Systematics of the ant genus Proceratium Roger (Hymenoptera, Formicidae, Proceratiinae) in China – with descriptions of three new species based on micro-CT enhanced next-generation-morphology

Michael Staab; Francisco Hita Garcia; Cong Liu; Zheng-Hui Xu; Evan P. Economo

doi:10.3897/zookeys.770.24908

Research Article

Systematics of the ant genus Proceratium Roger (Hymenoptera, Formicidae, Proceratiinae) in China – with descriptions of three new species based on micro-CT enhanced next-generation-morphology

Michael Staab^‡, Francisco Hita Garcia^§, Cong Liu^§, Zheng-Hui Xu^|, Evan P. Economo^§

‡ University of Freiburg, Freiburg, Germany

§ Okinawa Institute of Science and Technology Graduate University, Onna-son, Japan

| Southwest Forestry University, Kunming, China

Corresponding author: Michael Staab ( michael.staab1@tu-darmstadt.de )

Academic editor: Marek Borowiec

This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Citation: Staab M, Hita Garcia F, Liu C, Xu Z-H, Economo EP (2018) Systematics of the ant genus Proceratium Roger (Hymenoptera, Formicidae, Proceratiinae) in China – with descriptions of three new species based on micro-CT enhanced next-generation-morphology. ZooKeys 770: 137-192. https://doi.org/10.3897/zookeys.770.24908

ZooBank: urn:lsid:zoobank.org:pub:63FDA225-900E-42A6-9FD1-8B02D8CD1F44

Abstract

The genus Proceratium Roger, 1863 contains cryptic, subterranean ants that are seldom sampled and rare in natural history collections. Furthermore, most Proceratium specimens are extremely hairy and, due to their enlarged and curved gaster, often mounted suboptimally. As a consequence, the poorly observable physical characteristics of the material and its scarcity result in a rather challenging alpha taxonomy of this group. In this study, the taxonomy of the Chinese Proceratium fauna is reviewed and updated by combining examinations of traditional light microscopy with x-ray microtomography (micro-CT). Based on micro-CT scans of seven out of eight species, virtual 3D surface models were generated that permit in-depth comparative analyses of specimen morphology in order to overcome the difficulties to examine physical material of Proceratium. Eight Chinese species are recognized, of which three are newly described: Proceratium bruelheidei Staab, Xu & Hita Garcia, sp. n. and P. kepingmai sp. n. belong to the P. itoi clade and have been collected in the subtropical forests of southeast China, whereas P. shohei sp. n. belongs to the P. stictum clade and it is only known from a tropical forest of Yunnan Province. Proceratium nujiangense Xu, 2006 syn. n. is proposed as a junior synonym of P. zhaoi Xu, 2000. These taxonomic acts raise the number of known Chinese Proceratium species to eight. In order to integrate the new species into the existing taxonomic system and to facilitate identifications, an illustrated key to the worker caste of all Chinese species is provided, supplemented by species accounts with high-resolution montage images and still images of volume renderings of 3D models based on micro-CT. Moreover, cybertype datasets are provided for the new species, as well as digital datasets for the remaining species that include the raw micro-CT scan data, 3D surface models, 3D rotation videos, and all light photography and micro-CT still images. These datasets are available online (Dryad, Staab et al. 2018, http://dx.doi.org/10.5061/dryad.h6j0g4p).

Keywords

3D model, BEF-China, cybertype, Gutianshan National Nature Reserve, subtropical forest, taxonomy, tropical forest, Xishuangbanna

Introduction

Recent phylogenetic studies have clarified the evolutionary history of ant subfamilies and genera. One higher-level taxon consistently recovered is the subfamily Proceratiinae, which belongs to the poneroid clade (e.g. Brady et al. 2006, Moreau et al. 2006, Blanchard and Moreau 2017, Borowiec et al. 2017). This subfamily currently contains three valid extant genera and one fossil genus with eight fossil and 144 valid extant species, and one fossil genus with four species (Bolton 2018). Proceratium Roger, 1863 is the largest genus in the subfamily with 83 extant and six fossil species. However, based on recent molecular phylogenetic results, the monophyly of the genus appears doubtful (Borowiec et al. 2017). While globally distributed, with the majority of species occurring in warm and sufficiently wet climates, the geographic record is very patchy (Baroni Urbani and de Andrade 2003, Hita Garcia et al. 2014, Guénard et al. 2017). Specimens are only rarely collected, usually in leaf litter or soil samples. Colonies typically occur in low densities (but see Masuko 2010) and are small, having usually fewer than 100 workers (but see Onoyama and Yoshimura 2002, Fisher 2005). Proceratium have a cryptobiotic lifestyle with hypogeic foraging habits and nesting in leaf litter, rotting wood, top soil, or below stones (Baroni Urbani and de Andrade 2003). As far as it is known, they are specialized predators of the eggs of spiders and other arthropods, which can be stored in large quantities in the nest (e.g. Brown 1957, Brown 1979, Fisher 2005). Notably, some Japanese Proceratium species also display larval haemolymph feeding, a behavior otherwise only known from the ‘dracula ant’ subfamily Amblyoponinae (Masuko 1986). However, if this is a typical feature for the whole genus or restricted to a few congeners remains unknown and requires more in-depth natural history data than currently available.

The genus has been comprehensively revised on a global scale by Baroni Urbani and de Andrade (2003). The authors also refined the internal species clades originally erected by Brown (1958) and grouped the genus in eight internal clades that reflect the relationships of a morphology-based phylogeny (Baroni Urbani and de Andrade 2003). Nevertheless, the account on the genus is far from complete, as can be seen in the few single species descriptions (Fisher 2005, Liu et al. 2015a) and regional revisions published since then (Xu 2006, Hita Garcia et al. 2014, 2015). Considering the cryptic lifestyle and extreme rarity in collections, it is very likely that many more species await discovery and formal taxonomic treatment. In China, seven Proceratium species from three clades (P. itoi clade, P. silaceum clade, P. stictum clade) have been recorded so far (Xu 2000, Xu 2006, Liu et al. 2015b), albeit the geographic coverage within the country is poor (Guénard and Dunn 2012). The genus is only known from the provinces of Yunnan (six species), Hunan (two species), Zhejiang (one species), and the island of Taiwan (two species). There are no records from the other provinces in south and southeast China where Proceratium populations almost inevitably occur.

In the last decade, X-ray microtomography (micro-CT) technology has gained popularity among systematicists and is being increasingly employed in arthropod taxonomy. Micro-CT is a state-of-the-art imaging technology that facilitates the generation of high-resolution, virtual, and interactive three-dimensional (3D) reconstructions of whole specimens or of particular body parts (Hörnschemeyer et al. 2002, Friedrich and Beutel 2008). The virtual nature of such reconstructions enables non-destructive and comprehensive 3D analyses of anatomy and morphology (Faulwetter et al. 2013, Friedrich et al. 2014). Another crucial benefit of micro-CT is its application for virtual dissections and identification of new diagnostic characters (Deans et al. 2012), which has been successfully applied for lepidopterans (Simonsen and Kitching 2014), mayflies (Sartori et al. 2016), and recently ants (Hita Garcia et al. 2017a).

Despite its common usage in invertebrate paleontology, as well as functional and comparative morphology (e.g. Beutel et al. 2008, Berry and Ibbotson 2010, Barden and Grimaldi 2012), until very recently micro-CT was not applied to alpha taxonomy. In the last years, this situation is changing and micro-CT has become a powerful tool to visually enhance and support diagnostic species delimitations, from single species descriptions to revisions. While initially used for polychaetes (Faulwetter et al. 2013), myriapods (Stoev et al. 2013, Akkari et al. 2015), spiders (Michalik and Ramírez 2013), earthworms (Fernández et al. 2014), and flatworms (Carbayo and Lenihan 2016, Carbayo et al. 2016), micro-CT has evolved into a cutting-edge tool increasingly applied for ant taxonomy (Csősz 2012, Fischer et al. 2016, Sarnat et al. 2016, Agavekar et al 2017, Hita Garcia et al. 2017a, 2017b). A detailed and critical assessment of the technology and its applications for ant taxonomy was provided by Hita Garcia et al. (2017b). Another key advantage of applying micro-CT for invertebrate taxonomy is the use of openly available cybertype datasets linked to the original, physical type material (Faulwetter et al. 2013, Akkari et al. 2015, Hita Garcia et al. 2017b).

In this study, we provide a review of the genus Proceratium in China, in which we describe three new species: P. bruelheidei sp. n. and P. kepingmai sp. n. from the P. itoi clade from subtropical southeast China and P. shohei sp. n. from the P. stictum clade from the tropical south of Yunnan Province. The newly available insights from this study suggest that P. nujiangense Xu, 2006 is conspecific with P. zhaoi Xu, 2000. Thus, we treat P. nujiangense syn. n. as a junior synonym of P. zhaoi. To distinguish the new species from morphologically similar species, particularly in the P. itoi clade, and to ease future identifications, we provide an illustrated key to the Chinese fauna. We also give species accounts for all other valid species and add a locality record for Proceratium longigaster Karavaiev, 1935. Like in previous studies (Fischer et al. 2016, Sarnat et al. 2016, Agavekar et al. 2017, Hita Garcia et al. 2017a, 2017b), we continue using and exploring microtomography for ant taxonomy. In order to visually enhance the taxonomic descriptions, we provide still images and 3D videos based on surface volume renderings of micro-CT scans from all Chinese species (except for P. longmenense Xu, 2006). Since the treated species are rather hairy, often dirty, and too scarce for any physical specimen manipulations, we also use the 3D reconstructions for virtual in-depth examinations of surface morphology. Furthermore, the complete micro-CT datasets containing the scan raw data, 3D rotation videos, still images of 3D models, and 3D surfaces supplemented by color montage photos are made freely available online (Staab et al. 2018, http://dx.doi.org/10.5061/dryad.h6j0g4p) as cybertypes.

Materials and methods

Abbreviations of depositories

The collection abbreviations follow Evenhuis (2018). The material upon which this study is based is located or will be deposited at the following institutions:

BMNH The Natural History Museum, London, UK

CASC California Academy of Sciences, San Francisco, California, USA

MHNG Muséum d’Histoire Naturelle de la Ville de Genève, Geneva, Switzerland

NIAES National Institute for Agro-Environmental Sciences, Japan

NHMB Naturhistorisches Museum Basel, Switzerland

OIST Okinawa Institute of Science and Technology, Onna-son, Japan

SIZK Schmalhausen Institute of Zoology, Kiev, Ukraine

SWFU Southwest Forestry University, Kunming, Yunnan, PR China

TARI Taiwan Agricultural Research Institute, Taichung, Taiwan

ZMBH Museum für Naturkunde der Humboldt-Universität, Berlin, Germany

Specimens and imaging

The material of the new species was collected during recent ecological field work activities of the first author (see e.g. Staab et al. 2014, Staab et al. 2017) and others (see Liu et al. 2016). All available worker specimens were mounted and measured with a Leica M125 stereo microscope under magnification of 80–100×. To compose montage images, we took raw image stacks with a Leica M205C microscope equipped with a Leica DFC450 camera and then assembled montage images with Helicon Focus (version 6) software. Additional material of previously described Proceratium species known to occur in China and of Asian species from the three Proceratium species clades containing Chinese species (P. itoi clade, P. silaceum clade, P. stictum clade) was also examined (see species and specimen data in Suppl. material 1: Table S1 for non-Chinese species). The other distributional data used for map generation was extracted from Antmaps.org (Janicki et al. 2016, Guénard et al. 2017).

Measurements and indices

The following measurements (all expressed in mm) and indices are based on Hita Garcia et al. (2014, 2015):

EL Eye length: maximum length of eye measured in oblique lateral view.

HL Head length: maximum measurable distance from the mid-point of the anterior clypeal margin to the mid-point of the posterior margin of head, measured in full-face view. Impressions on anterior clypeal margin and posterior head margin reduce head length.

HLM Head length with mandibles: maximum head length in full-face view including closed mandibles.

HW Head width: maximum head width directly above the eyes, measured in full-face view.

MFeL Metafemur length: maximum length of metafemur measured along its external face.

MTiL Metatibia length: maximum length of metatibia measured along its external face.

MBaL Metabasitarsus length: maximum length of metabasitarsus measured along its external face.

LT3 Abdominal tergum III length: maximum length of abdominal tergum III (=length of abdominal segment III) in lateral view.

LS4 Abdominal sternum IV length: maximum length of abdominal sternum IV in lateral view.

LT4 Abdominal tergum IV length: maximum length of abdominal tergum IV in lateral view.

PeL Petiolar length: maximum length of the petiolar node in dorsal view including its anterior prolongation.

PeW Petiolar width: maximum width of petiole measured in dorsal view.

SL Scape length: maximum length of scape shaft excluding basal condyle.

TL Total body length: combined length of HLM + WL + PeL + LT3 + LT4.

WL Weber’s length: diagonal length of mesosoma in lateral view from the anterior-most point of pronotal slope (excluding neck) to posteroventral margin of propodeal lamella or lobe.

CI Cephalic index: HW / HL * 100

OI Ocular index: EL / HW * 100

SI Scape index: SL / HL * 100

MFeI Metafemur length index: MFeL / HW * 100

MTiI Metatibia length index: MTiL / HW * 100

MBaI Metabasitarsus length index: MBaL / HW * 100

DPeI Dorsal petiole index: PeW / PeL * 100

ASI Abdominal segment index: LT4 /LT3 * 100

IGR Gastral reflexion index: LS4 / LT4

X-ray micro computed tomography and 3D images

We scanned all Chinese Proceratium species, except for P. longmenense from which no material was available for micro-CT analysis. For each of the new species, we scanned the holotype worker specimen, whereas for the remainder of the species we either scanned a paratype or non-type specimen, if no type material was available. An overview of scanning parameters and specimens used is provided in Table 1. All micro-CT scans were performed using a Zeiss Xradia 510 Versa 3D X-ray microscope operated with the Zeiss Scout-and-Scan Control System software (version 11.1.6411.17883). 3D reconstructions of the resulting scan raw data were done with the Zeiss Scout-and-Scan Control System Reconstructor (version 11.1.6411.17883) and saved in DICOM file format. Volume renderings, surface mesh generations, virtual examinations and dissections were performed with Amira software (version 6.3.0). Post-processing of mesh data in order to generate clean surfaces was done with Meshlab (version 1.3.3). The methodology for the virtual examinations of 3D surface models, generation of 3D rotation videos, and virtual dissections follow Hita Garcia et al. (2017a). For more details on micro-CT scanning and post-processing workflow pipeline, we refer to the exhaustive descriptions in Hita Garcia et al. (2017a, 2017b).

Table 1.

Download as

CSV

XLSX

Overview of micro-CT scanning data presenting specimen data, scan settings, and voxel sizes for the resulting scans (all specimens are workers and all files are in DICOM format).

Species	Identifier	Type status	Magnification (x)	Exposure (s)	Voxel size (µm)	Source distance (mm)	Detector distance (mm)	Voltage (kV)	Power (W)	Amperage (µA)
deelemani	CASENT0790842	non-type	4	1.5	4.826	24.99	10	45.24	3.54	78.14
kepingmai	CASENT0790031	holotype	4	1.5	4.359	19.99	11	45.23	3.54	78.3
bruelheidei	CASENT0790023	holotype	4	1.5	4.359	19.99	11	45.24	3.55	78.35
itoi	OKENT0016142	non-type	4	0.8	3.660	13	11	45.24	3.54	78.29
japonicum	CASENT0790834	non-type	4	0.8	3.897	14.99	11	45.24	3.54	78.17
longigaster	CASENT0790673	non-type	4	0.8	3.097	11	13	45.24	3.54	78.19
nujiangense	CASENT0790672	paratype	4	1.5	2.534	12	19.99	45.24	3.54	78.19
shohei	CASENT0717686	holotype	4	1.5	4.193	17.99	11	45.24	3.53	78.05
zhaoi	CASENT0790671	paratype	4	1.5	2.252	11	22	45.24	3.54	78.33

Data availability

All specimens used in this study have been databased and the data are freely accessible on AntWeb (http://www.antweb.org). Each specimen can be traced by a unique specimen identifier attached to its pin. The Cybertype datasets provided in this study consist of the full micro-CT original volumetric datasets (in DICOM format), 3D surface models (in STL and PLY formats), 3D rotation video files (in .mp4 format, see Suppl. material), all light photography montage images, and all image plates including all important images of 3D models for each species. All data have been archived and are freely available from the Dryad Digital Repository (Staab et al. 2018, http://dx.doi.org/10.5061/dryad.h6j0g4p). In addition to the cybertype data at Dryad, we also provide freely accessible 3D surface models of all treated species on Sketchfab (https://sketchfab.com/arilab/collections/proceratium).

Results

Synopsis of Chinese Proceratium species

Proceratium itoi clade

Proceratium bruelheidei Staab, Xu & Hita Garcia sp. n. [China: Jiangxi, Zhejiang]

Proceratium itoi (Forel, 1918) [China: Hunan, Zhejiang; Taiwan; Japan; South Korea; Vietnam]

Proceratium kepingmai Staab, Xu & Hita Garcia sp. n. [China: Jiangxi, Zhejiang]

Proceratium longmenense Xu, 2006 [China: Yunnan]

Proceratium zhaoi Xu, 2000 [China: Yunnan]

= Proceratium nujiangense Xu, 2006 [China: Yunnan] syn. n.

Proceratium silaceum clade

Proceratium japonicum Santschi, 1937 [China: Yunnan; Taiwan; Japan]

= Proceratium formosicola Terayama, 1985 [Taiwan]

Proceratium longigaster Karavaiev, 1935 [China: Hunan, Yunnan, Zhejiang; Vietnam]

Proceratium stictum clade

Proceratium shohei Staab, Xu & Hita Garcia sp. n. [China: Yunnan]

Identification key to Chinese Proceratium species (workers)

This key is partly derived from Baroni Urbani and de Andrade (2003) and Xu (2006).

1	In profile, petiolar node squamiform and rectangular, high and erect (Fig. 1A)	2
–	In profile, petiolar node never squamiform, either low, elongate, and barrel-shaped, or rounded-triangular (Fig. 1B)	3
2	In profile, petiolar node clearly narrowing dorsally, broader on the base than on the apex (Fig. 2A); in dorsal view, petiole at least 1.5× wider than long (DPeI ≥155); abundant long appressed shaggy hairs from LT3 project distinctly over the constriction between LT3 and LT4 (Fig. 2A) [China: Hunan, Yunnan, Zhejiang; Vietnam]	*P. longigaster*
–	In profile, petiolar node not or only weakly narrowing dorsally, the base as or almost as broad as the apex (Fig. 2B); even if narrowing, petiole never 1.5× times wider than long in dorsal view (DPeI <150); no shaggy hairs protruding from LT3 over the constriction to LT4, if single longer hairs present, then not shaggy (Fig. 2B) [China: Yunnan; Taiwan; Japan]	*P. japonicum*
3	Anterior clypeal margin with a distinct and broad notch (Fig. 3A); posterodorsal corners of propodeum armed with conspicuous thick and acute teeth (Fig. 3C); head, mesosoma, petiole, and abdominal segment III strongly foveolate (Fig. 22) [China: Yunnan]	*P. shohei*
–	Anterior clypeal margin without a distinct and broad notch (Fig. 3B); posterodorsal corner of propodeum bluntly rounded or angular (Fig. 3D), never with conspicuous teeth as above; head, dorsal mesosoma, petiole, and abdominal segment III usually granulate or punctate (Figs 8, 10, 12, 14, 15)	4
4	Frontal carinae weakly developed, short, little diverging above antennal insertions, and with narrow lateral lamellae; dorsal surface of body without erect hairs protruding from dense pubescence (Fig. 4A); smaller species (WL ≤0.80) with shorter legs (MFeI <80, MTiI <65, MBaI <40) [China: Yunnan]	*P. zhaoi*
–	Frontal carinae better developed, long, diverging above antennal insertions, and usually with broad lateral lamellae; dorsal surface of body with erect hairs protruding from dense pubescence (Fig. 4B); larger species (WL >0.95) with longer legs (MFeI >80, MTiI >65, MBaI >50)	5
5	In profile, posterodorsal corners of propodeum rounded (Fig. 5A) [China: Hunan, Zhejiang; Taiwan; Japan; South Korea; Vietnam]	*P. itoi*
–	In profile, posterodorsal corners of propodeum angular (Fig. 5B)	6
6	Scapes without erect hairs protruding from the dense pubescence; frontal carinae touching each other at their anteriormost level (Fig. 6A), their lateral lamellae relatively narrow, not conspicuously broader above antennal insertions; head (CI 85) and scapes (SI 68) relatively long [China: Yunnan]	*P. longmenense*
–	Scapes with many erect hairs protruding from the dense pubescence; frontal carinae clearly separated at their anteriormost level, not touching each other, their lamellae broad, conspicuously extending laterally above antennal insertions (Fig. 6B); head relatively broad (CI ≥89) and scapes (SI ≤63) relatively short	7
7	Propodeal declivity punctured, mostly opaque; frontal furrow conspicuous and darker than anterior cephalic dorsum (Fig. 7A); posterior face of petiolar node in profile steeper than anterior face and about half as long as anterior face (Fig. 7C) [China: Jiangxi, Zhejiang]	*P. kepingmai*
–	Propodeal declivity very shiny, at most superficially punctured; frontal furrow inconspicuous and of same color than anterior cephalic dorsum (Fig. 7B); posterior face of petiolar node in profile as steep as anterior face and less than half as long as anterior face (Fig. 7D) [China: Jiangxi, Zhejiang]	*P. bruelheidei*

Figure 1.

Petiole in profile view. A P. japonicum (CASENT0790834) B P. itoi (OKENT0016142).

Figure 2.

Petiole, abdominal segment III and anterior portion of abdominal segment IV in profile view. A P. longigaster (CASENT0790673) B P. japonicum (CASENT0790834).

Figure 3.

Anterior portion of cephalic dorsum, in full-face view (A, B), and propodeum and petiole, in profile view (C, D). A, C P. shohei (CASENT0717686) B, D P. itoi (OKENT0016142).

Figure 4.

Mesosoma dorsum in profile view. A P. zhaoi (CASENT0790671) B P. bruelheidei (CASENT0790023).

Figure 5.

Propodeum and petiole in profile. A P. itoi (OKENT0016142) B P. kepingmai (CASENT0790031).

Figure 6.

Anterior portion of cephalic dorsum in full-face view. A P. longmenense B P. bruelheidei (CASENT0790023).

Figure 7.

Anterior portion of cephalic dorsum in full-face view (A, B) and petiole in profile (C, D). A, C P. kepingmai (CASENT0790031) B, D P. bruelheidei (CASENT0790023).

Taxonomic species accounts of Chinese Proceratium

Proceratium itoi clade

Definition

Workers of this clade can be separated from all other Proceratium species by the combination of abdominal sternum IV protruding over the posterior end of abdominal sternum III, petiolar node nodiform, and body sculpture densely granulate to punctate (definition follows Baroni Urbani and de Andrade 2003).

Comments

This clade includes seven species and is restricted to east and southeast Asia. All species except P. malesianum de Andrade, 2003 and P. williamsi Mathew & Tiwari, 2000 occur in China. The species are morphologically similar, particularly in relative body proportions and indices, but can be safely separated with the identification key presented above. More detailed accounts on species delimitation and biology are reported at the species accounts below.

Proceratium bruelheidei Staab, Xu & Hita Garcia, sp. n.

http://zoobank.org/D5261D06-D21C-4149-B716-2347DC616BD5

Figs 4B, 6B, 7B, 7D, 8, 9, 24

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 SWFU.

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 CASC); 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 ZMBH); 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 ZMBH).

Cybertype. Volumetric raw data (in DICOM format), 3D rotation video (in .mp4 format, see Suppl. material 3: Video 1), still images of surface volume rendering, and 3D surface (in PLY format) of the physical holotype (CASENT0790023) in addition to montage photos illustrating head in full-face view, profile and dorsal views of the body. The data is deposited at Dryad (Staab et al. 2018, http://dx.doi.org/10.5061/dryad.h6j0g4p) and can be freely accessed as virtual representation of the type. In addition to the cybertype data at Dryad, we also provide a freely accessible 3D surface model of the holotype at Sketchfab (https://skfb.ly/6txMz).

Diagnosis

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.

Figure 8.

Proceratium bruelheidei sp. n. holotype worker (CASENT0790023). A Body in profile B Body in dorsal view C Head in full-face view.

Figure 9.

Still images from surface display volume renderings of 3D model of Proceratium bruelheidei sp. n. holotype worker (CASENT0790023). A Body in profile B Body in dorsal view C Head in dorsal view D Head in anterodorsal view E Head in anterior view F Head in ventral view G Head in profile H Mesosoma in profile I Mesosoma in dorsal view J Propodeum in posterodorsal view K Abdominal segment II and parts of III in profile L Abdominal segment II and parts of III in dorsal view M Abdominal segments II–VII in profile N Abdominal segment III and parts of II and IV in dorsal view O Abdominal segments II–VII in ventral view.

Worker measurements

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.

Worker description

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 1.5–1.6× 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.

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.

Distribution and ecology

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.

Taxonomic notes

Proceratium bruelheidei is most similar to P. kepingmai. From the other species of the P. itoi clade, P. bruelheidei can be separated by using the characters given in the ‘taxonomic notes’ of P. kepingmai below. From this species, P. 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 P. kepingmai), the shiny propodeal declivity that is only superficially punctured (densely punctured and mostly opaque in P. kepingmai), the inconspicuous frontal furrow that has the same color as the surrounding anterior cephalic dorsum (frontal furrow conspicuous and dark in P. 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 P. kepingmai), the apex of the petiolar node that is little broader than long (clearly broader than long in P. kepingmai), and the more strongly recurved abdominal segment IV (IGR 0.24–0.26) (IGR 0.30–0.32 in P. kepingmai). Additionally, P. 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 P. 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 P. kepingmai).

Variation

The variation in body size is within the normal limits of other Proceratium species and the type specimens of P. 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 P. itoi clade, as also indicated by the variation in the subpetiolar process within the type series of P. zhaoi (Xu 2000).

Proceratium itoi (Forel, 1918)

Figs 1B, 3B, 3D, 5A, 10, 11, 24

Sysphincta itoi Forel, 1918: 717 (w.), Japan

Proceratium itoi – Brown 1958: 247 (see also Baroni Urbani and de Andrade 2003: 267, Onoyama and Yoshimura 2002: 32)

Proceratium itoi – Ogata 1987: 107 (m.), Japan

Proceratium itoi – Onoyama and Yoshimura 2002: 35 (q.), Japan

Type material

Syntypes. Three pinned workers from JAPAN, Tokyo, leg. Ito (CASENT0907205, in MHNG) [images examined].

Non-type material examined

JAPAN, Fukuoka, Mt. Tachibana, 25-VII-1984, leg. S. Nomura (OKENT016137; OKENT016138; OKENT016139; OKENT016141; OKENT016142, all in OIST).

Virtual dataset

Volumetric raw data (in DICOM format), 3D rotation video (in .mp4 format, see Suppl. material 4: Video 2), still images of surface volume rendering, and 3D surface (in PLY format) of a non-type specimen (OKENT0016142) in addition to montage photos illustrating head in full-face view, profile and dorsal views of the body. The data is deposited at Dryad (Staab et al. 2018, http://dx.doi.org/10.5061/dryad.h6j0g4p) and can be freely accessed as virtual representation of the species. In addition to the data at Dryad, we also provide a freely accessible 3D surface model at Sketchfab (https://skfb.ly/6txMM).

Diagnosis

Proceratium itoi differs from the other members of the P. itoi clade by the following character combination: medium-sized species (TL 3.46–3.82); sides of head very weakly convex, almost straight, broadest at level of eyes and gently narrowing anteriorly and posteriorly, vertex weakly convex, almost straight; frontal carinae well developed, with large lamellae that extend laterally above the antennal insertions; frontal furrow inconspicuous; posterodorsal corners of propodeum rounded, propodeal declivity superficially punctured (more so dorsally) but largely shiny; posterior face of petiolar node in profile steeper as anterior face; petiole almost as broad as long (DPeI 86–93), apex of petiolar node broader than long in dorsal view; subpetiolar process developed and triangular (but may be small); in addition to dense pubescence abundant erect hairs present on scapes and dorsal surface of body, longest of those hairs shorter than maximum dorsoventral diameter of metafemur.

Figure 10.

Proceratium itoi non-type worker (OKENT0016142). A Body in profile B Body in dorsal view C Head in full-face view.

Figure 11.

Still images from surface display volume renderings of 3D model of Proceratium itoi non-type worker (OKENT0016142). A Body in profile B Body in dorsal view C Head in dorsal view D Head in anterodorsal view E Head in anterior view F Head in ventral view G Head in profile H Mesosoma in profile I Mesosoma in dorsal view J Propodeum in posterodorsal view K Abdominal segment II and parts of III in profile L Abdominal segment II and parts of III in dorsal view M Abdominal segments II–VII in profile N Abdominal segment III and parts of II and IV in dorsal view O Abdominal segments II–VII in ventral view.

Distribution and ecology

This species is widely distributed, occurring from Japan (except Hokkaido) and South Korea to Vietnam. It has been recorded from Taiwan and the Chinese provinces Zhejiang and Hunan. Thus, we expect that it will be collected from the geographically intermediate provinces in the future. No direct biological observations from China are available, but the Japanese populations are comparatively well studied (Onoyama and Yoshimura 2002). Nests are found in the soil or rotting wood of various deciduous or evergreen forest types and workers forage hypogeic or in leaf litter. Mature colonies have 100–200 workers and densities can reach 0.3 colonies per m² (Masuko 2010). Larval hemolymph feeding has been observed (Masuko 1986).

Taxonomic notes

Proceratium itoi is a typical member of its clade of intermediate size (WL 0.96–1.04) and is similar to most other species in body proportions and indices. Proceratium itoi can be separated from P. williamsi and P. zhaoi by the presence of erect hairs on the dorsal body surface (absent in P. williamsi and P. zhaoi); from P. longmenense by the presence of erect hairs on the scape (absent in P. longmenense) and by the frontal carinae separated at their anteriormost level (touching each other at their anteriormost level in P. longmenense). In P. itoi the posterodorsal corners of propodeum are rounded and this character distinguishes this species from P. bruelheidei and P. kepingmai (posterodorsal corners of the propodeum angular), which are also larger species (WL 1.03–1.10 and 1.14–1.24). The rounded posterodorsal corners of propodeum are shared between P. malesianum and P. itoi, but P. malesianum is a smaller species (WL 0.71–0.90) with a broadly rounded vertex (weakly convex, almost straight in P. itoi) and a broadly rounded petiolar node in profile (posterior face of petiolar node in profile steeper than anterior face in P. itoi).

Proceratium kepingmai Staab, Xu & Hita Garcia, sp. n.

http://zoobank.org/0233F3AD-8F60-4CBB-B64B-B0A48857CBFF

Figs 5B, 7A, 7C, 12, 13, 24

Type material

Holotype. Pinned worker from CHINA, Jiangxi Province, near the village Xingangshan, ca. 15 km SE of Wuyuan, 29°7'28"N / 117°54'40"E, 270 m asl, secondary subtropical mixed forest, Winkler leaf litter extraction, 26-III-2015, leg. Michael Staab, label “MS1836” (CASENT0790031), deposited in SWFU.

Paratype. Pinned worker from CHINA, Zhejiang Province, Gutianshan National Nature Reserve, ca. 30 km NW of Kaihua, 29°14'50"N / 118°8'10"E, 665 m asl, secondary subtropical mixed forest, Winkler leaf litter extraction, 27-IV-2015, leg. Merle Noack, label “MS1859” (CASENT0790032), deposited in ZMBH.

Cybertype. Volumetric raw data (in DICOM format), 3D rotation video (in .mp4 format, see Suppl. material 5: Video 3), still images of surface volume rendering, and 3D surface (in PLY format) of the physical holotype (CASENT0790031) in addition to montage photos illustrating head in full-face view, profile and dorsal views of the body. The data is deposited at Dryad (Staab et al. 2018, http://dx.doi.org/10.5061/dryad.h6j0g4p) and can be freely accessed as virtual representation of the type. In addition to the cybertype data at Dryad, we also provide a freely accessible 3D surface model of the holotype at Sketchfab (https://skfb.ly/6txMy).

Diagnosis

Proceratium kepingmai differs from the other members of the P. itoi clade by the following character combination: large species (TL 4.39–4.54); sides of head weakly convex, broadest at level of eyes and gently narrowing anteriorly and stronger posteriorly; vertex almost straight; very reduced eyes (OI 2–3) consisting of a single minute ommatidium; frontal carinae well developed, with large lamellae that extend laterally above the antennal insertions; frontal furrow darker than the surrounding anterior cephalic dorsum; posterodorsal corners of the propodeum broadly angular; propodeal declivity densely punctured, mostly opaque; posterior face of petiolar node in profile steeper than anterior face and about half as long as anterior face; apex of petiolar node distinctly broader than long in dorsal view; in addition to dense pubescence, erect hairs present on scapes and dorsal surface of body, longest of those hairs at most as long as the maximum dorsoventral diameter of metafemur.

Figure 12.

Proceratium kepingmai sp. n. holotype worker (CASENT0790031). A Body in profile B Body in dorsal view C Head in full-face view.

Figure 13.

Still images from surface display volume renderings of 3D model of Proceratium kepingmai sp. n. holotype worker (CASENT0790031). A Body in profile B Body in dorsal view C Head in dorsal view D Head in anterodorsal view E Head in anterior view F Head in ventral view G Head in profile H Mesosoma in profile I Mesosoma in dorsal view J Propodeum in posterodorsal view K Abdominal segment II and parts of III in profile L Abdominal segment II and parts of III in dorsal view M Abdominal segments II–VII in profile N Abdominal segment III and parts of II and IV in dorsal view O Abdominal segments II–VII in ventral view.

Worker measurements

Holotype.TL 4.39; EL 0.02; SL 0.57; HL 0.92; HLM 1.08; HW 0.86; WL 1.14; MFeL 0.71; MTiL 0.60; MBaL 0.44; PeL 0.45; PeW 0.36; LT3 0.64; LS4 0.32; LT4 1.08; OI 2; CI 92; SI 60; MFeI 83; MTiI 70; MBaI 51; DPeI 80; IGR 0.30; ASI 169.

Paratype.TL 4.54; EL 0.03; SL 0.59; HL 0.98; HLM 1.14; HW 0.90; WL 1.24; MFeL 0.79; MTiL 0.65; MBaL 0.48; PeL 0.46; PeW 0.37; LT3 0.65; LS4 0.34; LT4 1.05; OI 3; CI 93; SI 62; MFeI 88; MTiI 72; MBaI 53; DPeI 80; IGR 0.33; ASI 161.

Worker description

In full-face view, head slightly longer than broad (CI 92–93), sides weakly convex, broadest at the eye level and gently narrowing anteriorly and (stronger) posteriorly, vertex weakly convex, almost straight. 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 well 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. Eyes reduced, minute (OI 2–3), consisting of a single ommatidium and located on midline of head. Antennae 12-segmented, scapes short (SI 60–62), not reaching posterior head margin and thickening apically. Mandibles elongate and triangular, 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 slightly longer than maximum head length including mandibles (WL 1.14–1.24 vs. HLM 1.08–1.14). 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 propodeal spiracle rounded, at mid height, opening of spiracle slightly facing posteriorly. Legs moderately long; 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 half as long and steeper than anterior face; petiole in dorsal view longer than broad but apex of node clearly broader than long; ventral process moderately developed on anterior petiole, with a relatively indistinct rectangular projection.

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, recurved (IGR 0.30–0.33) and posteriorly strongly rounded, with a lamella on its anterior border around the constriction to abdominal segment III, this lamella thicker ventrally than dorsally; abdominal tergum IV 1.6–1.7× longer than abdominal tergum III (ASI 161–169); 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, the dorsal surfaces of body interspersed with 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 single hairs), and legs (ventral faces of femora and tibiae with many hairs, dorsal faces with single hairs); the longest hairs on dorsal surface of body at most as long as the maximum dorsoventral diameter of metafemur. Mandibles striate; entire body including propodeal declivity 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, abdominal segments V–VII very superficially punctured and shiny. Body color uniformly orange brown to reddish brown, vertex of head slightly darker, frontal furrow conspicuously darker than surrounding cephalic dorsum, legs, antennal funiculus, and abdominal segments V–VII yellowish brown.

Etymology

The species epithet is a patronym in honor of the Chinese botanist Prof. Keping Ma and his efforts in establishing the BEF-China project and promoting biodiversity research and nature conservation in China. All specimens of this species were collected in old-growth subtropical forest, an ecosystem Prof. Ma has investigated in detail.

Distribution and ecology

Both specimens were collected in secondary mixed evergreen broadleaved forest of relatively advanced age, as indicated by the presence of large trees. The paratype was collected within the Gutianshan National Nature Reserve (Yu et al. 2001, Bruelheide et al. 2011, Staab 2014), one of the larger remaining fragments of subtropical broadleaved forest in southeast China. The forest at this locality (the type locality is a similar but much smaller forest fragment) is on sloped land and rich in plant species; more than 250 woody species have been recorded on about 8000 ha. Approximately 50% of the woody species are deciduous but the tree layer is dominated by evergreen species including Castanopsis eyrei (Fagaceae) (Champ. ex Benth.) Tutch., Cyclobalanopsis glauca (Fagaceae) (Thunb.) Oerst., Machilus thunbergii (Lauraceae) Sieb. et Zucc., and Schima superba (Theaceae) Gardn. et Champ. No direct observations of biology and natural history are available for P. kepingmai.

Taxonomic notes

Proceratium kepingmai is the largest (WL 1.14–1.24) member of the P. itoi clade and has, even for eye-bearing Proceratium, very minute eyes (OI 2–3). From each of the species in the clade with very similar body proportions (particularly indices) that also have erect hairs on the dorsal surface of the body (P. itoi, P. longmenense, P. malesianum, P. bruelheidei; no erect hairs, only dense pubescence in P. williamsi, P. zhaoi) it can safely be separated by one or more characters. In P. kepingmai the posterodorsal corner of the propodeum is angular (rounded in P. itoi and P. malesianum), which is also the case for P. longmenense and P. bruelheidei. However, P. longmenense lacks erect hairs on the scape (at least some erect hairs present in P. kepingmai and P. bruelheidei), has a relatively narrower head (CI 85) with longer scapes (SI 68) (CI 92–93 and SI 60–62 in P. kepingmai), and frontal carinae that touch each other at their anteriormost level (clearly separated in P. kepingmai and P. bruelheidei). With P. bruelheidei, the most similar species, P. kepingmai also shares the broad frontal carinae that have large lamellae and are conspicuously extended laterally above the antennal insertions (not extended and narrower in P. longmenense). In contrast, P. kepingmai differs from P. bruelheidei by the shape of the head in full-face view that has convex sides, which are broadest at the level of the eyes and narrow weakly anteriorly and more strongly posteriorly towards to almost straight vertex (sides straight, not narrowing anteriorly and vertex convex in P. bruelheidei), the densely punctured and mostly opaque propodeal declivity (sparsely and superficially punctured and very shiny in P. bruelheidei), the conspicuous frontal furrow that is darker than the rest of the surrounding anterior cephalic dorsum (inconspicuous and of same color in P. bruelheidei), the posterior face of petiolar node in profile steeper than the anterior face of the node and about half as long as the anterior face (posterior face as steep as anterior face and less than half as long in P. bruelheidei), the apex of the petiolar node that is clearly broader than long in dorsal view (less broad than long in P. bruelheidei), and relatively fewer and shorter erect hairs (see P. bruelheidei for details).

Variation

Apart from the small difference in body size (WL 1.14 vs. 1.24) there is no observable variation between the two specimens.

Proceratium longmenense Xu, 2006

Figs 6A, 14, 25

Proceratium longmenense Xu, 2006: 154 (w.), China

Type material

Holotype. Pinned worker from CHINA, Yunnan Province, Kunming City, Xishan Mountain Forest Park, Longmen, subtropical evergreen broadleaf forest, 2050 m asl, 5-V-2001, leg. Zhenghui Xu, No. A00514 (in SWFU) [examined].

Diagnosis

Proceratium longmenense differs from the other members of the P. itoi clade by the following character combination: medium-sized species (TL 3.2); sides of head and vertex weakly convex, almost straight; head (CI 85) and scapes (SI 68) relatively long; frontal carinae developed, their lateral lamellae relatively narrow, touching each other at their anteriormost level, not conspicuously broader above antennal insertions; posterodorsal corners of the propodeum broadly angular; posterior face of petiolar node in profile shorter and steeper than anterior face; petiole almost as broad as long (DPeI 91); subpetiolar process developed, roughly trapezoid; in addition to dense pubescence erect hairs present on dorsal surface of body, but only sparsely on head, scapes without erect hairs.

Figure 14.

Proceratium longmenense holotype worker. A Body in profile B Body in dorsal view C Head in full-face view.

Distribution and ecology

This species is only known from the holotype that was collected in subtropical evergreen broadleaved forest at 2050 m asl. No direct observations of biology and natural history are available for P. longmenense.

Taxonomic notes

The unique hair patterns separate P. longmenense from the other species of the P. itoi clade. Proceratium williamsi and P. zhaoi have no erect hairs that protrude from the dense pubescence on the dorsal surface of body (hairs present in P. longmenense, but relatively sparsely, especially on head). All other species (P. bruelheidei, P. itoi, P. kepingmai, P. malesianum) have also such hairs on the scapes (absent on scapes in P. longmenense). In addition to hairs, which may be worn down in old specimens, P. longmenense is unique by the relatively long scapes (SI 68) combined with the relatively narrow head (CI 85). Among the other Chinese P. itoi clade species, it differs furthermore from P. zhaoi in size (WL 0.97; WL<80 in P. zhaoi), from P. itoi by the shape of the posterodorsal corners of the propodeum (broadly angular; rounded in P. itoi), and from P. bruelheidei, P. itoi, and P. kepingmai by the lamellae of the frontal carinae (touching each other at their anteriormost level; separated in the other three species).

Proceratium zhaoi Xu, 2000

Figs 4A, 15, 16, 17, 25

Proceratium zhaoi Xu, 2000: 435 (w.q.), China

Proceratium nujiangense Xu, 2006: 153 (w.q.), China, syn. n.

Type material

Of P. zhaoi: Holotype. Pinned worker from CHINA, Yunnan Province, Menghai County, Meng’a Town, Papo Village, 1280 m asl, deciduous broadleaved forest, soil sample, 10-IX-1997, leg. Zheng-Hui Xu, No. A97-2338 (in SWFU) [examined].

Paratypes. Six pinned workers and 24 alate females; one worker with same data as holotype; all other paratypes with same data as holotype but No. A97-2380 (CASENT0235334 in CASC; CASENT0790671 and all other paratypes in SWFU) [all examined].

Of P. nujiangense: Holotype. Pinned worker from CHINA, Yunnan Province, Baoshan City, Lujiang Town, Bawan, 1500 m asl, Pinus yunnanensis forest on east slope of Nujiang River Valley, 11-VIII-1998, leg. Qizhen Long, label “A98-1964” (in SWFU) [examined].

Paratypes. Seven pinned workers and 10 queens with same data as holotype but No. A98-1995, No. A98-1997, No. A98-2010, No. A98-2016, No. A98-2029 (CASENT0790672 and all other paratypes in SWFU) [all examined].

Virtual dataset

Volumetric raw data (in DICOM format), 3D rotation videos (in .mp4 format, see Suppl. material 6: Video 4 for P. zhaoi and Suppl. material 7: Video 5 for P. nujiangense), still images of surface volume rendering, and 3D surfaces (in PLY format) of a paratype of P. zhaoi (CASENT07900671) and a paratype of P. nujiangense (CASENT0790672) in addition to montage photos illustrating head in full-face view, profile and dorsal views of the body. The data is deposited at Dryad (Staab et al. 2018, http://dx.doi.org/10.5061/dryad.h6j0g4p) and can be freely accessed as virtual representations of the species. In addition to the data at Dryad, we also provide freely accessible 3D surface models at Sketchfab (https://skfb.ly/6txOT and https://skfb.ly/6txOL).

Diagnosis

Proceratium zhaoi differs from the other members of the P. itoi clade by the following character combination: small species (TL 2.0–2.8, WL 0.66–0.80; measurements and indices use data from the original descriptions); of head weakly convex, broadest at level of eyes and gently narrowing anteriorly and posteriorly, posterior head margin weakly concave to almost straight; frontal carinae developed, their lateral lamellae relatively narrow, not extending over antennal insertions; posterodorsal corners of propodeum bluntly angled; posterior face of petiolar node, in profile, shorter and steeper than anterior face, dorsum of node broadly rounded, petiole as long as broad or broader than long (DPeI 98–110), subpetiolar process developed, relatively variable, varying in size and shape (from rectangular to triangular to acutely toothed); only dense pubescence, no erect hairs on dorsum of body, head, and scapes.

Figure 15.

Proceratium zhaoi paratype worker (CASENT0790671). A Body in profile B Body in dorsal view C Head in full-face view.

Figure 16.

Still images from surface display volume renderings of 3D model of Proceratium zhaoi paratype worker (CASENT0790671). A Body in profile B Body in dorsal view C Head in dorsal view D Head in anterodorsal view E Head in anterior view F Head in ventral view G Head in profile H Mesosoma in profile I Mesosoma in dorsal view J Propodeum in posterodorsal view K Abdominal segment II and parts of III in profile L Abdominal segment II and parts of III in dorsal view M Abdominal segments II–VII in profile N Abdominal segment III and parts of II and IV in dorsal view O Abdominal segments II–VII in ventral view.

Figure 17.

Still images from surface display volume renderings of 3D model of Proceratium zhaoi paratype worker of P. nujiangense (CASENT0790672). A Body in profile B Body in dorsal view C Head in dorsal view D Head in anterodorsal view E Head in anterior view F Head in ventral view G Head in profile H Mesosoma in profile I Mesosoma in dorsal view J Propodeum in posterodorsal view K Abdominal segment II and parts of III in profile L Abdominal segment II and parts of III in dorsal view M Abdominal segments II–VII in profile N Abdominal segment III and parts of II and IV in dorsal view O Abdominal segments II–VII in ventral view.

Distribution and ecology

This species is only known from two locations at mid elevation in forests of southern and western Yunnan Province. The original description reported 45 workers in the type colony (Xu 2000) and no other data on natural history have been published. However, the relatively short legs suggest a purely hypogeic life style, which conforms to the fact that specimens were extracted from soil samples.

Taxonomic notes

Even though at the beginning of this study we treated P. nujiangense and P. zhaoi as distinct species, thorough examinations combining traditional microscopy with micro-CT scans proved that there are no morphological characters separating them. The virtual comparisons of type specimens of both taxa showed that there are no morphological differences, a fact that is not easy to observe by comparing physical specimens. The types are hairy, dirty, and mounted in ways that hide most important characters, as it is typical for most Proceratium specimens. Furthermore, the main character used by Xu (2006) to separate the species was the subpetiolar process, which has been used for species diagnostics in previous studies (Baroni Urbani and de Andrade 2003, Hita Garcia et al. 2014, 2015). However, these works either had very little material for the assessment of intraspecific variation and/or treated different clades of Proceratium. Our study shows that the subpetiolar process is extremely variable within the P. itoi clade and refrain from using it for species delimitations. As a matter of fact, the variation of the subpetiolar process was already noted in the description of P. zhaoi (Xu 2000). Reexamination of all type specimens of both species also revealed a comparatively high degree of variation and overlap in the form of the posterodorsal corner of the propodeum and the width of the propodeal node. In addition, the morphometric ranges of P. nujiangense and P. zhaoi overlap and form a continuum, and there are no significant differences in proportions since all indices are identical. Considering these similarities in light of the newly available images and micro-CT data, we propose treating P. nujiangense as a junior synonym of P. zhaoi.

This species was not mentioned in the revision of Baroni Urbani and de Andrade (2003), potentially because the authors were not aware of its description shortly before the completion of their monograph. Despite some size variation (TL 2.0–2.8), the relative body proportions of P. zhaoi are constant (CI 84–90, SI 61–66). Proceratium zhaoi is the smallest (WL 0.66–0.80) member of the P. itoi clade. It can be distinguished from all other P. itoi clade species (except for P. williamsi) by the absence of erect hairs that protrude through the dense pubescence on the dorsal body surface. Proceratium williamsi also lacks hairs on the dorsal body surface, but is larger (WL 0.80–0.92), has stronger developed frontal carinae and relatively more slender and longer legs. The relatively weakly developed frontal carinae and the short legs (MFeI <80, MTiI <65, MBaI <40) make P. zhaoi also unique among the Chinese P. itoi clade species.