Strumigenys marmorata sp. nov. (Hamer, Tang & Guénard, 2025)

urn:lsid:zoobank.org:act:01240912–0FCD-42C9-8FC2–70FC6FB4F06E Fig 4A–F, Fig 5.

Diagnosis

In full-face view, head longer than broad. Standing setae absent on cephalic dorsum in lateral view as well as dorsolateral margin. Clypeal dorsum with short, narrowly spatulate, appressed setae, directed toward anterior clypeal margin. Basal masticatory margin with five long, triangular teeth, apical half with two shorter teeth, followed by four small teeth and apical tooth larger than previous four denticles. Scape without standing setae, appressed simple setae only. Scape dorsoventrally flattened, equal in width across length. Mesopleural notch impressed and hair wheel present. Mesosoma lacking standing setae, appressed short setae only. Meso- and metatibia lacking projecting seta. Pronotal humeral setae erect, stout and short, apically blunt. Integument lacking sculpture across body, other than basigastral costulae, coxae and basitarsi.

Material examined

Physical specimens examined (n =2):

Holotype worker; China; Hong Kong SAR, Lantau; Shek Mun Kap; 22.26906 113.93088; 22 m a.s.l; 26 November 2022; Coll. H.C. Yin; 1m² leaf litter sample; disturbed secondary forest. ANTWEB1010070 [OSFMK-P2-01] [ZRC].

1 Paratype worker; China; Hong Kong SAR, Lok Ma Chau, Fung Kung, 22.51211 114.0928; 48 m a.s.l; 18 May 2022; Coll. A.I.Weemaels & C. Neeves; 0.5 m² leaf litter sample; disturbed forest. CASENT0764984 [FK1T1W1-5] [HKBM].

The paratype specimen broke into three pieces whilst opening the specimen transportation box (Fig 5). The mesosoma remains attached to the mounting point, whilst the head and metasoma are within 75% ethanol.

Cybertype

The paratype (CASENT0764984) dataset consists of surface volume rendering image stacks of PNG files comprising isolated stills of the head in lateral view, the mandibles in anteroventral view, the metasoma and petiole in lateral view, and finally the postpetiole and gaster in lateral view. Additional surface volume renders include the whole reconstructed body in lateral and dorsal view. Further, raw volumetric data (nii format), and a full 3D surface model (STL format) are made available. Digital stacked colour images of the head in full-face view, and whole body in dorsal and lateral view are also made available of the holotype specimen (ANTWEB1010070) (TIF format), as well as the paratype specimen (CASENT0764984) (PNG format), with images of the later acquired prior to breakage. All data is deposited on Zenodo (https://zenodo.org/records/14830376). A fully reconstructed paratype (CASENT0764984) 3D surface model of the whole body is also made available on Sketchfab (https://skfb.ly/pyFxF).

Description

Holotype measurements: HW 0.34; HL 0.39; ML 0.07; SL 0.17; WL 0.40; PW 0.21; PL 0.18; PH 0.11; DPW 0.11; DPL 0.10; DPPW 0.15; DPPL 0.09; ATL 0.31; TL 1.45.

Indices: CI 87.18; MI 18.97; SI 50.59; PI 60.59; LPI 60.11; DPI 60.11; DPPI 163.44.

Paratype measurements (n =1): HW 0.39; HL 0.44; ML 0.08; SL 0.20; WL 0.46; PW 0.24; PL 0.21; PH 0.10; DPW 0.125; DPL 0.089; DPPW 0.169: DPPL 0.114; ATL 0.408; TL 1.68.

Indices: CI 89.1; MI 18.4; SI 50.6; PI 61.8; LPI 48.8; DPI 60.4; DPPI 148.25.

Head

In full face-view, head longer than broad, broadest anterior to posterior margin. Posterior margin broadly concave. Lateral clypeal margins converging anteriorly; anterior margin straight to subtly convex. Epistomal sulcus absent, cephalic dorsum and clypeus continuous; torular lobe small, convex and obscuring antennal foramen in full-face view. Antennae totalling six segments; scape short, failing to reach posterior margin; scape dorsoventrally flattened, converging anteriorly and forming flange at leading edge, narrowing basally and distally. Flagellomeres terminating in two-segmented club; apicalmost segment 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 larger than previous four denticles.

In lateral view, preocular carina short, terminating long before eye. Scape not well impressed; integument smooth. Eye minute, comprised of single ommatidium. Postbuccal impression conspicuous; ventral head margin, from preocular notch to occipital foramen, significantly sinuate being convex before eye then concave anterior to occipital foramen. In lateral view, angle of intercept between ventrolateral head margin and posterior head margin obtuse, with posterior projecting cuticular lobe at intercept.

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 almost reaching posteroventral corner of the pronotal side. In dorsal view, pronotum evenly rounded anteriorly, reaching maximum width at mid-length. Propodeum unarmed; propodeum with semi-rectangular, dorsally rounded spongiform tissue only. Propodeal declivity slightly concave in dorsal view.

Metasoma

In lateral view, petiole clavate; petiolar node slightly longer than wide; peduncle and anterior petiolar face meeting at conspicuous obtuse angle; anterior face of petiole flat, grading into dorsal face with curved angle. Dorsal margin of petiole and postpetiole surface convex. In dorsal view, petiole oval, wider than long. In dorsal view, postpetiole reniform, anterior margin conspicuously concave, lateral margins converging in parabolic arc posteriorly, posterior margin with concave notch medially. Ventral petiolar spongiform tissue present as short curtain; lateral petiolar spongiform tissue comparatively small. Conspicuous ventral and lateral spongiform tissue on postpetiole, obscuring lateral surface. Spongiform tissue surrounding postpetiolar disc anteriorly and posteriorly in dorsal view, but not on top of postpetiolar disc itself.

Pilosity

In lateral view, cephalic dorsum and dorsolateral margins lacking standing setae. Setae on cephalic dorsum in full-face view short and appressed. Spatulate setae concentrated anteriorly on cephalic dorsum, directed inwards to cephalic mid-line. Simple setae concentrated on posterior cephalic dorsum, extending over posterior lobes and onto lateral cephalic surface. Dorsum of clypeus lacking standing setae, setae instead narrowly spatulate, appressed and directed anteriorly. Setae on both cephalic and clypeal dorsa well-spaced. Ventral cephalic setae mix of short, appressed setae alongside long, appressed simple setae. Postbuccal cavity with conspicuous series of long and erect simple setae noticeably longer than surrounding setae on cephalic dorsum. Scape lacking standing setae, appressed, simple setae only. Flagellomere segments with short, appressed simple setae, reaching highest concentration on apical segment. Pronotal humeral seta conspicuous, simple and apically blunt, directed antero-laterally and well differentiated from surrounding mesosomal setae. Dorsal mesosomal setae appressed and simple, directed inwards to mesosomal longitudinal midline. Hair wheel with three to five, appressed simple setae. Petiole and postpetiole disc with same seta type, but directed in random directions. Disc of postpetiole also with erect simple setae, with one pair located on the posterior margin, directed posterodorsally. Gastral tergites with both stout erect setae and short appressed setae. Gastral sternites in lateral view, with long, erect simple setae, noticeably shorter and less stout than those on gastral dorsum. Gastral sternites also with long, appressed to semi-erect simple setae. Dorsal (outer) surfaces of meso- and meta-basitarsi and tibiae lacking long projecting setae; short, decumbent setae on tibiae and tarsal segments only; setae directed towards respective segment apex.

Colour

Body colour reddish brown, appendages light reddish brown, spongiform tissue light yellow.

Sculpture

Almost entire body integument lacking sculpture, the only sculpture located on first gastral tergite in the form of basigastral costulae, and micro-punctures on antennae, coxae and basitarsi. Integument reflecting under non-diffused light.

Etymology

From Latin marmorāta f (“marbled, covered or encrusted with marble”), nominative feminine singular of marmorātus. Named for the highly smooth integument surface across the body which resembles marble, a highly smooth, shiny rock when cut and polished.

Distribution

Only known from Hong Kong, China (Fig 1; Table 1).

Comments

Strumigenys marmorata sp. nov is a member of the S. mnemosyne group sharing all characters of the species group [3]. However, interesting morphological differences are apparent between S. marmorata and other members of the species group. These include seta differences on scape, and a lack of setae across the body. These characters have been integrated into the species group definition.

Within the S. mnemosyne group, S. marmorata most closely resembles S. mnemosyne and S. rimdahli due to the lack of standing setae on the scape. Strumigenys marmorata can be differentiated from S. mnemosyne by the lack of standing setae on the cephalic, mesosomal and petiole dorsum. Abrasion is unlikely here due to the lack of setae bearing points embedded within the integument of S. marmorata. Clypeal setae in S. marmorata are similarly arranged as in S. mnemosyne but are narrowly spatulate in S. marmorata. The scape in S. mnemosyne is constricted proximally but in S. marmorata the scape is as wide proximally as apically. The head width of S. marmorata is distinctly wider than in S. mnemosyne (0.39 and 0.30 mm respectively), and in fact is the widest in the species group, even wider than S. taphra (HW 0.35–0.37mm), the largest member of the S. mnemosyne group (TL 1.9–2.0). Strumigenys mnemosyne was collected by Bolton in Sarawak (Malaysia), and is known from other localities all restricted to Borneo Island,>1650 km from the collection locality in Hong Kong. Given the large geographic distance and unique morphological characters, misidentification between S. marmorata and S. mnemosyne is unlikely. Interestingly, the smooth and shining cuticular surface (including the femora and tibia) is a rare characteristic within Strumigenys species [7]. Strumigenys marmorata is also morphologically similar to S. rimdahli, however both can be readily separated by the presence of a sharp dorsolateral mesosomal margin in S. rimdahli (rounded in S. marmorata), and a convex rather than flat mesosomal dorsum in S. marmorata.

Ecology

Strumigenys marmorata is known from two individuals collected within two distinct leaf litter samples from lowland areas in Hong Kong. At the paratype collection locality, an additional 24 leaf-litter samples were carried out to obtain additional individuals, but none were collected unfortunately, suggesting the rarity of this species. Interestingly, both holotype and paratype collection localities had numerous tramp and exotic ant species, including several Strumigenys species such as, Strumigenys emmae (Emery, 1890), S. membranifera Emery, 1869 and S. nepalensis De Andrade, 1994. Other tramp and exotic ant species included, Tetramorium lanuginosum Mayr, 1870, Brachyponera obscurans (Walker, 1859), Pheidole megacephala (Fabricius, 1793) and Ooceraea biroi (Forel, 1907) were collected at each site. Collection sites were far from pristine, with surface leaf litter light, heavily composed of loose soil and general anthropogenic detritus.