Pengzhongiella daicongchaoi gen. et sp. n., a remarkable myrmecophile (Staphylinidae, Pselaphinae, Batrisitae) from the Gaoligong Mountains

Abstract A new genus and species, Pengzhongiella daicongchaoi, of the subtribe Batrisina (Batrisitae: Batrisini) is described from the Gaoligong Mountains, Yunnan, Southwest China. Adults were collected in a colony of Odontomachus monticola, and presented reduction of certain external characters and elongate appendages relating to myrmecophily. Description and illustrations of the habitus and major diagnostic features of the new taxon are provided; a brief discussion of its taxonomic placement is included. The new species also represents the first record of a Pselaphinae in association with an Odontomachus ant.

During a recent (April 2013) expedition made to the south Gaoligong Mountains in Yunnan, South China, an unusual batrisine was collected from a nest of Odontomachus monticola Emery, and presented remarkably elongate appendages and reduced foveae on the head, pronotum, and elytra. Despite the inadequate knowledge of the Asian Batrisitae, this species is readily recognized as new, though it cannot be placed in any described genus. We here establish a new genus, Pengzhongiella gen. n., for this unusual beetle, and provide a formal description. So far, no pselaphine has been recorded to live with Odontomachus ants.

Material and methods
The type series is housed in the Insect Collection of Shanghai Normal University, Shanghai, China (SNUC).
The collection data of the referred material are quoted verbatim. A slash (/) is used to separate different labels.
Measurements are in millimeters. The following abbreviations are applied: ALlength of the abdomen along the midline; AW-maximum width of the abdomen; EL-length of the elytra along the sutural line; EW-maximum width of the elytra; HL-length of the head from the anterior clypeal margin to the occipital constriction; HW-width of the head across eyes; PL-length of the pronotum along the midline; PW-maximum width of the pronotum. Length of the body equals HL + PL + EL + AL. Diagnosis. Head rectangular; lacking frontal rostrum. Pronotum with distinct lateral longitudinal sulci, disc barely convex; lateral antebasal foveae present; lacking median antebasal fovea, antebasal sulcus, antebasal tubercles, and basolateral foveae. Each elytron with three reduced basal foveae, lacking discal stria. Abdomen with basolateral foveae on tergites IV-VII; tergite IV the longest.
First two pairs of tarsi with second and third tarsomeres subequal in length, metatarsi with second tarsomeres longer than third ones.
Males with antennae, mesotibiae, and metatrochanters modified. Aedeagus with dorsal lobe largely fused to median lobe, paramere connected with median lobe by membrane.
Comparative notes. At this time Pengzhongiella cannot be placed near any genus, and seems to form an isolated group within Batrisina. The long appendages are rarely observed in Asian myrmecophilous batrisines. Coupled with the foveal pattern of the head, pronotum, and elytra, and other external characters, Pengzhongiella can be quickly separated from all known genera, especially the myrmecophilous members of the Asian Batrisitae. The exceptionally elongate antennae and legs are shared with the Sumatran Akarbatrus Löbl and the Australian Mossman Chandler. Both Akarbatrus and Mossman lack elytral basal foveae and the basal impression of the tergite IV. The former has a sexually modified pronotum in the male, while Mossman has the pronotum lacking lateral longitudinal sulci, with two antebasal tubercles, and an outer pair of basolateral foveae (Chandler 2001, Löbl 2009). Pengzhongiella has three punctiform foveae at the base of each elytron, the pronotum has a pair of lateral sulci and small antebasal foveae, while other sulci and foveae are completely reduced probably due to the myrmecophily, and tergite IV has a thin, deep basal sulcus.
Comparative notes. The characteristic antennae and aedeagus, combined with the generic characters (see 'Comparative notes' of the genus), provide a quick separation of the new species from all other members of the Batrisini.
Distribution. Southwest China: Yunnan. Host ant and biology. All individuals of P. daicongchaoi were collected from a colony of Odontomachus monticola nested inside a rotten fallen tree, at the side of a road in an evergreen broad-leaved forest (Fig. 4A-D). It's worthy of a note that a highly specialized species (lacking vertexal and pronotal median antebasal foveae) of Batraxis Reitter (22 ex.), one species of Batrisoschema Reitter (18 ex.), and one species of Harmophorus Motschulsky (5 ex.) were found in the same nest. Previously, no pselaphine has ever been reported living with members of the ant genus Odontomachus.