Proceratium bruelheidei

Most of the type series was collected during a leaf litter ant survey (Noack 2016) in the experimental tree plantations of the BEF-China Main Experiment (Bruelheide et al. 2014). No direct observations of biology and natural history are available. The trees under which the Winkler samples yielding seven of eight type specimens were collected were just six years old and had a mean diameter at breast height of 5.6 ± 2.5 cm (n=7) (Noack 2016). This may indicate that P. bruelheidei could prefer early successional forests with a relatively open soil, as the ground from which leaf litter was taken had a mean litter cover of 55 ± 24% (n=7). The single specimen (CASENT0790027) from the Gutianshan National Nature Reserve was likewise collected from an early successional forest stand that was clear-cut less than 20 years prior to the collection of the specimen. However, further sampling will be necessary to draw quantitative conclusions on habitat preferences.

Identification
A member of the Proceratium itoi clade. Links to data, images and a 3D model of this species are noted (and linked to) in the Type Material section below.

Proceratium bruelheidei differs from the other members of the P. itoi clade by the following character combination: relatively large species (TL 3.61–4.00); sides of head straight to very weakly convex, posterior sides only narrowing dorsally, vertex convex; frontal carinae well developed, with large lamellae that extend laterally above the antennal insertions; frontal furrow inconspicuous and of the same color as the surrounding anterior cephalic dorsum; posterodorsal corners of the propodeum broadly angular; propodeal declivity superficially punctured, but shiny; posterior face of petiolar node in profile as steep as anterior face and less than half as long as anterior face; apex of the petiolar node almost as long as broad in dorsal view; subpetiolar process roughly trapezoid and well developed (albeit with variable ventral outline); abdominal segment IV very strongly recurved (IGR 0.24–0.26); in addition to dense pubescence, abundant erect hairs present on scapes and dorsal surface of body, longest of those hairs longer than maximum dorsoventral diameter of metafemur.

Proceratium bruelheidei is most similar to Proceratium kepingmai. From the other species of the Proceratium itoi clade, Proceratium bruelheidei can be separated by using the characters given in the ‘taxonomic notes’ of Proceratium kepingmai below. From this species, Proceratium bruelheidei differs by the shape of the head in full-face view with straight sides and a convex vertex (sides convex, broadest at level of eyes and vertex almost straight in Proceratium kepingmai), the shiny propodeal declivity that is only superficially punctured (densely punctured and mostly opaque in Proceratium kepingmai), the inconspicuous frontal furrow that has the same color as the surrounding anterior cephalic dorsum (frontal furrow conspicuous and dark in Proceratium kepingmai), the posterior face of petiolar node as steep as the anterior face of the node and less than half as long as the anterior face (posterior face steeper than anterior face and about half as long in Proceratium kepingmai), the apex of the petiolar node that is little broader than long (clearly broader than long in Proceratium kepingmai), and the more strongly recurved abdominal segment IV (IGR 0.24–0.26) (IGR 0.30–0.32 in Proceratium kepingmai). Additionally, Proceratium bruelheidei has distinctly more and longer erect hairs protruding from the dense pubescence on the dorsum of the body and the ventral abdomen. While the number of hairs may be a treacherous character as hairs can break during specimen processing, the length of hairs can reliably be quantified. In Proceratium bruelheidei the longest erect hairs on the dorsum of the petiole and on abdominal sternum III are longer than the maximum dorsoventral diameter of the metafemur (as long as or shorter than maximum diameter of metafemur in Proceratium kepingmai).

Variation. The variation in body size is within the normal limits of other Proceratium species and the type specimens of Proceratium bruelheidei show, with the notable exception of the subpetiolar process, no observable intraspecific differences. While the process is well developed and roughly trapezoid in all available specimens, its size, exact shape, and ventral outline vary. In the holotype (CASENT0790023) and several paratypes (CASENT0790025, CASENT0790026, CASENT0790029) the subpetiolar process has a distinct notch, so that it almost looks like an upside-down volcano. This notch is absent in other specimens (CASENT0790027, CASENT0790028, CASENT0790030), where the ventral outline of the process is straight. In one specimen (CASENT0790024) the ventral outline is also straight but with a row of minute denticles. It thus appears that this character, which is often used to delimitate Proceratium species (e.g. Baroni Urbani and de Andrade 2003, Hita Garcia et al. 2014), may be less suitable for species in the Proceratium itoi clade, as also indicated by the variation in the subpetiolar process within the type series of Proceratium zhaoi.

Distribution based on Regional Taxon Lists
Palaearctic Region: China.

Nomenclature

 *  bruelheidei. Proceratium bruelheidei Staab, Xu & Hita Garcia, 2018: 148, figs. 4B, 6B, 7B, 7D, 8, 9, 24 (w.) CHINA.

Worker
Holotype: TL 3.94; EL 0.04; SL 0.50; HL 0.84; HLM 1.09; HW 0.79; WL 1.06; MFeL 0.69; MTiL 0.54; MBaL 0.40; PeL 0.39; PeW 0.32; LT3 0.56; LS4 0.21; LT4 0.84; OI 4; CI 93; SI 59; MFeI 87; MTiI 69; MBaI 51; DPeI 81; IGR 0.25; ASI 150. Paratypes: (n = 7). TL 3.61–4.00; EL 0.03–0.04; SL 0.49–0.53; HL 0.79–0.86; HLM 0.96–1.08; HW 0.73–0.79; WL 1.03–1.10; MFeL 0.63–0.74; MTiL 0.54– 0.58; MBaL 0.39–0.41; PeL 0.36–0.39; PeW 0.30–0.32; LT3 0.51–0.58; LS4 0.19– 0.22; LT4 0.75–0.92; OI 4–5; CI 89–94; SI 60–63; MFeI 86–96; MTiI 69–74; MBaI 50–54; DPeI 82–84; IGR 0.24–0.26; ASI 145–159.

In full-face view, head slightly longer than broad (CI 89– 94), anterior sides straight to very weakly convex, posterior sides narrowing dorsally, vertex convex. Clypeus reduced and narrow, with a broadly triangular median anterior projection. Frontal carinae relatively short, moderately separated, slightly covering antennal insertions, constantly diverging posteriorly, lateral expansions of anterior part of frontal carinae developed as broad lamellae, raised, conspicuously and broadly extending laterally above antennal insertions; frontal area convex; frontal furrow developed as a raised carina, starting at the clypeal projection and extending over the anterior 2/5 of the cephalic dorsum, with a short gap at the level where the lamellae of frontal carinae are broadest, frontal furrow less conspicuous after the gap. Eyes reduced, minute (OI 4–5), consisting of one to four ommatidia and located on midline of head. Antennae 12-segmented, scapes short (SI 59–63), not reaching posterior head margin and thickening apically. Mandibles elongate and triangular, relatively slender, masticatory margin with four teeth in total, apical tooth long and acute, the other teeth smaller and decreasing in size from second to fourth tooth, gap between second and third tooth larger than between other teeth.

Mesosoma in profile slightly convex and as long as maximum head length including mandibles (WL 1.03–1.10 vs HLM 0.96–1.09). Lower mesopleurae (katepisterna) with well-demarcated sutures, upper mesopleurae (anepisterna) with inconspicuous sutures, no other sutures developed on lateral and dorsal mesosoma; lower mesopleurae weakly inflated posteriorly; posterodorsal corner of propodeum broadly angular, propodeal lobes weakly developed as bluntly rounded lamellae; propodeal declivity almost vertical, slightly inclined anteriorly; in posterodorsal view, sides of propodeum separated from declivity by distinct lamellate margins; in profile view, propodeal spiracle rounded, at mid height, opening of spiracle slightly facing posteriorly. Legs moderately long (MFeL 0.63–0.74, MTiL 0.54–0.58, MBaL 0.39–0.41); all tibiae with a pectinate spur; calcar of strigil without a basal spine; pretarsal claws simple; arolia present.

Petiolar node in profile high, nodiform, with a straight and sloping anterior face, dorsum of node broadly rounded, posterior face as steep as anterior face and relatively short, less than half as long as anterior face; petiole in dorsal view longer than broad, apex of node almost as long as broad; ventral process of petiole well developed, with a roughly trapezoid projection of varying shape and ventral outline (see ‘variation’). In dorsal view abdominal segment III anteriorly much broader than petiole; its sides convex; abdominal sternite III anteriomedially with a conspicuous depression marked by a thin rim. Constriction between abdominal segments III and IV deep. Abdominal segment IV very large, strongly recurved (IGR 0.24–0.26) and posteriorly rounded, with a lamella on its anterior border around the constriction to abdominal segment III, this lamella thicker ventrally than dorsally; abdominal tergum IV 1.5– 1.6X longer than abdominal tergum III (ASI 145–159), remaining abdominal tergites and sternites inconspicuous and projecting anteriorly. Sting large and extended.

Whole body covered with dense mat of short, decumbent to suberect pubescent hairs; additionally, dorsal surfaces of body with abundant significantly longer suberect and erect hairs; such hairs also present on abdominal sterna III + IV, scapes (anterior faces of scapes with many hairs, posterior faces with fewer hairs) and legs (ventral faces of femora and tibiae with many hairs, dorsal faces with fewer hairs), the longest hairs on dorsal surface of body longer than the maximum dorsoventral diameter of metafemur. Mandibles striate; entire body densely punctate; on sides of pronotum punctures aligned in diffuse lines, appearing striate; punctures on antennae, legs, and abdominal segment IV finer than on rest of body; propodeal declivity shiny and at most superficially punctate; abdominal segments V–VII very superficially reticulate and shiny. Body color uniformly orange brown to reddish brown, vertex of head slightly darker, legs, antennal funiculus, and abdominal segments V– VII yellowish brown.

Type Material
Holotype: Pinned worker from CHINA, Jiangxi Province, near the village Xingangshan, ca. 15 km SE of Wuyuan, 29°7'24"N / 117°54'25"E, 158 m asl, early successional tree plantation of the BEF-China experiment, Winkler leaf litter extraction, 26-IV-2015, leg. Merle Noack, label “MN290” (CASENT0790023), deposited in.

Paratypes: Seven pinned workers in total; one with same data as holotype except label “MN291” (CASENT0790025, in SWFU); one with same data as holotype except 29°7'24"N / 117°54'31"E, 204 m asl, 22-IV-2015, label “MN248” (CASENT0790024, in SWFU); one with same data as holotype except 29°7'33"N / 117°54'41"E, 246 m asl, 30-IV-2015, label “MN309” (CASENT0790029, in SWFU); one with same data as holotype except 29°7'33"N / 117°54'40"E, 239 m asl, 04-V-2015, label “MN371” (CASENT0790030, in SWFU); one with same data as holotype except 29°7'15"N / 117°54'22"E, 122 m asl, 12-V-2015, label “MN479” (CASENT0790028, in ); one with same data as holotype except 29°7'37"N / 117°54'25"E, 219 m asl, 20-V-2015, label “MN525” (CASENT0790026, in  ); one from CHINA, Zhejiang Province, Gutianshan National Nature Reserve, ca. 35 km NW of Kaihua, 29°16'37"N / 118°5'26"E, 617 m asl, young secondary subtropical mixed forest, manual sifting of leaf litter, 11-VII-2008, leg. Andreas Schuldt, label “CSP 22” (CASENT0790027, in ZMHB).

Cybertype. Volumetric raw data (in DICOM format), a 3D rotation video (in .mp4 format, see Suppl. material 3: Video 1), still images of surface volume rendering, a 3D surface (in PLY format), and montage photos illustrating the head, profile and dorsal views of the body of the physical holotype (CASENT0790023) were all generated as part of this study. Data and images are freely available for download from a Dryad repository (there is a download link at the top right of the webpage) and a 3D surface model of the holotype can be viewed online at Sketchfab.

Etymology
The species epithet is a patronym in honor of the German botanist Prof. Helge Bruelheide and his efforts in establishing and promoting the BEF-China project. All specimens of this species were collected on BEF-China field sites.