A new species of Stigmatomma from Taiwan (Hymenoptera, Formicidae, Amblyoponinae)

Abstract Stigmatomma is the most speciose ant genus in the subfamily Amblyoponinae. In the present paper, the worker caste of a new species is described, S. luyiae sp. n., which was collected from a soil sample in a subtropical evergreen broad-leaved forest in Taiwan. An identification key to the females of Stigmatomma species with 11 antennomeres occurring in Asia is also provided.


Introduction
Stigmatomma Roger (1859) is the most diverse ant genus in the subfamily Amblyoponinae (AntCat 2017); to date, 52 extant and two fossil species are considered valid. The genus was recently revived from a synonymy with the genus Amblyopone Erichson (1842) by Yoshimura and Fisher (2012), and is currently a senior synonym of Arotropus Provancher (1881) and of Bannapone Xu (2000) (Yoshimura andFisher 2012, Ward and. Stigmatomma species are distributed in all bioregions except the neotropics. Previously, only four species had been recorded in Taiwan: S. bruni Forel (1912), S. sakaii (Terayama 1989), S. silvestrii Wheeler (1928), and S. zaojun (Terayama 2009). In Taiwan, as elsewhere, Stigmatomma species display a cryptic lifestyle, usually found in the leaf-litter, rotten wood, and in the soil of well-developed forests and forest edges (Terayama 2009). Given this, they are rarely collected.
In this paper, a new species for the genus Stigmatomma is described, S. luyiae sp. n., based on two workers collected from sifted soil, in Taiwan. In addition, an updated identification key to workers of the Asian Stigmatomma species with 11 antennomeres is presented.

Images
A Leica DFC 425 camera mounted in a Leica Z16 APO and LEICA APPLICATION SUITE software (version 3.8; Leica Microsystems, Switzerland) were used for multifocus photography. HELICON FOCUS (version 6.6.1 Pro; Helicon Soft Ltd, Ukraine) rendered the extended focus montage images.
Electron micrographs of the uncoated holotype were obtained with a Hitachi SU3500 SEM (Hitachi High-Technologies, Japan) set to high vacuum mode (SEM mode), low accelerating voltage (1.5 kV), and spot intensity 40. Specimen preparation procedures were modified from Keller (2011): the point-mounted holotype was submerged in warm water to dissolve the mounting glue before being placed in 95% ethanol for two hours. It was then attached laterally to a SEM aluminum Zeiss stub (TED PELLA, INC., USA) via a double-sided adhesive conducting PELCO tab (TED PELLA, INC., USA), and left to air dry overnight before scanning.
All images were edited and enhanced on Adobe Photoshop CS6 (version 13.0.6 x64; Adobe Systems Incorporated, USA) and are available on AntWeb.org. Illustrations were created on Adobe Illustrator CS6 (version 16.0.4; Adobe Systems Incorporated, USA)

Measurements and indices
Measurements were taken using a Leica M205C dissecting microscope (Leica Microsystems, Switzerland) with an ocular micrometer, and recorded to the nearest 0.01 mm. Abbreviations used in text are as follows:

TL
Total Length: maximum length of the specimen in lateral view, measured from the anterior-most point of the mandibles to the apex of the abdominal segment VII, excluding the sting.

HL
Head Length: length of the head in full-face view, excluding the mandibles; measured from the anterior clypeal margin to the midpoint of a transverse line connecting the posterior corners of the head.

HW
Head Width: maximum width of the head in full-face view.

HW2
Head width 2: in full-face view, width of the head immediately posterior to the posterolateral margin of the clypeus (as in Taylor 1978).

SL
Scape Length: maximum length of the scape (basal-most antennomere), excluding the basal constriction and condyle.

ML
Mandible length: outer length of the mandible (as in Taylor 1978).

WL
Weber's Length: diagonal length of the mesosoma in profile, measured from the base of the anterior slope of the pronotum to the metapleural lobe.

PPW
Propodeal posterior width: width of the propodeum in dorsal view, measured across the posterior margin of the propodeum.

PnW
Pronotal Width: maximum width of the pronotum in dorsal view.

PtW
Petiole Width: maximum width of the petiolar tergite (abdominal tergite II) in dorsal view.

PtL
Petiole Length: maximum diagonal length of the petiole in profile, measured from the anterior-most point of the subpetiolar process to the posterodorsal corner of the petiolar tergite.

Terminology
The terminology used follows prior studies: cuticular sculpture (Harris 1979), pilosity inclination (Wilson 1955), morphological terms (Keller 2011), and vestiture (Esteves and Fisher 2016). Diagnosis. Workers of Stigmatomma luyiae can be distinguished from those of other Stigmatomma species by the combination of the following characters (asterisks flag putative unique characters within Stigmatomma):
Color. Head color orange-brown; body yellow-brown; apex of gaster and appendages yellowish (Figure 1).
Etymology. The name luyiae is homage to Miss Lu-Yi Wang. The fieldwork that yielded specimens for this study could not have been completed without her participation.

Distribution.
To date, Stigmatomma luyiae sp. n. was only collected in the soil of a subtropical evergreen broad-leaved forest, which is part of the Machilus-Castanopsis vegetation zone, in Taiwan ( Figure 5).
The diagnostic characters for setting apart Stigmatomma luyiae from S. mulanae are the presence/absence of cuticular projections and modified setae on the anterior margin of the clypeus, head shape, and relative size of the mandibles. In S. luyiae, the anterior clypeal margin is flat and bears neither tubercular projections nor stout setae. Instead, stout, acuminate flattened-apex setae rise from the anterior portion of the median area of the clypeus ( Figure 2B). Also, the head is quadrate (CI: 100), and the mandibles are as long as the head (MI: 100). In S. mulanae, the anterior margin of the clypeus presents tubercle-like cuticular projections, and each of which bears a stout, conic seta ( Figure 8A); the head is rectangular (CI: 84; Xu 2000); and the mandibles are shorter than the head (ML: 0.30, HL: 0.38; Xu 2000).
Posterior margin of the head concave. Mandibular pre-apical tooth comparatively large. Anterior clypeal margin bearing eight stout, dentiform setae (