Akarbatrus diversicornis, Löbl, 2009

Löbl, Ivan, 2009, Akarbatrus gen. nov., an unusual Batrisitae (Coleoptera: Staphylinidae: Pselaphinae) from Sumatra, Acta Entomologica Musei Nationalis Pragae 49 (2), pp. 661-670 : 667-669

Akarbatrus diversicornis sp. nov.

Type material. HOLOTYPE: male, ‘ INDONESIA: Sumatra, W. Sum., Padangpajar, 600m, 17.xi.1989, Agosti, Löbl, Burckhardt # 20’ ( MHNG).

Diagnosis. Pronotal, elytral and abdominal pubescence long. Antennomeres 2 and 3 long, antennomere 8 extended apicolaterally to form a process. Head with U-shaped sulcus. Vertex not raised and not modified, with visible foveae in dorsal view. Pronotal excavation deep and smooth, not delimited by ridges, without setal patches and processes. Elytra without humeral tubercles, sutural striae completely reduced. Aedeagus lacking apophyses.

Description. Length 1.35 mm. Body uniformly reddish brown, appendages lighter than body.

Head rounded triangular, with eyes 0.35 mm wide, wider than long, densely and coarsely punctate except on and between antennal tubercles. Frontal lobe strongly inflexed and weakly convex, with rounded anterior margin and Y-shaped carina. Frons depressed between antennal tubercles, lacking foveae. Pubescence on frons fairly short, recumbent, directed forward. Pubescence behind level of antennal tubercles very short, directed apically. Pubescence near eyes long, curved, directed latero-anteriorly. Antennal fossae reaching level of median third of head length, open toward eyes. Frontoclypeus narrow, overlapped by frontal lobe. Ocularmandibular carinae extended to anterior eye margins, not extended along eyes. Vertex not modified sexually, flattened, with mesal carina extended from neck to level of anterior eye margins. Vertexal foveae situated dorsally, about at level of eye centres, interval between them about twice as large as interval between fovea and lateral head margin. U-shaped sulcus shallow, faint anteriorly. Posterior part of vertex vertical and narrow. Eyes fairly small, prominent, situated in basal half of head length (without neck), not emarginate, multifaceted, facets small. Tempora arcuate, long, in dorsal view longer than eyes. Gular area convex, very finely punctate and bearing recumbent pubescence.

Neck narrowly exposed in dorsal view. Ventral side of neck with microsculpture consisting of transverse striae.

Antennae long, reaching behind abdominal tergite 1. Relative length (basal stalk included) / width of antennomeres as: I 14/9: II 12/6.5: III 14/6: IV 14/6: V 17/6: VI 16/6: VII 18/7: VIII 17/10: IX 15/7: X 13/8: XI 33/10. Scape cylindrical, about 1.5 times as long as wide, with apical margins slightly prominent, lacking apical fovea. Antennomere 2 to 6 subcylindrical. Antennomere 7 slightly curved and slightly thickened apically.Antennomere 8 sexually modified, asymmetrical, slightly curved, thickened apically, outer apical angle prominent laterally, forming sharp tooth bearing long setae. Club loosely 3-segmented, antennomere 9 distinctly shorter than antennomeres 8 or 7, as wide as antennomere 7. Antennomeres 9 and 10 widest at their respective middle. Antennomere 10 shorter and slightly narrower than antennomere 9. Antennomere 11 subcylindrical in basal half, tapering apically, somewhat longer than combined length of antennomeres 9 and 10, about 3.3 times as long as wide.

Pronotum strongly sexually modified, slightly wider than head and wider than long, at widest point 1.7 times as wide as at base. Anterior margin truncate, not extended over neck, about as wide as basal margin. Contours pyriform. Basal margin transverse. Narrow antebasal area almost even, without foveiform impressions, lacking foveae. Laterobasal foveae large, situated on vertical, smooth areas concealed in dorsal view. Median area of disc abruptly, deeply excavated. Contours of excavation rounded triangular, narrowed toward pronotal base. Excavation at widest point about 0.16 mm wide, separated by about 0.05 mm from anterior pronotal margin. Narrow basal part of excavation shallower than centre of excavation, parallelsided, with sharp margins, ending about 0.06 mm in front of basal pronotal margin. Surface of excavation glabrous. Lateral margins of excavation not raised. Pronotal disc raised to form low tubercle at each side of excavation at about mid-length of pronotum. Anterior surface of tubercles obliquely inclined toward shallow transversal impressions and each bearing row of horizontal setae. Mediolateral areas impressed and flattened, sharply delimited except in anterior portions. Discal punctation very fine. Pubescence long, curved, rather recumbent, admesal macrosetae absent. Hypomera convex, distinctly punctate, lacking ridges.

Elytra convex dorsally, combined 0.48 mm wide, as wide as long, strongly narrowed toward base. Basal sulcus and lateroapical cleft absent. Humeral areas weakly angulate, humeral tubercles absent, lateral contours arcuate. Sutural striae absent. Punctation consisting of very small, shallow punctures. Pubescence long, semi-erect, macrosetae absent. Metathoracic wings present.

Metasternum with shallow mesal impression, lacking foveiform impression, convex in admesal area, with arcuate, narrowly notched metacoxal process. Metasternal punctation sparse, even in length, pair of macrosetae present. Metacoxae moderately separated.

Mesotrochanter with narrow apophysis bearing apical seta, situated about in middle of posterior margin. Metatrochanters expanded apically and triangular, with short apical pubescence. Femora and tibiae lacking obvious sexual characters, tibiae lacking marcosetae. Metatibiae with apical tuft of robust setae. Tarsomeres 2 and 3 long, narrow, tarsomeres 2 flattened, tarsomeres 3 subcylindrical. Protarsomeres 2 and 3 subequal in length, tarsomere 2 hardly curved. Meso- and metatarsomeres 2 straight, shorter than tarsomere 3.

Abdomen with five exposed tergites, weakly and gradually narrowed apically. Tergite 1 horizontal, with single pair of basal foveae situated close to lateral margin. Tergites 2 to 4 lacking sharply defined lateral margins. Tergite 1 about 1.5 times as long as tergite 2, tergites 2 and 3 similar, slightly inflexed, tergite 4 almost as long as tergite 1, strongly inflexed, tergite 5 almost vertical. Abdominal punctation and pubescence similar to that on elytra, setae about as long as length of tergite 2, tergites 1 to 4 each with two pairs of macrosetae. Sternite 1 in middle weakly convex and about twice as long as sternite 2. Sternites 2 to 4 flattened in middle. Sternites 2 and 3 in middle equally long, each slightly longer than sternite 4.

Differential diagnosis. This species may be easily distinguished from A. jelineki sp. nov. by its unmodified vertex with exposed foveae, long antennomeres 2 and 3, modified antennomere 8, pronotum lacking high ridges, and elytra lacking sutural striae and humeral tubercles.

Habitat. Forest floor, under rotten bamboo.

Etymology. The species epithet refers to the distinctive shape of the antennae.

Comments. The aedeagus of the single available specimen was lost before being mounted on a slide. It was obviously similar in shape to that of A. jelineki sp. nov. However, it differed conspicuously by the absence of large apophyses.