Proceratium arnoldi Forel, 1913

Hita Garcia, Francisco, Hawkes, Peter G. & Alpert, Gary D., 2014, Taxonomy of the ant genus Proceratium Roger (Hymenoptera, Formicidae) in the Afrotropical region with a revision of the P. arnoldi clade and description of four new species, ZooKeys 447, pp. 47-86 : 57

Taxon classification Animalia Hymenoptera Formicidae

Proceratium arnoldi Forel, 1913 Figs 3E, 4B, 5C, 5F, 6D, 8A, 8B, 9A, 9B, 9C, 18

Proceratium (Sysphincta) arnoldi Forel, 1913: 210. [Combination in Sysphincta : Arnold 1915: 35; in Proceratium : Brown 1958b: 247; see also: Baroni Urbani and de Andrade 2003: 297]

Type material.

Holotype, pinned worker, ZIMBABWE, Bulawayo, (MHNG: CASENT0907203).

[Note: There are two known “type” specimens of Proceratium arnoldi , and there is some confusion about their labels and type status. De Andrade (in Baroni Urbani and de Andrade 2003) stated that the specimen from BMNH (CASENT0902425) labelled as syntype with the collection data "Bulawayo, S. Rhodesia, 29.III.1913, (G. Arnold)" is likely the specimen on which Arnold (1915) based his re-description and was probably never examined by Forel, even though it seems that both specimens belong to the same collection. We agree with de Andrade that this is not a type specimen].

Non-type material.

SOUTH AFRICA: Natal, N of Richard’s Bay, 28.40S, 32.14E, 26.I.-11.II.1991 (A. de Kock & J.D. Majer) (BMNH: CASENT0914281); ZIMBABWE: Bulawayo, S. Rhodesia, 29.III.1913, (G. Arnold) (BMNH: CASENT0902425).

Diagnosis.

The following character combination distinguishes Proceratium arnoldi from the other Afrotropical members of the Proceratium arnoldi clade: eyes very small, consisting of a single dark ommatidium (OI 3-5); head clearly longer than broad (CI 85-87); maculae on vertexal angles of head well developed and conspicuous; mesopleurae weakly to moderately inflated posteriorly; petiolar node high nodiform, anteroposteriorly compressed, with anterior face relatively straight; petiole in dorsal view between 1.0 and 1.2 times wider than long (DPeI 106-114); ventral process of petiole lamelliform, subrectangular, anteroventral corner blunt and posteroventral corner conspicuously projecting posteroventrally; abdominal segment IV around 1.2 to 1.3 times longer than abdominal segment III (ASI 116-132); head, mesosoma and petiole with mat of short decumbent to subdecumbent pubescence only, without any longer, fine suberect to erect hairs.

Worker measurements

(N=5). TL 3.27-3.56; EL 0.02-0.03; SL 0.49-0.52; HL 0.79-0.84; HLM 0.94-1.02; HW 0.69-0.71; WL 0.91-1.03; HFeL 0.59-0.67; HTiL 0.48-0.51; HBaL 0.38-0.46; PeL 0.33-0.34; PeW 0.35-0.38; DPeI 106-114; LT3 0.47-0.54; LS4 0.24-0.25; LT4 0.62-0.64; OI 3-5; CI 85-87; SI 60-63; IGR 0.38-0.41; ASI 116-132.

Worker description.

In full-face view head clearly longer than broad (CI 85-87), sides weakly convex, gently broadening posteriorly, vertex flat to weakly convex. Clypeus medially reduced, its anterior margin subconvex to slightly triangular, only slightly protruding anteriorly, not surrounding the antennal sockets and not medially impressed, antennal socket with broad torulus. Frontal carinae relatively very short and widely separated, not converging medially and strongly diverging posteriorly, partially covering antennal insertions; frontal carinae conspicuously raised anteriorly, much less so posteriorly. Eyes very small, consisting of one to four weak ommatidia (OI 5) and located on mid line of head. Mandibles elongate-triangular; masticatory margin of mandibles with one well developed apical tooth and a series of four denticles decreasing in size towards basal-most denticle. Mesosoma weakly to moderately convex in profile and approximately as long as the maximum head length including mandibles. Lower mesopleurae with well impressed sutures, no other sutures developed on lateral or dorsal mesosoma, mesopleurae weakly to moderately inflated posteriorly; propodeum in profile armed with very small, pointed or blunt teeth, propodeal lobes weakly to moderately developed, lamellate, subtriangular and blunt; declivitous face of propodeum between teeth and lobes concave; in posterodorsal view sides of propodeum separated from declivitous face by margin connecting propodeal lobes and propodeal teeth. Legs slender and elongate; pro- and mesotibiae with pectinate spurs; calcar of strigil without basal spine. Petiolar node in profile high, blocky nodiform, anterior face of petiole relatively straight, anterior and posterior faces approximately parallel, dorsum of node flat to very weakly convex; petiole in dorsal view between 1.0 and 1.2 times wider than long (DPeI 106-114), petiolar node in dorsal view clearly much broader than long; ventral process of petiole lamelliform, subrectangular, anteroventral corner blunt and posteroventral corner conspicuously projecting posteroventrally. In dorsal view abdominal segment III anteriorly broader than petiole; its sides diverging posteriorly; dorsum of abdominal tergum III with posteromedial, weakly developed, semitransparent, flat bulla below the integument; abdominal sternite III anteromedially with a marked subtriangular projection. Constriction between abdominal segment III and IV conspicuously impressed. Abdominal segment IV strongly recurved (IGR 0.38-0.41), conspicuously rounded on its curvature, especially posteriorly, abdominal tergum IV around 1.2 to 1.3 times longer than abdominal segment III (ASI 116-132); small, faint and semitransparent bulla situated posteromedially on abdominal tergum IV; remaining abdominal tergites and sternites relatively inconspicuous and curved ventrally. Whole body covered with dense mat of relatively short, decumbent to suberect pubescence without any abundant, much longer, suberect to erect, long, fine, standing hairs. Mandibles longitudinally rugose; most of body irregularly foveolate and/or punctate, sculpture best developed on cephalic dorsum, much weaker on remainder of body, especially weak, almost smooth on abdominal segments III and IV. Body colour uniformly yellowish to light brown.

Distribution and ecology.

At present, Proceratium arnoldi is only known from two localities in Zimbabwe and South Africa (Fig. 18). These localities are relatively far apart, but we expect that the species is more widespread and will be collected in the area between. Despite that it was described more than 100 years ago, there is no information available about its natural history.

Taxonomic notes.

Proceratium arnoldi is well recognisable within the clade. Its relatively thin head in full-face view (CI 85-87) groups it close to Proceratium carri (CI 85-86) and separates both from the other five species that have thicker heads (CI 91-95). However, Proceratium carri is not likely to be confused with Proceratium arnoldi . The latter possesses a mat of short decumbent to subdecumbent pubescence but without numerous much longer, fine standing hairs. These hairs are present in Proceratium carri , which also has a much longer abdominal segment IV in relation to abdominal segment III (ASI 156-159) than Proceratium arnoldi (ASI 116-132).

Variation.

We only observed some minor, very normal variation in body size in the known material of Proceratium arnoldi with the specimens from South Africa being somewhat larger (WL 0.98-1.03) than the ones from Zimbabwe (WL 0.91-0.92). Otherwise, there is no observable intraspecific variation.