A peculiar new species of the genus Tetrasticta Kraatz (Coleoptera, Staphylinidae, Aleocharinae) from Peninsular Malaysia

Abstract Tetrasticta gnatha sp. n., collected under the bark of a rotten fallen tree in Peninsular Malaysia, is described. A habitus photograph, line drawings of diagnostic characters, and a diagnosis are provided. The new species is readily distinguished from all known congeners by having long mandibles, and long, curved maxillary palpi.

Previously, three species of Tetrasticta were known from Malaysia (Cameron 1943;Maruyama 2004;Pace 2008), one of which was recorded from Peninsular Malaysia (Maruyama 2004).

Materials and methods
The technical procedures, terminology, and other methods used here are given in detail in Maruyama (2006) and Yamamoto and Maruyama (2012). In the descriptions, the numbers of macrosetae are those on one side of the body. The macrosetae on tergite VIII and sternite VIII are illustrated only on one side of the segments. All measurements in the paper are given in millimetres as follows: minimum length-maximum length (mean±SD). Most of the type specimens including the holotype are preserved at the Kyushu University Museum, Fukuoka, Japan. Type material. Holotype: male, "Nr. Kenyir Lake / Kuala Terengganu St. / W. MA-LAYSIA / 1-III-2002 / Tomoyuki TSURU leg.". Paratypes: 1 male, 1 female, 9 unsexed specimens, same data as the holotype.
Measurements. BL, ca. 3.7-5.6 (4. Diagnosis. 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.
Bionomics. Dr. T. Tsuru collected all the specimens from a rotten log about 50 cm in diameter lying in the rainforest.

Distribution. Malaysia (Peninsula).
Remarks. 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 2004Maruyama 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 T. gnatha and these genera. Although T. 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 T. gnatha were found under bark. Since no behavioral observations were made, termitophily of T. gnatha remain uncertain. The long mandibles in both sexes and the flattened body suggest a predatory life under bark.
Etymology. The Greek gnathos means jaw, for the exceptionally long mandibles.