Strumigenys liui sp. nov. (Hamer, Tang & Guénard, 2025) urn:lsid:zoobank.org:act:93EF59CF-F5B6-49E0-9211–7CC64D725EF9 Fig 3A–F. Diagnosis In full-face view, head distinctly longer than wide; cephalic dorsum entirely smooth. Clypeal dorsum with short, simple, appressed setae directed anteromedially; pair of standing setae isolated to posterior margin. In lateral view, posterior margin of glandular trench clearly abutting eye. Katepistermum with long anteriorly directed free cuticular spur reaching posteroventral corner of pronotal side. Petiolar node with distinct anterior face in lateral view. Lateral margins of petiolar disc converging with anterior margin in parabolic arc in dorsal view. Postpetiolar disc in dorsal view distinctly wider than long. Basigastral costulae absent. https://doi.org/10.1371/journal.pone.0331762.t001 Material examined Physical specimen examined (n =1): Holotype worker: China; Yunnan: Hengduan Mountain, Baihua Ling; N25.302, E98.789; 1900 m a.s.l; 3 July 2019; Forest, sifted litter, C. Liu #340. MCZ-ENT00759758. ANTWEB1010117 [MCZC]. Cybertype Holotype (MCZ-ENT00759758) dataset consists of surface volume rendering image stacks of PNG files comprising full-face views stills of the head, whole body in lateral and dorsal view, as well as dorsal view of postpetiole and first gastral tergites. Further, raw CT-scan data (nii format), and a full 3D surface model (STL format) are made available. Digital stacked colour images (tif format) of the head in full-face view, and the whole body in dorsal and lateral view are also provided. All data is deposited on Zenodo (https://zenodo.org/records/14830376). A 3D surface model is also made available on Sketchfab (https://skfb.ly/pyFxD). Description Holotype worker: HW 0.35; HL 0.48; ML 0.09; SL 0.21; WL 0.52; PW 0.23; PL 0.24; PH 0.13; DPW 0.14; DPL 0.11; DPPW 0.19; DPPL 0.13; ATL 0.42; TL 1.85. Indices: CI 74.06; MI 19.25; SI 59.04; PI 64.69; LPI 55.93; DPI 58.05; DPPI 148.44. Head In full face-view, head longer than broad, broadest at posterior lobes. Posterior margin deeply concave, with thin lamellae extending across margin width; granulate cuticular structure present anteriorly to inter-posterior margin lamellae. Lateral clypeal margins converging anteriorly; anterior margin convex. Epistomal sulcus absent, cephalic dorsum and clypeus continuous; torular lobe extensive, weakly convex and obscuring antennal foramen in full-face view. Antennae totalling six segments; scape short, failing to reach posterior margin; scape weakly dorsoventrally flattened, converging anteriorly and forming distinct carinae at leading edge, narrowing basally and distally. Flagellomeres terminating in two-segment club; apicalmost segment distinctly longer than penultimate segment. Mandible triangular, reducing in width apically; basal masticatory margin with five long, triangular teeth, apical half with two shorter teeth, followed by four small teeth and apical tooth slightly larger than previous four denticles. In lateral view, preocular carina short, terminating long before eye level. Scrobe absent. Eye minute, comprised of two ommatidia. Glandular groove well impressed, extending back to eye, margins of both structures abutting. Post-buccal impression conspicuous. Ventral head margin, from preocular notch to occipital foramen, weakly sinuate being convex before eye and concave anterior to occipital foramen. In lateral view, angle of intercept between ventrolateral head margin and posterior head margin obtuse and blunt. Mesosoma In dorsal view, mesosoma lacking promesonotal suture, metanotal groove absent In lateral view, promesonotal suture weakly impressed, not reaching dorsolateral margin. Mesosomal outline weakly convex anteriorly to strongly convex posteriorly due to propodeal declivity. Dorsolateral margin rounded, lacking margination. Mesopleural notch present and well impressed. Hair wheel present. Katepistermum with long, sharp, anteriorly directed cuticular spur reaching posteroventral corner of pronotal side. Propodeal spiracle rounded, located high on propodeum. Metapleural gland bulla teardrop shape, anterodorsal corner terminating in acute angle. In dorsal view, pronotum wider than long, reaching maximum width anteriorly; lateral margins converging anteriorly with anterior margin convex. Propodeum with wide, semi-rectangular, rounded spongiform tissue. Propodeal declivity slightly concave in dorsal view. Metasoma In lateral view, petiolar peduncle short, node with distinct anterior face; dorsal nodal surface convex. Petiolar spiracle located just below node on anterolateral region of petiole. In dorsal view, petiolar disc wider than long, lateral margins converge with anterior margin in parabolic arc, posterior margin straight; postpetiolar disc wider than long, anterior margin feebly concave, lateral and posterior margins convex. In lateral view, spongiform tissue curtain present on peduncle ventrally, and on node posterodorsally. Spongiform tissue massively produced around postpetiole ventrally and laterally. First gastral tergite long, as long as petiole and postpetiole combined; in dorsal view, anterolateral corners of first gastral tergite gradually curving; anterior region of tergite with spongiform tissue. Pilosity Clypeus with short, simple, appressed setae directed anteromedially; pair of standing setae present on posterior clypeal margin, standing setae absent across remaining clypeal dorsum. Antennal segments with appressed long setae; leading margin of scape with at least two projecting setae. Mandibular dorsum with small, firmly appressed setae. Cephalic dorsum with numerous, medium length, erect, apically acute setae; few appressed longer setae also present, directed anteromedially; ventral surface of head with subdecumbent and suberect, medium length setae. In full-face view, seven long, erect simple setae located along upper scrobe margin arranged serially and directed anterolaterally. Mesosomal dorsum with scattered long, erect and decumbent setae across dorsum; fewer setae on propodeal dorsum, declivity glabrous. Pronotal humeral seta long, erect, longer than surrounding setae and directed posterolaterally. Lateral mesosomal surface almost glabrous, some setae present on pronotal dorsolateral margin zone; mesopleuron and lateral propodeal surface glabrous. Petiolar dorsum with subdecumbent, long and medium length setae, all directed posteriorly. Postpetiolar dorsum with long, erect setae. Dorsum of gastral tergite one with numerous long erect setae scattered across the surface. Gastral sternites with appressed medium length setae, and many short, erect setae. Coxa, trochanter, femur and tibia with numerous subdecumbent setae, as well as scattered long erect setae particularly on outer surface of metatibia and basitarsus. Sculpture Mandibles and antennal segments dulled by dense micropuncture. Entire body integument lacking sculpture, smooth. Basigastral costulae on first gastral tergite entirely absent. Colour Body reddish orange, appendages yellow. Spongiform tissue light yellow. Etymology Named after our colleague and friend, Dr. Cong Liu, in recognition of his ecological and taxonomic work on ants from China and other regions. Distribution Only known from Yunnan, China (Fig 1; Table 1). Comments Although only one individual was collected and described, adequate morphological evidence is provided to separate S. liui from its closest morphological relative, S. taphra. Further holotype images, and paratype specimens of S. taphra were examined and compared with images and CT-scans of S. liui. Morphological differences of particular note are the alternative pilosity on the clypeal dorsum being, short, highly appressed, instead of longer and more filamentous. Further, the absence of any basigastral costulae on the first gastral tergite, as well as the entirely smooth head dorsum (smooth and punctuate in S. taphra) further differentiates each species. The lack of additional material is not atypical for this group of Strumigenys. In the past, several species from the same group have been described from single individuals (e.g., S. daspleta, S. mnemosyne & S. runa). Thus, given the strong differing characters provided here, and the past acceptance of holotype only descriptions, it can be deemed acceptable to describe S. liui as a new species based on a single individual. As this specimen was previously identified as S. taphra, all mentions of this specimen should be revised to reflect the new taxonomy provided here. Ecology Only known from a single individual from Hengduan Mountain range in Yunnan, China. The specimen was obtained via sifted leaf litter, and like S. taphra, at high elevation (1900 m a.s.l), suggesting tolerance for higher elevation conditions.

Published as part of Hamer, Matthew T., Katzke, Julian, Tang, Kit Lam, Weemaels, André Ibáñez, Hita-Garcia, Francisco, Economo, Evan P. & Guénard, Benoit, 2025, A revision of the rare Strumigenys mnemosyne (Formicidae; Myrmicinae) group using micro-CT scanning, with the description of three new species, and the virtual repair of a broken paratype, pp. 1-29 in PLOS One 20 (9) on pages 7-11, DOI: 10.1371/journal.pone.0331762, http://zenodo.org/record/18485499