Holotype, pinned worker, GABON, Province Estuaire, F.C. Mondah, 21 km 331°NNW Libreville, 0°34.6'N, 9°20.1'E, 10 m, littoral rainforest, sifted litter (leaf mold, rotten wood), collection code BLF01742, 24.II.1998 (B.L. Fisher) [unique specimen identifier CASENT0248334] [CASC]. Paratypes, 16 pinned workers with same data as holotype [BMNH: CASENT0248332; CASC: CASENT0235154; CASENT0248333; CASENT0248335; CASENT0248336; CASENT0248337; CASENT0248338; CASENT0248339; CASENT0248340; CASENT0248341; CASENT0248342; MCZ: CASENT0248343; MHNG: CASENT0248344; NHMB: CASENT0248345].

CAMEROON: Campo Reserve, 2°36'N, 9°56'E, 40 m, 25.X.1991 (D.M. Olson); Mbalmayo, XI.1993 (N. Storck); Nkoemvon, 16.III.1980 (D. Jackson); Sud, P.N. Campo, 43.3 km 108°ESE Campo, 2.2825N, 10.2062E, 290 m, rainforest, 7.IV.2000 (B.L. Fisher); Sud, Res. de Faune de Campo, 2.16 km 106°ESE Ébodjé, 2.5678N, 9.8443E, 10 m, littoral rainforest, 9.IV.2000 (B.L. Fisher); Sud, Res. de Faune de Campo, Massif des Mamelles, 15.1 km 84°E Ébodjé, 2.5942N, 9.9595E, 180 m, rainforest, 4.IV.2000 (B.L. Fisher); Sud-Ouest, Bimbia Forest, 7.4 km 119°ESE Limbe, 3.9818N, 9.2625E, 40 m, rainforest, 14.IV.2000 (B.L. Fisher); GABON: Province Estuaire, Mondah Forest, near Libreville, 3.XII.1987 (J. Noyes); Province Estuaire, F.C. Mondah, 21 km 331°NNW Libreville, 0°34.6'N, 9°20.1'E, 10 m, littoral rainforest, 24.II.1998 (B.L. Fisher).

Tetramorium hecate differs from the other species of the group by the following character combination: antennal scapes relatively short (SI 73 - 77); eyes large (OI 27 - 31); petiolar node rectangular nodiform with anterodorsal and posterodorsal margins strongly angulate and situated at about the same height; mandibles unsculptured, smooth, and shining; petiole and postpetiole usually with weak sculpture; body colouration ranging from uniformly brown to head, mesosoma, waist segments yellowish to bright orange contrasting with very dark brown to black gaster.

(N=12). HL 0.58 - 0.67 (0.63); HW 0.54 - 0.64 (0.60); SL 0.41 - 0.49 (0.45); EL 0.15 - 0.20 (0.17); PH 0.28 - 0.36 (0.33); PW 0.42 - 0.52 (0.47); WL 0.69 - 0.83 (0.77); PSL 0.12 - 0.26 (0.20); PTL 0.20 - 0.26 (0.24); PTH 0.22 - 0.27 (0.25); PTW 0.17 - 0.22 (0.20); PPL 0.19 - 0.22 (0.21); PPH 0.22 - 0.28 (0.25); PPW 0.24 - 0.29 (0.27); CI 93 - 96 (94); SI 73 - 77 (76); OI 27 - 31 (28); DMI 58 - 63 (61); LMI 41 - 44 (42); PSLI 21 - 38 (32); PeNI 39 - 46 (43); LPeI 89 - 100 (94); DPeI 81 - 89 (84); PpNI 55 - 62 (57); LPpI 80 - 91 (86); DPpI 120 - 130 (126); PPI 129 - 142 (135).

Head longer than wide (CI 93 - 96); posterior head margin weakly concave. Anterior clypeal margin usually entire and convex, sometimes with very small median notch only visible under higher magnifications. Frontal carinae strongly developed, approaching or ending at posterior head margin. Antennal scrobes well developed, moderately shallow, and with clearly defined margins all around. Antennal scapes relatively short, not reaching posterior head margin (SI 73 - 77). Eyes large (OI 27 - 31). Mesosomal outline in profile weakly convex, moderately marginate from lateral to dorsal mesosoma; promesonotal suture and metanotal groove absent; mesosoma comparatively stout and high (LMI 41 - 44). Propodeal spines usually long to very long (PSLI 30 - 38), elongate-triangular to spinose, and acute, rarely spines reduced, short, elongate-triangular, and acute (PSLI 20 - 21); propodeal lobes short, triangular to elongate-triangular, and acute. Petiolar node in profile rectangular nodiform, approximately as high as long to weakly higher than long (LPeI 89 - 100), anterior and posterior faces approximately parallel, anterodorsal and posterodorsal margins situated at about the same height, anterodorsal and posterodorsal angles well-developed and rectangular, petiolar dorsum flat; node in dorsal view around 1.1 to 1.2 times longer than wide (DPeI 81 - 89). Postpetiole in profile globular to subglobular, approximately 1.1 to 1.2 times higher than long (LPpI 80 - 91); in dorsal view around 1.2 to 1.3 times wider than long (DPpI 120 - 130). Postpetiole in profile appearing less voluminous than petiolar node, in dorsal view approximately 1.3 to 1.4 times wider than petiolar node (PPI 129 - 142). Mandibles unsculptured, smooth, and shining; clypeus longitudinally rugulose, usually with three distinct rugulae, median rugula better developed than remainder, rugulae often with cross-meshes; cephalic dorsum between frontal carinae irregularly longitudinally rugose to reticulate rugose, posteriorly towards posterior head margin well reticulate-rugose, anteriorly towards posterior clypeal margin more regularly longitudinally rugose (usually with five to eight longitudinal rugae); scrobal area mostly unsculptured; lateral and ventral head longitudinally rugose to reticulate-rugose. Mesosoma laterally irregularly rugose, dorsally distinctly longitudinally rugose. Forecoxae unsculptured, smooth, and shining. Both waist segments laterally weakly, irregularly rugulose/rugose, dorsally mostly unsculptured, smooth, and shining. Postpetiole and gaster unsculptured, smooth, and shining. Ground sculpture generally faint to absent everywhere on body. Whole body with abundant, long, and fine standing hairs; first gastral tergite without appressed pubescence. Anterior edges of antennal scapes with suberect to erect hairs. Body colouration relatively variable, ranging from bicoloured with head, mesosoma, legs, and waist segments yellowish to bright orange contrasting with very dark brown to black gaster to whole body uniformly brown.

The name of the new species is inspired by the ancient Latin and Greek goddess “Hecate” or “Hekate”, also known as the “triple Hecate” or “three-faced Hecate”, and refers to the morphological variation in colouration and propodeal spine length observed in Tetramorium hecate. The species epithet is a nominative noun in apposition, and thus invariant.

The new species is currently only known from Cameroon and Gabon (Figure 7). All localities are situated at relatively low elevations ranging from 10 to 300 m, and most are either rainforests or littoral rainforests. Most of the available material was collected through litter sifting, which suggests that the preferred microhabitat of Tetramorium hecate is forest leaf litter.

Tetramorium hecate is unlikely to be misidentified with the other two species of the group. The most obvious difference between Tetramorium hecate and Tetramorium capillosum and Tetramorium tabarum is the shape of the petiolar node. In the latter two the node is nodiform with relatively rounded anterodorsal and posterodorsal margins, and, in addition, the posterodorsal margin is situated noticeably higher than the anterodorsal margin. In contrast, the node of Tetramorium hecate is nodiform, with clearly rectangular anterodorsal and posterodorsal margins, situated at about the same height. The second-most important character is antennal scape length. Tetramorium hecate has the shortest scapes of the three species (SI 73 - 77), strongly contrasting with the longer scapes of the other two species (SI 80 - 86). Furthermore, Tetramorium hecate is also a much smaller species with much larger eyes and very different colouration than Tetramorium capillosum (see description of the latter for more details). The very well developed antennal scrobes with clearly defined margins all around also separate Tetramorium hecate from Tetramorium tabarum since the scrobes of the latter are shallow and without posterior and ventral margins.

The new species shows an intriguing variation in colouration and propodeal spine length. At the initial sorting stage of this revision, we considered the material listed here as Tetramorium hecate to consist of three potential new species: a strongly bicoloured one with long propodeal spines (Figure 4A), a uniformly brown coloured one with long propodeal spines (Figure 4B), and a bicoloured one with shorter spines (Figure 4C). However, after examination of all the material, it became apparent that they belong to just one species having a moderate variation in colour, which includes a few specimens with exceptionally short propodeal spines. The differences in colouration appear distinct at first when looking at few specimens, but the examination of several hundred specimens showed that there is a gradual variation that ranges from strongly bicoloured to completely uniformly coloured with more than half of the specimens being intermediate. Generally, the spines are long to very long (PSLI 30 - 38) throughout the examined material of several hundred specimens, the exception being three specimens with very short propodeal spines (PSLI 20 -21). Apart from the spine length, however, no single character would justify a separation of these specimens from the main material. Consequently, we are very confident that all the material examined belongs to just one species.