Diacamma concentricum

Only known from the island of Palawan. All four records (Wheeler & Chapman 1925, Laciny et al. 2015) are from the island’s northern part.

Identification
Laciny et al. (2015) - Large, slender species (TL 14.1–15.3 mm). Trunk black, appearing grey by dense whitish pilosity. Trunk strongly striate from genae to petiole. Posterior of head longitudinally striate until hind margin; occipital margin moderately wide, laminate, ventrally short, terminating in small teeth. Clypeus with very dense puncturation and some distinct longitudinal rugae at least basally. Pronotum with concentric rugae. Striation on mesosoma sides slightly oblique. Petiole stout, its teeth long and far apart; subpetiolar process laterally carinate, a median carina absent or weakly developed, in lateral aspect with concave outline, anterior corner much longer than posterior one. Gaster tergite 1 with extremely fine puncturation.

Diacamma concentricum possesses concentrical rugae whereas those of Diacamma palawanicum are strictly longitudinal. In addition, the material examined differs slightly in the sculpture of the clypeus which is densely punctured in D. concentricum and with some distinct longitudinal rugae at base, whereas the clypeus of D. palawanicum has a reduced rugosity. The structures of the characteristic subpetiolar process are also similar; however, in examined specimens of D. concentricum its ventral surface is irregularly rugose and with an irregular pilosity, whereas in the D. palawanicum specimens it has a clear median carina and a very even pilosity consisting of short standing setae (this pilosity not visible in the syntype). Additionally, morphometric analysis showed that the specimen of D. palawanicum has a slightly more elongated head (CI 72 vs. CI 75–79 in D. concentricum) and shorter petiolar spines in comparison to D. concentricum. All these differences should be confirmed in more specimens, especially as the hitherto examined sample of D. concentricum shows considerable variability of overall size and the proportions of the petiolar spines (especially in SpDI), which may make comparisons difficult.

Distribution based on Regional Taxon Lists
Indo-Australian Region: Philippines.

Nomenclature

 *  concentricum. Diacamma palawanicum var. concentricum Wheeler, W.M. & Chapman, 1925: 64, pl. 2, figs. 7, 8 (w.) PHILIPPINES. Status as species: Laciny, Pal & Zettel, 2015: 99 (redescription). Senior synonym of sericeiventre: Laciny, Pal & Zettel, 2015: 99.

We have compared the original description of D. sericeiventre with our specimens of D. concentricum and conclude that it is the same species. The two taxa were described in the same year and the respective authors could not know about the other publication. Moreover, the type locality of D. sericeiventre is the same as one of the syntype localities of D. concentricum. There is some concern about the priority. According to the imprints of the volumes, Wheeler and Chapman’s publication was published on 21 September 1925, about three months earlier than Stitz’s (19 December 1925). An entry by the librarian of in Sitzungsberichte der Gesellschaft Naturforschender Freunde zu Berlin, volume 1923 notes that the book arrived in Vienna in February 1926, which serves as more evidence that the name concentricum has priority over sericeiventre.

Worker
Laciny et al. (2015) - (n = 4): TL 14.15–15.33; HW 2.30–2.54; HL 2.97–3.39; EL 0.60–0.68; SL 3.85–4.04; PH 2.07–2.28; PL 1.34–1.60; PW 1.28–1.46; SpD 0.85–1.03; SpL 0.64–0.76; WL 4.60–5.05; MTL 2.87–3.16. Indices: CI 75–79; SI 159–167; PI 65–70; SpDI 59–77; SpLI 45–54; EI 26–27.

Structures: Head elongated; sides parallel in front of eyes, strongly convex behind eyes. Eyes comparatively small. Very coarse rugae present from genae to petiole. Posterior of eyes, longitudinal rugae perpendicular to occipital margin. Occipital margin about as wide as one ruga, slightly laminate, ventrally short, terminating in small, rectangular or blunt teeth in lateral aspect. Clypeus with dense puncturation, matt, with additional striation in basal half; apex narrowly rounded. Mandibles with some fine, more or less reduced striation. Pronotum with concentrical, circular rugae. Striation on mesosoma sides slightly oblique. Posterior face of propodeum separated from sides by distinct carinae. Petiole stout, with very coarse striation and with rather long, slender spines. Subpetiolar process similar to that of D. palawanicum but distinctive: in lateral aspect with strongly concave outline, anterior tooth much longer than posterior one; in ventral view appearing arrow-shaped, sides sharply marginate anteriorly, a medial carina absent or weakly developed anteriorly, most surface with transverse or irregular rugulae; pilosity uneven. Gaster tergite 1 as the following tergites with very fine puncturation.

Pilosity: Standing setae on trunk mostly short, but those on clypeus, vertex, underside of head, and dorsum of petiole longer. Short appressed pilosity abundant, but more scarce on dorsum of head and pronotum, giving the specimen a grey appearance. Standing setae on scape and legs also short.

Colour: Trunk black, without metallic shimmer; on gaster posterior margins of tergites and apex more or less brown. Antennae black. Mandibles and most parts of legs dark reddish brown; forecoxa black, tarsi more or less infuscated.

Type Material
Laciny et al. (2015) - We tried to locate the type of Diacamma sericeiventre but it was not found by the curators in the collections of the Museum für Naturkunde Berlin (Viola Richter, in litt.), Senckenberg German Entomological Institut Müncheberg (Andrew Liston, in litt.), and Royal Saxon Academy of Forestry Tharandt (Ingo Brunk, in litt.).