesosoma, T. uelense also has a lower petiolar node, in profile around 1.1 times higher than long (LPeI 88-93). Another character that is shared between T. decem and T. uelense but absent in the other species of the group is the development of the ventral margin of the antennal scrobe. In T. raptor, T. ultor, and T. venator the margin is clearly and well defined, while in T. decem and T. uelense it is less so and merges more with the surrounding rugose sculpture.
Variation. Based on the available material we did not observe any significant form of intraspecific variation in T. decem. [Note: the GPS data of the type locality was not provided by the locality label. The data presented above is based on our own geo-referencing of the Bakundu Forest located in the province Sud-Ouest. Consequently, it should be considered an approximation and not the exact position of the type locality. Diagnosis. Tetramorium raptor is easily recognisable within the group on the basis of the following combination of characters: relatively smaller species (WL 0.88-0.93); very large eyes (OI 35); propodeum armed with very short triangular teeth (PSLI 10-11); petiolar node in profile around 1.1 times higher than long (LPeI 89-93); dorsum of mesosoma with longitudinally rugulose sculpture; body uniformly dark brown, appendages of lighter brown. Worker description. Head much longer than wide (CI 80-83); posterior head margin weakly concave. Anterior clypeal margin with distinct but often shallow median impression. Frontal carinae strongly developed and noticeably raised forming dorsal margin of very well-developed antennal scrobes, curving down ventrally and anteriorly halfway between posterior eye margin and posterior head margin and forming posterior and ventral scrobe margins; antennal scrobes very well developed, deep and with clearly defined margins all around, median scrobal carina absent. Antennal scapes short, far from reaching posterior head margin (SI 70-73). Eyes relatively large (OI 35). Mesosomal outline in profile relatively flat, elongate and low (LMI 35-37), moderately to strongly marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove present and conspicuous, but relatively shallow. Propodeum armed with short, triangular, and usually acute teeth (PSLI 10-11), propodeal lobes short, well round-ed, and usually larger than propodeal teeth. Petiolar node nodiform with moderately rounded antero-and posterodorsal margins, in profile around 1.1 times higher than long (LPeI 89-93), anterior and posterior faces approximately parallel, anterodorsal and posterodorsal margins situated at about same height and equally angled, petiolar dorsum weakly convex; node in dorsal view around 1.2 to 1.3 times longer than wide (DPeI 80-85), in dorsal view pronotum around 2.0 to 2.2 times wider than petiolar node (PeNI 47-51). Postpetiole in profile globular, approximately 1.1 to 1.2 times higher than long (LPpI 81-88); in dorsal view around 1.2 and 1.3 times wider than long (DPpI 123-130), pronotum around 1.4 to 1.6 times wider than postpetiole (PpNI 64-70). Postpetiole in profile appearing less voluminous than petiolar node, postpetiole in dorsal view around 1.4 to 1.5 times wider than petiolar node (PPI 137-150). Mandibles and clypeus unsculptured, smooth, and shining; cephalic dorsum between frontal carinae with fine irregularly longitudinally rugulose sculpture, rugulae running from posterior clypeal margin to posterior head margin, often interrupted or meandering, rarely with cross-meshes, cephalic dorsum also puncticulate to punctate throughout its length, otherwise without ground sculptured; scrobal area partly unsculptured, smooth and shiny and partly strongly reticulate-punctate; lateral head mainly reticulate-rugose with weak to moderately well developed punctate ground sculpture. Dorsum of mesosoma densely longitudinally rugulose, anteriorly without much ground sculpture, posteriorly on top of strong reticulate-punctate ground sculpture; lateral pronotum and katepisternum mostly unsculptured, smooth, and shiny, remainder of lateral mesosoma irregularly rugose and very conspicuously reticulate-punctate. Forecoxae unsculptured, smooth, and shining. Petiolar node laterally reticulate-punctate, dorsum of node mostly unsculptured, smooth, and shiny; postpetiole mostly unsculptured, smooth, and shiny with scattered punctures. First gastral tergite unsculptured, smooth, and shiny. Pilosity and pubescence greatly reduced: head with few pairs of moderately long, standing hairs, anterior pronotum with one long pair, waist segments sometimes with one long pair each, and sometimes first gastral tergite with one long pair; appressed pubescence present everywhere on body, but noticeable only on antennae, cephalic dorsum, legs, and first gastral tergite. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with appressed hairs. Body uniformly dark brown to black, appendages of lighter brown.
Etymology. The name of the new species is Latin and means "thief, robber, or plunderer". It refers to the predaceous lifestyle of T. raptor. The species epithet is a nominative noun, and thus invariant.
Distribution and biology. Tetramorium raptor is currently only known from the type locality Bakundu in the southeast of Cameroon and from Gambari in southwestern Nigeria (Fig. 3). Based on the minimal collection label data, T. raptor lives in rainforest leaf litter.
Discussion. Tetramorium raptor is an easily distinguishable member of the T. decem group, but was not recognised until this study. Indeed, all known material was collected in 1969 and 1990, but labelled as T. uelense on the basis of the distinctive sculpture on the mesosomal dorsum. The presence of conspicuous, longitudinally rugulose sculpture on the dorsum of the promesonotum distinguishes it from T. decem, T. ultor, or T. venator, since the latter three all lack sculpture on the promesonotal dorsum. Tetramorium uelense, however, shares the presence of sculpture on the mesosomal dorsum with T. raptor, which led to the abovementioned misidentifications. Nevertheless, careful examination of all material previously listed as T. uelense revealed the presence of two morphologically and ecologically different species. The most obvious differences are body size and colour. Tetramorium uelense is strongly bicoloured and larger (WL 0.98-1.06) than the smaller and uniformly-coloured T. raptor . The latter also has shorter propodeal teeth (PSLI 10-11) than T. uelense . Furthermore, T. raptor possesses a longitudinally rugulose promesonotal dorsum with very little ground sculpture and a mostly unsculptured and shiny lateral pronotum, whereas T. uelense has a promesonotal dorsum that is longitudinally rugose with distinct punctate ground sculpture and a lateral pronotum that is conspicuously rugose with prominent ground sculpture. In addition, both species also differ in habitat choice, as Tetramorium uelense seems to prefer savannah while T. raptor lives in rainforest.
Variation. Based on material from the two known localities, there is no intraspecific variation in T. raptor. Santschi, 1923, comb. r. Figs 3, 4B, 5C, 5D, 10 Tetramorium (Decamorium) decem uelense Santschi, 1923: 285. [Combination in Decamorium and raised to species by Bolton 1976: 298.] Decamorium decem nimba Bernard, 1953: 250 [Note: GPS data for neither of the type localities was included on the locality labels or the original descriptions. The data presented above is based on our own georeferencing of Vankerhovenville located in Province Orientale and Kéoulenta located in the Nzérékoré Region. Consequently, they should be considered approximations and not the exact positions of the type localities.]
Diagnosis. The following character combination separates T. uelense from the other species of the T. decem species group: relatively larger species (WL 0.98-1.06); propodeum armed with short triangular to elongate-triangular teeth (PSLI 16-18); petiolar node in profile around 1.1 times higher than long (LPeI 88-93); dorsum of mesosoma conspicuously longitudinally rugose with distinctive reticulate-punctate ground sculpture; strongly bicoloured with dark brown to black gaster contrasting with light brown to reddish brown remainder of body. Worker description. Head much longer than wide (CI 80-83); posterior head margin weakly concave. Anterior clypeal margin with distinct, but often shallow median impression. Frontal carinae strongly developed and noticeably raised forming dorsal margin of very well-developed antennal scrobes, curving down ventrally and anteriorly halfway between posterior eye margin and posterior head margin and forming posterior and ventral scrobe margins; antennal scrobes very well developed, deep and with clearly defined margins, but ventral margin less strongly developed, median scrobal carina absent. Antennal scapes short, far from reaching posterior head margin (SI 69-74). Eyes relatively large . Mesosomal outline in profile relatively flat, elongate and low (LMI 35-37), moderately to strongly marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove present, distinct, but relatively shallow. Propodeum armed with short, triangular to elongate-triangular, and acute teeth (PSLI 16-18), propodeal lobes reduced, short, and well rounded, usually shorter than propodeal teeth. Tibiae and femorae strongly swollen. Petiolar node nodiform with moderately rounded antero-and posterodorsal margins, in profile around 1.1 times higher than long (LPeI 88-93), anterior and posterior faces approximately parallel, anterodorsal and posterodorsal margins situated at about same height and equally angled, petiolar dorsum clearly convex; node in dorsal view around 1.2 to 1.3 times longer than wide (DPeI 77-81), in dorsal view pronotum between 2.0 and 2.1 times wider than petiolar node (PeNI 48-49). Postpetiole in profile globular, approximately 1.2 to 1.3 times higher than long (LPpI 75-86); in dorsal view between 1.2 and 1.3 times wider than long (DPpI 122-125), pronotum around 1.4 times wider than postpetiole (PpNI 69-70). Postpetiole in profile more or less of same volume as petiolar node, postpetiole in dorsal view around 1.4 times wider than petiolar node (PPI 141-145). Mandibles and clypeus unsculptured, smooth, and shining; cephalic dorsum between frontal carinae with fine irregularly longitudinally rugulose/ rugose sculpture, rugulae/rugae often interrupted, meandering, or with cross-meshes, cephalic dorsum also puncticulate to punctate throughout its length; scrobal area strongly reticulate-punctate; lateral head mainly reticulate-rugose with weak to moderately well developed punctate ground sculpture. Ground sculpture on head usually weak, except scrobal area (see above). Dorsum of mesosoma densely longitudinally rugose on top of strong punctate ground sculpture; lateral mesosoma longitudinally rugose and very conspicuously reticulate-punctate. Forecoxae unsculptured, smooth, and shining. Petiolar node and postpetiole superficially longitudinally rugulose or irregularly rugulose superimposed on conspicuous but relatively weak reticulate-punctate ground sculpture. Mesosoma and waist segments appearing matt. First gastral tergite unsculptured, smooth, and shiny. Pilosity and pubescence greatly reduced: head with few pairs of moderately long, standing hairs, anterior pronotum with one long pair, waist segments sometimes with one long pair each, and sometimes first gastral tergite with one long pair; appressed pu- bescence present everywhere on body, but noticeable only on antennae, cephalic dorsum, legs, and first gastral tergite. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with appressed hairs. Body strongly bicoloured with dark brown to black gaster contrasting with light brown to reddish brown remainder. Distribution and biology. So far, T. uelense is known from a few collections in savannah habitats throughout a relatively wide geographical range from West to Central Africa (Fig. 3). The known distribution spans Guinea through Ghana and Nigeria to the northeast of the D. R. Congo close to South Sudan and Uganda. Compared to most other Afrotropical Tetramorium species, there is a wealth of information about the natural history of T. uelense (Longhurst, 1979). Longhurst et al. (1979) provided important observation data about nests, foraging, recruitment, and predation on termites. Tetramorium uelense live in subterranean nests difficult to locate without observing foraging workers. At least in the area observed by Longhurst et al. (1979), the main prey of T. uelense consisted of various species of Microtermes Wasmann, and T. uelense exerted great predation pressure on these small termites. Scouting is performed by solitary workers that search the leaf litter, fallen grass stems or pieces of wood for prey. After locating termites the scouts return to the colony for recruitment of groups between 10 to 30 workers. These groups locate, immobilise, and retrieve the prey. For more details refer to Longhurst et al. (1979).
Discussion. Tetramorium uelense can be easily distinguished from the remainder of the T. decem species group. The presence of longitudinally rugose sculpture on the dorsum of the mesosoma separates T. uelense immediately from T. decem, T. ultor, and T. venator. In the latter three the mesosomal dorsum is completely unsculptured, smooth, and very shiny. The only other species with sculpture on the dorsum of the mesosoma, which could be confused with T. uelense, is T. raptor. Nevertheless, both are well separable in morphology and ecology. Most obviously, T. uelense is a larger species (WL 0.98-1.06) with distinct bicolouration while T. raptor (WL 0.88-0.93) is smaller and a uniform dark brown colour. In addition, T. uelense has longer and better developed propodeal teeth (PSLI 16-18) compared to T. raptor (PSLI 10-11), even though this might be difficult to see and may require measurements to confirm. Another, more visible character is the sculpture on the mesosomal dorsum, which is strongly longitudinally rugose with distinct punctate ground sculpture in T. uelense versus longitudinally rugulose with very little ground sculpture in T. raptor. Also, the lateral pronotum of the latter is mostly unsculptured, smooth, and shiny while in T. uelense the lateral pronotum is strongly rugose with conspicuous ground sculpture.
Variation. Despite the broad distribution range, we did not observe any significant intraspecific variation in T. uelense. [Note: the GPS data of the type locality was not provided by the locality label or the original description. The data presented above is based on our own geo-referencing of the Shiloh locality located in Matabeleland North province. Consequently, it should be considered an approximation and not the exact position of the type locality.]
Worker measurements ( Worker description. Head much longer than wide (CI 77-82); posterior head margin weakly concave. Anterior clypeal margin with distinct, but often shallow median impression. Frontal carinae strongly developed and noticeably raised forming dorsal margin of very well-developed antennal scrobes, curving down ventrally and anteriorly halfway between posterior eye margin and posterior head margin and forming posterior and ventral scrobe margins; antennal scrobes very well developed, deep and with clearly defined margins all around, median scrobal carina absent. Antennal scapes short, not reaching posterior head margin . Eyes very large . Mesosomal outline in profile relatively flat, long and low (LMI 32-35), moderately marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove present and distinct, but relatively shallow. Propodeum armed with short, tri-angular, and mostly blunt teeth (PSLI 10-13), propodeal lobes short, triangular, and usually blunt, in profile usually longer and more voluminous than propodeal spines. Tibiae and femorae strongly swollen. Petiolar node nodiform with moderately rounded antero-and posterodorsal margins, in profile around 1.1 to 1.2 times higher than long (LPeI 86-92), anterior and posterior faces approximately parallel, anterodorsal and posterodorsal margins situated at about same height and equally angled, petiolar dorsum weakly convex; node in dorsal view around 1.1 to 1.2 times longer than wide (DPeI 79-86), in dorsal view pronotum between 2.0 to 2.2 times wider than petiolar node (PeNI 46-50). Postpetiole in profile globular, approximately 1.2 to 1.4 times higher than long (LPpI 73-81); in dorsal view around 1.3 times wider than long (DPpI 126-132), pronotum approximately 1.4 to 1.5 times wider than postpetiole (PpNI 60-71). Postpetiole in profile appearing less voluminous than petiolar node, postpetiole in dorsal view between 1.3 to 1.5 times wider than petiolar node (PPI 130-145). Mandibles and clypeus usually fully unsculptured, smooth, and shining; cephalic dorsum between frontal carinae mostly unsculptured and shiny, median ruga present and distinct, cephalic dorsum also puncticulate to punctate throughout its length, close to posterior head margin especially pronounced; scrobal area unsculptured, smooth, and very shiny; lateral head ventral of antennal scrobe mainly reticulate-rugose; ground sculpture on head usually weak to absent. Dorsum of mesosoma mostly unsculptured, smooth, and shiny with scattered punctures, rarely with few traces of rugulae; lateral mesosoma mostly unsculptured and shiny, posteriorly irregularly rugose and conspicuously reticulate-punctate. Petiolar node and postpetiole only weakly sculptured, laterally usually superficially rugulose and punctate on lower half and more unsculptured on upper half, node dorsally mostly smooth; postpetiole mostly unsculptured, smooth, and shiny with scattered punctures. First gastral tergite unsculptured, smooth, and shiny. Pilosity and pubescence greatly reduced: head with few pairs of moderately long, standing hairs, anterior pronotum with one long pair, waist segments sometimes with one long pair each, and sometimes first gastral tergite with one long pair; appressed pubescence present everywhere on body, but noticeable only on antennae, cephalic dorsum, legs, and first gastral tergite. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with appressed hairs. Body uniformly brown, appendages often lighter.
Distribution and biology. Tetramorium ultor is widespread in eastern and southern Africa (Fig. 3). It is distributed from Kenya south to Mozambique, and also found in Zambia and Zimbabwe. Most localities are tropical dry forest habitats or miombo woodland. Also, T. ultor seems to be a ground-active species nesting in or under rotten logs and is likely termitophagous like the other group members.
Discussion. Since Bolton (1976) synonymised T. ultor under T. decem, almost all of the material of T. ultor examined here was identified and/or labelled as T. decem prior to this study. However, after careful examination of all the available material, we have come to the conclusion that T. ultor is distinctive enough to merit species status. Tetramorium ultor is smaller (WL 0.85-0.96), has shorter propodeal teeth (PSLI 10-13), a lower petiolar node, around 1.1 to 1.2 times higher than long (LPeI 86-92), and is of uniform light brown to chestnut brown body colouration. By contrast, T. decem is larger (WL 1.02-1.16), has longer propodeal spines (PSLI 17-19), a higher petiolar node, in profile around 1.2 to 1.3 times higher than long (LPeI 77-82), and is conspicuously bicoloured. In addition, both species share most of their distribution range without any intermediate forms. Furthermore, T. ultor is unlikely to be confused with T. raptor and T. uelense since the latter two have a conspicuously rugose/ rugulose promesonotum, which is completely unsculptured, smooth and shiny in T. ultor. The last species of the group, T. venator, is the one most similar to T. ultor, and both species are allopatric. However, both species can be separated by eye size, colour, and a different habitat choice. Tetramorium venator has larger eyes (OI 37-40) and is of a much darker brown than T. ultor, which has smaller eyes (OI 33-36) and is of a lighter brown. In addition, the latter species is more arid-adapted, occurring in woodlands and dry forests while T. venator seems to be a forest specialist found in primary, secondary, or disturbed rainforests. We consider the above arguments as sufficient to justify the heterospecificity of both species. Further arguments are provided below in the description of T. venator.
Variation. Based on the available material, we did not observe any intraspecific variation in T. ultor. Mesosomal outline in profile relatively flat, long and low (LMI 33-37), moderately marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove present and distinct, but relatively shallow. Propodeum armed with very short, triangular, and moderately acute teeth (PSLI 9-12), propodeal lobes short, triangular to rounded, and usually blunt, in profile more or less of same length as propodeal teeth and appearing more voluminous than propodeal spines. Tibiae and femorae strongly swollen. Petiolar node nodiform with moderately rounded antero-and posterodorsal margins, in profile between 1.0 to 1.2 times higher than long (LPeI 90-100), anterior and posterior faces approximately parallel, anterodorsal and posterodorsal margins situated at about same height and equally angled, petiolar dorsum usually conspicuously convex, sometimes only weakly so; node in dorsal view around 1.2 to 1.3 times longer than wide (DPeI 76-85), in dorsal view pronotum between 2.0 to 2.2 times wider than petiolar node (PeNI 45-51). Postpetiole in profile globular, approximately 1.2 times higher than long (LPpI 80-86); in dorsal view around 1.2 times wider than long (DPpI 115-124), pronotum approximately 1.5 to 1.6 times wider than postpetiole (PpNI 63-67). Postpetiole in profile appearing less voluminous than petiolar node, postpetiole in dorsal view between 1.3 to 1.5 times wider than petiolar node (PPI 130-144). Mandibles and clypeus usually fully unsculptured, smooth, and shining; cephalic dorsum between frontal carinae mostly unsculptured and shiny, median ruga present and distinct, cephalic dorsum also puncticulate to punctate across its length, close to posterior head margin especially pronounced; scrobal area unsculptured, smooth and very shiny; lateral head ventral of antennal scrobe mainly reticulate-rugose; ground sculpture on head usually weak to absent. Dorsum of mesosoma mostly unsculptured, smooth and shiny with scattered punctures, rarely with few traces of rugulae; lateral mesosoma mostly unsculptured and shiny, posteriorly irregularly rugose and conspicuously reticulate-punctate. Petiolar node and postpetiole only weakly sculptured, laterally usually superficially rugulose and punctate on lower half and more unsculptured on upper half, node dorsally mostly smooth; postpetiole mostly unsculptured, smooth and shiny with scattered punctures. First gastral tergite unsculptured, smooth, and shiny. Pilosity and pubescence greatly reduced: head with few pairs of moderately long, standing hairs, anterior pronotum with one long pair, waist segments sometimes with one long pair each, and sometimes first gastral tergite with one long pair; appressed pubescence present everywhere on body, but noticeable only on antennae, cephalic dorsum, legs, and first gastral tergite. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with appressed hairs. Head, mesosoma, waist segments, and gaster uniformly very dark brown to black, appendages of lighter brown.

Tetramorium venator
Etymology. The name of the new species is Latin and means "hunter" referring to the predatory lifestyle of T. venator. The species epithet is a nominative noun, and thus invariant.
Distribution and biology. Tetramorium venator is the most widespread and abundant species of the group. It is found throughout much of the equatorial forest belt from Liberia in the west to Kenya in the east (Fig. 3). Even though there was no material from Benin, Togo, Nigeria, Equatorial Guinea or South Sudan available for this study, we expect that T. venator will be found in most or all of these countries. Based on the available data, this species lives in the leaf litter stratum of primary, secondary, or disturbed rainforests. Additionally, T. venator seems to be found at lower elevations in West and Central Africa, but also occurs at mid elevations further east in the eastern D.R. Congo, Tanzania, and Kenya, where it reaches its highest known elevation at the type locality at 1448 m. Based on unpublished stable isotope data from the type series, T. venator is a predatory species, and we assume that it feeds on termites. This is supported by some series from Cameroon that were collected while foraging in the nests of Cubitermes Wasmann.
Discussion. Despite being common and collected fairly often prior to this study, most of the material of T. venator was identified and labelled as T. decem. Indeed, more than 90% of all the material listed as the latter species at the beginning of our revision turned out to be T. venator. Nevertheless, our revision shows that they are clearly not conspecific. Tetramorium venator is smaller in size (WL 0.87-0.98), has larger eyes (OI 37-40), shorter propodeal teeth (PSLI 9-12), a lower petiolar node (LPeI 90-100), and has a uniform body colouration. By contrast, T. decem is larger (WL 1.02-1.16), has smaller eyes (OI 32-34), longer propodeal spines (PSLI 17-19), a higher petiolar node (LPeI 77-82), and is distinctly bicoloured. Also, T. venator is a rainforest species while T. decem lives in savannah or woodland.
The abovementioned very large eyes of T. venator separate it also from T. ultor, which has smaller eyes (OI 33-36). In addition, T. ultor is also of a much lighter colour, usually light brown to chestnut brown, and prefers dry forest or woodland habitats. It should be noted, however, that T. ultor and T. venator are morphologically very close to each other and differ significantly only in eye size, colour and habitat preference. They could represent different ecotypes of the same species, one adapted to more shaded and humid forest versus one specialised to more arid savannah, woodland, and dry forest. Nevertheless, if this was true, then we would see some intermediate forms in transitional habitats, and there are none at present. As a matter of fact, T. venator is also found in secondary and disturbed rainforests. The type series was collected in a highly disturbed rainforest fragment in Kenya and the material from Gombe in Tanzania is from a rainforest-woodland mosaic. Both species are also separated by the Great Rift Valley, which separates different faunistic sub-regions of the Afrotropical region. We consider T. venator as a faunal element of the Guineo-Congolian forest zone, while we believe T. ultor is a species of the arid corridor running from East to Southern Africa. Based on the available material and African biogeography in general, we conclude that our two species hypothesis is more likely.
Furthermore, T. venator cannot be misidentified with either T. uelense or T. raptor since both possess strongly developed rugulose/rugose sculpture on the promesonotal dorsum that is absent in T. venator. At present, T. venator overlaps in its distribution with T. uelense and T. raptor in West and Central Africa. We think it might also overlap with T. decem and T. ultor in East Africa, even though it currently seems as if they are widely separated geographically. However, since the sampling is very patchy, especially in East Africa, much more T. decem and T. ultor material is likely to be collected with further inventories, and these two species will be found in close proximity to T. venator. Never- theless, the latter species is restricted to more humid forest habitats, whereas T. decem and T. ultor clearly prefer more arid savannah, grassland, woodland and tropical dry forest.
Variation. Intriguingly, even though T. venator is very broadly distributed in Equatorial Africa, there seems to be no significant intraspecific variation.