Holotype: male, “Nr. Kenyir Lake / Kuala Terengganu St. / W. MALAYSIA / 1-III-2002 / Tomoyuki TSURU leg.”. Paratypes: 1 male, 1 female, 9 unsexed specimens, same data as the holotype.

Body: broad, somewhat flattened, shining (Fig. 1). Color: reddish brown; abdomen paler, with darker tergites V–VII; antennal segments I–IV, mouthparts, and legs reddish yellow; antennal segments V–XI brown. Head: large, as broad as pronotum, somewhat pentangular, moderately convex above, slightly wider than long; apical margin of clypeus rounded; frons produced, V-shaped; surface sparsely covered with minute, yellow setae; eyes prominent, length 0.64 times that of head. Antennae slightly longer than combined length of head and pronotum; segment I long, as long as combined length of segments II–V; segment II small, less than one-third of I; segment III small, shorter than II; segment IV extremely short, much wider than long, about half as long as III; segment V slightly wider than long; segments VI–X wider than long; segment XI oval, longer than wide; relative length of segments from base to apex: 31:7:6:3.5:9.5:10:10:10:10:10:22 (Fig. 2). Mouthparts: labrum much wider than long (W/L = 1.9), anterior margin widely emarginate. Mandibles slightly asymmetric, strongly curved, pointed apically (Fig. 3). Maxilla with a long and strongly curved maxillary palpus (Fig. 4). Mentum somewhat semicircular, much wider than long (W/L = 2.3); surface with 4 setae, and dozens of pores antero-medially. Pronotum: much wider than long, semicircular; disc with three pairs of small depressions (two pairs medially, one pair laterally); surface sparsely covered with yellow setae, and with approximately five bristles along lateral margin; each depression bearing a small bristle. Elytra: wider than long, subparallel-sided, rounded posterolaterally; surface moderately punctured and covered with yellow setae, and with four bristles laterally. Legs: rather short in length; relative lengths of tarsomeres from base to apex: 7:5:5:6:10.5 in foretarsus; 10:6:7:7:11 in midtarsus; 11:11:11:11:19 in hindtarsus. Abdomen: flattened, subpararell-sided, widest around segments IV and V; tergites III–VII sparsely covered with small setae.

Figure 1.

Habitus of Tetrasticta gnatha sp. n., female, dorsal view.

Figures 2–4.

Tetrasticta gnatha sp. n. 2 antennal segments I–V (right, dorsolateral view) 3 right mandible, male, dorsal view (hairs along inner side are those of prostheca) 4 right maxillary palpus, male, ventral view.

Male: tergite VIII generalized in shape; surface smooth, with approximately 5–6 macrosetae (Fig. 5). Sternite VIII generalized in shape, semicircular in dorsal view, with approximately 9–10 macrosetae (Fig. 7). Median lobe of aedeagus slightly narrowed apically in lateral view; inner sac with flagellum of copulatory piece not coiled (Figs 9–10); apical lobe of paramerite long, slightly dilated apically with four setae (Fig. 11).

Figures 5–12.

Tetrasticta gnatha sp. n. 5 male tergite VIII, dorsal view 6 female tergite VIII, dorsal view 7 male sternite VIII, ventral view 8 female sternite VIII, ventral view 9 median lobe of aedeagus, lateral view 10 ditto, ventral view 11 apical lobe of paramerite 12 spermatheca.

Female: tergite VIII generalized as in male, with approximately 7–9 macrosetae (Fig. 6). Sternite VIII generalized as in male, with approximately 9–10 macrosetae (Fig. 7). Spermatheca: moderately curved; border between basal and apical portions narrowly membranous; basal portion dilated apically, longer than apical portion, with prominent opening of spermathecal gland; apical portion oval, inner wall of apical part three-quarters to four-fifths densely striate (Fig. 12).

Measurements. BL, ca. 3.7–5.6 (4.4±0.5); HL, 0.70–0.91 (0.79±0.06); HW, 0.99–1.15 (1.07±0.06); AL, 1.68–1.97 (1.84±0.09); PL, 0.71–0.84 (0.77±0.05); PW, 1.12–1.36 (1.25±0.07); EL, 0.61–0.78 (0.70±0.05); EW, 1.22–1.56 (1.38±0.09); FTL, 0.64–0.81 (0.72±0.05); MTL, 0.78–0.97 (0.89±0.06); HTL, 0.89–1.16 (1.04±0.07); HW/HL, 1.22–1.52 (1.34±0.09); PW/PL, 1.58–1.68 (1.63±0.03). N = 12.

This new species is easily distinguished from other Tetrasticta species by having a large head, which is as wide as pronotum, flattened body with unique mouthparts (i.e., strongly curved maxillary palpi, especially segment II, and curved, sharply pointed mandibles). Furthermore, the species lacks a coiled flagellum inside the median lobe of the male aedeagus.

Dr. T. Tsuru collected all the specimens from a rotten log about 50 cm in diameter lying in the rainforest.

Malaysia (Peninsula).

Tetrasticta belongs to the Tetrasticta genus group, which comprises the genera Creochara Cameron, 1931, Cratoacrochara Pace, 1986, Ilarochara Pace, 1993, Aleonictus Kistner, 1997, Formicaenictus Kistner, 1997, and Myrmecosticta Maruyama, 2011 (Maruyama 2004; Maruyama et al. 2011). Pace (2010) synonymized Creochara with Tetrasticta, but did not provide an appropriate explanation; we do not follow this concept here. Tetrasticta gnatha is well characterized by the following character states: 1) long mandibles; 2) long, 3) curved segment II of the maxillary palpus; and 4) short, 5) simple flagellum of the median lobe of the aedeagus. Of these, states 2) and 3) are probably correlated with long mandibles, as also observed in the other aleocharines with long mandibles (e.g., some Lomechusini species). All other known species of Tetrasticta share a long, coiled flagellum of the median lobe of the aedeagus. The other character states fully coincide with those of Tetrasticta. A short, simple flagellum is also observed in Aleonictus and Formicaenictus in the same genus group, which are closely allied to Tetrasticta, but this state is apparently plesiomorphic, and cannot support a relationship between Tetrasticta gnatha and these genera. Although Tetrasticta gnatha is unique within the Tetrasticta genus group at first glance, we do not erect a genus for it. All of the type specimens of Tetrasticta gnatha were found under bark. Since no behavioral observations were made, termitophily of Tetrasticta gnatha remain uncertain. The long mandibles in both sexes and the flattened body suggest a predatory life under bark.

The Greek gnathos means jaw, for the exceptionally long mandibles.