Tapinoma pithecorum

Identification
Tapinoma pithecorum is easily separable from other nanitic tropical Tapinoma species – both morphometrically (table I)and by subjective visual inspection. It differs from Tapinoma melanocephalum by a larger postocular index, a shorter scape and 3rd funiculus segment as well as smaller eye length and smaller or absent clypeal excavation. With all measurements in mm, a simple discriminant D(2) = 152.56 × PoOc – 56.444 × SL – 12.5 offers a perfect separation – with 98.5 % of the 65 specimens classified with posterior probabilities of p  > 0.90 (figure 10). D(2) is – 3.095 ± 1.014 [– 5.434, – 0.608] in 51 workers of T. melanocephalum and 2.419 ± 0.945 [0.608, 3.692] in 14 workers of T. pithecorum. According to photo evaluation (table I) it differs from five specimens of Tapinoma indicum by longer scape and funiculus segments, shorter postocular distance, absence of clypeal excavation and the color contrast between mesosoma and gaster. These specimens of T. indicum included the type specimen from Poona (India) (www.antweb.org: CASENT0909774). A synonymy with Tapinoma minutum is also excluded. The type specimen of homogenously colored T. minutum from Sydney (Australia) (www.antweb.org: CASENT0915549) has according to photo evaluation a much longer scape and a much smaller postocular index (table  I) and it shows no color contrast on whole body. The clear separation of the four species is summarized by a principal component analysis (figure 2).

Distribution
Tropical to subtropical species of apparently Orientalic, Indo-Australian and Australasian origin with probably weak tramp species potential and globally much rarer than T. melanocephalum (7 against 76 samples). Outdoor populations are known so far from Oman: Salalah [17.02°N,54.11°E, 9 m], Pakistan: Balakot [34.55°N, 73.35°E, 1070 m], India: Khalgat [22.16°N, 74.45°E, 200 m], Australia: Christmas Island [10.48°S, 105.65°E, 120 m], Fiji: Penang [17.364°S,178.161°E, 36 m] and Malaysia: Cameron Highlands [4.47°N,101.37°E, 1400 m]. Greenhouse populations in the temperate zone are so far only known from Germany: Hannover [52.381°N, 9.771°E, 58 m].

Distribution based on Regional Taxon Lists
Indo-Australian Region: Christmas Island, Fiji, Malaysia. Oriental Region: India, Pakistan. Palaearctic Region: Germany, Oman.

Nomenclature

 * . Tapinoma pithecorum Seifert, 2022: 39, figs. 4, 6, 7, 9, table 1 (w.) GERMANY.

Type Material

 * Holotype plus two paratype workers labeled “GER: Hannover, Zoo, Affenhaus, Nest in Rindenmulch, leg. STELLMACHER 2002.09.05”; depository SMN Görlitz.
 * Eight paratype workers labeled “INDIAN OCEAN: Christmas Is. I–IV. 1933.”; depositories SDEI Müncheberg (6 paratypes) and SMN Görlitz (2 paratypes). One paratype worker labeled “INDIA: M. P. KHALGHAT, 200 m 1–13–62” and “Collectors: E. S. ROSS, D. Q. CAVAGNARO”; depository NHM Basel. One paratype worker labeled “Balakot 3500', Kagan Valley 24. V.” and “Pakistan 1974, C. BARONI  URBANI”; depository NHM Basel. One paratype worker labeled “Penang 5.III.27.”,  “Dr. EIDMANN  legit”  and  “Nat.Hist.Mus Basel–1972. coll. H. EIDMANN”; depository NHM Basel. One paratype worker labeled  “Oman, Dhofar, Salalah, 18.XI.2017, 9 m, M. R. SHARAF” and “ANTWEB CASENT 0922866”; depositoryCAS San Francisco. One paratype worker labeled“CASENT0095240 ANTC2676”,  “WEST MALAYSIA:Cameron Highlands 500 m below Tana Rana 6.X.–.XXII.2001Traps A & B O.P. CHOO” depository CAS San Francisco.

Description
Worker

Minute, mean CS=451 µm. Head elongated, CL / CW 1.142. Postocular index larger than in T. melanocephalum, PoOc / CL 0.497. Hind margin of vertex usually slightly excavated, ExOcc / CS 0.66 % (compare figures 4 and 5). Anterior clypeal margin in contrast to T. melanocephalum not or only very slightly excavated, ExCly / CS 0.44 % (figure 6). Minimum distance of the inner margins of antennal socket rings smaller than in T. melanocephalum, dAN / CS 0.324. Scape and 3nd segment of antennal funiculus much shorter than in T. melanocephalum, SL / CS 0.846, Fu3 / CS 9.69 % (figure 9). Second funiculus segment very short, always shorter than wide, Fu2 / CS 7.36 %, IFu2 0.759. Maximum eye diameter notably smaller than in T. melanocephalum, EL / CS 0.247. Mesosoma more compact, with a larger width and shorter length than in T. melanocephalum, MW / CS 0.667, ML / CS 1.158. Pubescence hairs on all body surfaces longer and shaggier than in T. melanocephalum but of similar density (figures 4–5). Head and mesosoma medium to blackish brown. Gaster, antennae and legs always notably lighter, in dried specimens very pale yellowish or very pale brownish. Accordingly, it shows basically the same light-dark contrasts as T. melanocephalum but it is as a whole darker (figures 7–8). It appears unlikely that gaster and appendages are translucent in living ants as it is observed in T. melanocephalum but this remains to be studied.

Etymology

Meaning “belonging to the apes” referring to finding of the first sample in the ape house of the Hannover Zoo.

Measurements

CL. Maximum cephalic length measured between points A and B. A is the posteromedian margin point of head capsule. B is an imagined median point situated at the same transversal level as the most anterior points of clypeus left and right of clypeal excision. Bilateral asymmetries are averaged. CS. Cephalic size. Arithmetic mean of CL and CW. CW. Maximum cephalic width. dAN. Minimum distance of the inner (centripetal) margins of antennal socket rings which is best measurable in dorsofrontal view (figure 1). EL. Eye length: maximum diameter of the compound eye over all structurally defined ommatidiae. Bilateral mean ExCly. Maximum depth of anteromedian clypeal excision as it appears in frontodorsal view and with median line of head positioned perpendicular in the visual field. Bilateral asymmetries are averaged (figure 1). ExClyW. Width of clypeal excision at the level of the base centers of the two most apical and largest setae. Note: This is a well-measurable standard character in a majority of Tapinoma species (figure 1). Yet, due to the very shallow shape or even complete absence of clypeal excision in the species group considered here, ExClyW is difficult to be measured or, when ExCly = 0, not defined. To circumvent this problem, the distance between the base centers of the two most apical and largest setae was taken as substitute data. ExOcc. Depth of excavation of posterior vertex. Procedure: adjust head in measuring position for CL, focus both posterior corners of vertex until they form a sharp contour, adjust them to equal horizontal level within the visual field and superimpose the corners with the horizontal line of the cross-scale. Change the focal level until the median part of posterior vertex forms a sharp contour. Read the depth. Fu2. Median length of second funiculus segment in dorsal view. Dorsal view is given when the swiveling plane of 1st funiculus segment is positioned in the visual plane). Take care to really measure median length (the segment's sides have unequal length!) and to recognize the real distal margin of the segment. The latter has a very thin cuticle, frequently producing a narrow, shining ribbon that seems to be, by optical impression, demarcated from the rest of the segment. The median line of the segment is visualized by center of the patch reflecting the coaxial light. Fu2W. Median width of second funiculus segment in dorsal view. Use of transmitted-light is important visualize the real cuticular surface. IFu2. Index Fu2 / Fu2W. ML. Mesosoma length from the caudalmost point of lateral metapleuron (posterior measuring point) to rear margin of anterior pronotal fringe (anterior measuring point). This character is often not measurable because the anterior measuring point is concealed by the head. In this case, with mesosoma in estimated adjustment for measuring a correct ML, the distance from posterior measuring point to dorsal point of pronotal-mesonotal border is measured and this value multiplied by 1.3422 (n = 9). MPGr. Depth of metanotal groove / depression in lateral view. The upper reference line extends between the highest points of mesonotum and propodeum perpendicular to which depth measuring is performed. MW. Maximum pronotal width. nExCly. Bilateral sum of pubescence hairs and smaller setae protruding at a few micron across margin of clypeal excision. The two setae at the lateral margin of the excision are not counted. PoOc. Postocular distance: distance from the transversal level of posterior eye margin to hind margin of head measured in median line. Bilateral asymmetries are averaged. SL. Scape length excluding articulatory condyle.