Echinopla madli

Workers have been collected from a lower montane mixed dipterocarp forest, via fogging, and in a rainforest.

Identification
Zettel and Laciny (2015) - (worker). Predominantly black, very small, stout species, TL = 3.9–4.6 mm. Surface polyporous, dorsal margins of mesosoma with sharp tubercles. Head wider than long (CI = 104–115). Mesosoma roughly one fourth longer than pronotal width (MI 120–131), with sharp and deep mesometanotal suture. Pronotum hardly wider than head, if eyes excluded. Propodeum shorter than promesonotum. Petiole dentate, with 1–2 sharp teeth and 0–2 smaller denticles laterally below lateral spine. Gaster tergite 1 with relatively small pores and wide, strongly shiny interspaces; on disk subcumbent pilosity very sparse. Standing setae on dorsal surface of trunk, on legs and scape relatively short. Setae on tibia abundant, surpassing base of distally following setae.

Echinopla madli, Echinopla wardi, Echinopla brevisetosa, Echinopla fisheri and Echinopla angustata belong to a peculiar species group that is characterized by small body size (except Echinopla fisheri), black colour (lack of metallic lustre), and polyporous surface structures that resemble the pores of coral rocks (see Stitz 1938). Other species groups can be defined by different surface structures, at least on head and mesonotum, either fine puncturation, or striations consisting of sharp rugae, or high, truncate tubercles (“pedestals”) that give the specimens a spiny appearance. A peculiar character of E. madli is gaster tergite 1 that is hardly longer than wide and has a shiny, weakly pilose and sparsely pitted disc. These characters distinguish it immediately from closely related species in the region (Echinopla wardi, Echinopla brevisetosa, and Echinopla angustata). A similarly structured tergite 1 is found in Echinopla dubitata from Sulawesi, but this is a slender species with black tarsi, weakly developed appressed pilosity and long black standing setae.

We studied five workers of E. madli from three localities and noted a high variability. Whereas the paratype from Danum Valley (Sabah) largely agrees with the holotype from southern Thailand, further Sabah specimens from Poring Spring differ by largely black legs (except one callow worker), reduced median carinae on frons and clypeus, and some morphometric data (e.g., higher SI, lower CI). The examination of more material would be necessary to clarify the status of this population.

Distribution based on Regional Taxon Lists
Indo-Australian Region: Borneo, Indonesia, Malaysia. Oriental Region: Thailand.

Castes
Known only from the worker caste.

Nomenclature

 *  madli. Echinopla madli Zettel & Laciny, 2015: 103, figs. 1-4 (w.) THAILAND.

Worker
Holotype: TL 4.3; HW1 1.17; HW2 1.10; HL 1.07; EL 0.23; SL 0.91; SW 0.12; HaL 0.15; PML 0.76; PMW 1.11; PpL 0.59; PpW 1.04; PH 0.45; PL 0.38; PW 1.03; GL 1.24; GW 1.22. Indices: CI 110; SI 78; MI 122.

Paratype: TL 3.9; HW1 1.15; HW2 1.07; HL 1.00; EL 0.22; SL 0.89; SW 0.12; HaL 0.18; PML 0.72; PMW 1.09; PpL 0.59; PpW 0.98; PH 0.45; PL 0.38; PW 0.96; GL 1.17; GW 1.15. Indices: CI 115; SI 77; MI 120.

Non-type workers: TL 4.4–4.6; HW1 1.11–1.20; HW2 1.00–1.11; HL 1.07–1.11; EL 0.22– 0.25; SL 0.93–0.96; SW 0.13–0.14; HaL 0.11–0.13; PML 0.74–0.78; PMW 1.04–1.12; PpL 0.61–0.67; PpW 0.96–1.04; PH 0.46 (two measured); PL 0.36–0.38; PW 0.97–1.04; GL 1.26–1.37; GW 1.20–1.30. Indices: CI 104–108; SI 80–85; MI 129–131.

Structures: Head wider than long, subtrapezoidal, with slightly convex sides; dorsally and laterally polyporous, with closely set pores, posterolaterally with a few very small tubercles, matt; ventral surface smooth and shiny. Compound eye relatively small, moderately protruding, positioned slightly behind mid-length of head. Frons of type specimens with prominent median carina; frontal lobes chiefly horizontally oriented, completely covering antennal fossae in dorsal aspect, maximum distance of margins at mid-length, slightly greater than half of HW2. Clypeus of type specimens with prominent median carina, anterior margin weakly convex. Mandibles striate, masticatory margin with five teeth. Antennal scape moderately long, weakly s-curved, steadily widened from base to apex; antennomeres 8–10 slightly wider than long.

Mesosoma stout, length only 1.2 times pronotum width in type specimens; propodeum shorter than promesonotum. Surface polyporous, with closely set pores, dorsal margins with sharp tubercles. Pronotum with strongly developed angles, about as wide as head excluding eyes. Promesonotal suture weak, indicated by a convex row of deeper pits. Mesometanotal suture sharp, narrow and deep. In dorsal aspect mesosoma with waist-like incision in front of propodeum. Legs moderately long; femora not much widened.

Petiole wide and stout, subtriangular in lateral, strongly transverse in dorsal aspect; surface structure as on mesosoma; sharp dorsal crest bearing four sharp teeth medially and another two pairs of small denticles laterally; lateral tooth strongly developed; below lateral tooth with two sharp teeth and 0–2 (asymmetrical) small denticles. Gaster tergite 1 as wide as long, strongly convex, and completely covering the following tergites; hind margin moderately convex, finely serrate; surface polyporous, interspaces smooth and shiny; distances of pores mostly slightly larger than their diameters.

Pilosity: Head (except ventral surface), mesosoma, and petiole with dense, appressed white pilosity and moderately long white standing setae. Gaster tergite 1 with very sparse appressed pilosity on disc, but relatively dense at sides; standing setae anteriorly much longer than posteriorly. White standing setae on scape about as long as the setae on head. Legs with fine appressed pilosity. Femora with some long standing setae on flexor side. Pilosity on tibiae and first tarsomeres oblique, relatively long and dense.

Colour: Trunk black, without metallic shimmer, appearing grey by whitish pilosity. Antenna with black scape and base of funiculus, distal part testaceous. Mandible basally black, distally testaceous; other mouthparts yellowish. Legs of type specimens testaceous, but forecoxa black, apices of femora, tibiae and first tarsomeres infuscated. Legs of non-type specimens predominantly blackish.

Type Material
Type material. Holotype (worker, ) from Thailand, Satun Province, Thale Ban National Park, 10–16. III.1993, leg. Michael Madl. Paratype (worker, ) from Borneo, Sabah, Danum Valley, Field Centre, 525 m a.s.l., 4.963056°N; 117.802806°E, 16–26.VIII.2010, rainforest, Ant Course 2010, unknown collector.

Etymology
Dedicated to our colleague Michael Madl, Frauenkirchen, Austria, who collected the holotype specimen.

References based on Global Ant Biodiversity Informatics

 * Zettel H. and A. Laciny. 2017. Further additions to the taxonomy and distribution of the ant genus Echinopla (Insecta: Hymenoptera: Formicidae). Ann. Naturhist. Mus. Wien B. 119: 7-16.