Proceratium japonicum

Proceratium japonicum lives on the ground in evergreen forests (Japanese Ant Image Database).

Identification
Staab et al. (2018) - Proceratium japonicum differs from the other east Asian members of the Proceratium silaceum clade by the following character combination: medium-sized species (WL 0.72–1.00); sides of head convex, broadest above the level of eyes; anterior clypeal margin not protruding and slightly notched; frontal carinae well developed and widely separated, with large lamellae that extend laterally above the antennal insertions and reach posteriorly almost to the level of eyes; frontal furrow strongly developed; petiole squamiform, in profile not or only weakly narrowing dorsally, the base as or almost as broad as the apex, in dorsal view relatively narrow (DPeI <150); subpetiolar process developed, subtriangular, directing backwards; sculpture not deeply impressed, on abdominal segment III granulate and relatively regular; in addition to dense pubescence, some suberect to erect hairs present on scapes and dorsal surface of body.

According to Baroni Urbani and de Andrade (2003) Proceratium japonicum is most similar to Proceratium numidicum which is, however, a geographically widely separated species occurring in the eastern Mediterranean and northern Africa. We were not able to examine Proceratium japonicum material from China. In Japan, specimens from the Ryukyu and Yaeyama islands are smaller than from the main islands (Onoyama and Yoshimura 2002, Baroni Urbani and de Andrade 2003), explaining the relatively large variation in body size. From Proceratium longigaster, the only other Proceratium silaceum clade species in China and east Asia, Proceratium japonicum can be separated by the shape of the petiole in profile that not or only weakly narrows dorsally (clearly narrowing dorsally, broader on the base than on the apex in Proceratium longigaster). Also, the petiole in dorsal view is narrower in Proceratium japonicum (DPeI <150) than in Proceratium longigaster (DPeI ≥155). Furthermore, the frontal carinae in Proceratium japonicum reach posteriorly almost to the level of eyes (shorter and ending well below the level of eyes in Proceratium longigaster). Proceratium japonicum has only relatively few suberect to erect hairs that protrude from the dense pubescence on the dorsal body; those hairs are straight (never shaggy) and do not conspicuously project from LT3 over the constriction between LT3 and LT4 (many shaggy hairs projecting in Proceratium longigaster); if single longer hairs are present, then they are not shaggy.

Volumetric raw data (in DICOM format), a 3D rotation video (in .mp4 format, see Suppl. material 8: Video 6), 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 a non-type specimen (CASENT0790834) were all generated as part of this study (Staab et al 2018). 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 can be viewed online at Sketchfab.

Distribution based on Regional Taxon Lists
Oriental Region: Taiwan. Palaearctic Region: China, Japan.

Biology
Staab et al. (2018) - This species is common from Japan (except Hokkaido) to Taiwan and usually collected in forests of relatively low elevation. It has also been reported from Yunnan Province in China. Thus, it is not unlikely that more records from the southern and eastern Chinese mainland will appear in the future if sampling effort is increased. No direct biological observations from China are available. In Japan, nests are typically found in deadwood in evergreen broadleaved forest (Onoyama and Yoshimura 2002). Colony size can reach over 150 workers and larval haemolymph feeding has been observed (Masuko 1986).

Nomenclature

 *  japonicum. Proceratium japonicum Santschi, 1937h: 362, fig. 1 (w.) JAPAN. Onoyama & Yoshimura, 2002: 35 (q.m.). Senior synonym of formosicola: Onoyama, 1991: 695. See also: Baroni Urbani & De Andrade, 2003b: 368.
 * formosicola. Proceratium formosicola Terayama, 1985c: 406, figs. 1-4 (w.q.) TAIWAN. Junior synonym of japonicum: Onoyama, 1991: 695.

Worker
Baroni Urbani and de Andrade (2003) - Head slightly longer than broad and with weakly convex sides. Vertex in full face view gently convex. Clypeus reduced, slightly surpassing the antennal sockets. Anterior border of the clypeus truncate. Frontal carinae far from each other, slightly covering the antennal insertions. Lateral expansions of the frontal carinae little raised, diverging on the two anterior fourths, converging on the third fourth, subparallel and carinate only on the last fourth. Frontal area gently concave on the three anterior fourths and with a central longitudinal carina starting from the last fourth and prolonging posteriorly. Head anterolaterally with a thick, short, longitudinal carina. Genal carinae distinct, each carina corresponding to the external border of a deep sulcus. Eyes visible as a dark dot below the integument, small and on the middle o l the head sides. First funicular joint slightly longer than broad. Funicular joints 2-10 broader than long. Last funicular joint as long as the sum of joints 7-10. Scapes short of the vertexal margin and gently thickening apically. Masticatory margin of the mandibles with 9-11 denticles before the pointed apical tooth. Palp formula 2,2.

Mesosoma in profile convex anteriorly, declivous posteriorly and shorter than the maximum head length (mandibles included). Pronotal and propodeal sutures absent. Basal face of the propodeum declivous posteriorly. Declivous face of the propodeum flat. Area between basal and declivous faces of the propodeum gently concave, less carinate dorsally than in numidicum and laterally angulate or denticulate. Sides of the declivous face of the propodeum carinate. Propodeal spiracle round and above mid height in lateral view.

Petiole subrectangular, broader than in numidicum. Anterior border of the petiole straight and anterolaterally carinate. Posterior broader of the petiolar node gently convex or subangulate. Ventral process of the petiole lamelliform and directed backwards. Postpetiolar sternite anteromedially with a marked subtriangular projection, gently convex posteriorly in side view. Constriction between postpetiole and gaster impressed. Gastral tergite I about 1/3 longer than the postpetiole and convex on the curvature. Remaining gastral tergites and sternites curved ventrally.

Legs not very short. All tibiae with a pectinate spur. Spurs of fore legs without basal spine. Fore basitarsi longer than the mid ones. Hind basitarsi about 1/4 shorter than hind tibiae. Second tarsomere of hind legs shorter than pretarsus. Pretarsal claws simple. Arolia absent.

Sculpture. Head reticulate-punctate and rugulose, the reticulation and the rugosities broader on the sides. Mesosoma, petiole and postpetiole punctate, the punctures smaller on the anterior half of the mesosoma. Posterior half of the mesosoma and sides of the postpetiole with additional, irregular reticulation. Gaster smooth and with minutely piligerous punctures, the punctures denser and mixed with superficial reticulation on the sides. Legs punctate.

Body covered by hairs of three main types: (1) short, dense, suberect or subdecumbent on the whole body, sparse on the funicular joints; (2) longer than type (1), erect on the whole body, absent on the funiculi; (3) shorter than hair type (1), dense and decumbent on the funicular joints only. In addition the funicular joints bear whitish, thick, appressed, sparse hairs, and the scapes with sparse hairs similar to type (2) but slightly shorter.

Colour. Yellow to brown with slightly lighter antennae and legs. Some specimens have the posterior half of the head dorsum darker.

Measurements in mm and Indices: TL 2.84-3.32; HL 0.63-0.75; HW 0.59-0.71; EL 0.03-0.07; SL 0.42-0.49; WL 0.78-0.91; PeL 0.19-0.24; PeW 0.30-0.35; HFeL 0.47-0.56; HTiL 0.38-0.46; HBaL 0.29-0.34; LS4 0.33-0.41; LT4 0.65-0.75; CI 93.6-94.7; SI 64.6-66.6; IGR 0.51-0.55.

Queen
Baroni Urbani and de Andrade (2003) - Differing from the worker in the following details: eyes large, ¼ of the head length, composed by many facets and with ocular pilosity. Ocelli well developed.

Mesosoma robust and convex in side view. Parapsidal furrows masked. Scutellum with the sides gently converging posteriorly and with the posterior border round. Dorsum of the scutellum with a longitudinal carina prolonging to the posterior half of the mesonotum. Metanotum with a pointed tooth. Basal face of the propodeum medially concave. Area between basal and declivous faces of the propodeum carinate and with a small tooth on each side.

Fore wings of our type 4, hind wings of our type 2 and 3 as defined in the description of the genus.

Measurements in mm and Indices: TL 3.48-3.75; HL 0.69-0.73; HW 0.67-0.72; EL 0.19-0.24; SL 0.47-0.49; WL 0.98-1.10; PeL 0.24-0.26; PeW 0.38-0.40; HFeL 0.58-0.60; HTiL 0.47-0.48; HBaL 0.38-0.39; LS4 0.46; LT4 0.84-0.86; CI 97.1-98.6; SI 67.1-68.1; IGR 0.53-0.55.

Male
Baroni Urbani and de Andrade (2003) - Head as broad as long or slightly broader than long. Vertex in full face view convex. Vertexal margin carinate. Clypeus dorsally variably convex and with subround or straight anterior border. Frontal carinae thin, low and parallel. Frontal area concave; postero-lateral borders of the concavity variably marginate, the margins converging posteriorly and connected to a longitudinal carina. Ocelli large. Compound eyes large and situated mostly on the anterior part of the head sides. Scapes not reaching the anterior ocellus. First funicular joint about as broad as long and 1/3 shorter than the second joint. Joints 2-12 longer than broad. Last funicular joint slightly longer than the sum of joints 10-11. Mandibles edentate and only with a pointed apical tooth. Palp formula 5,2.

Mesosoma robust. Pronotum and anterior third of mesonotum almost perpendicular to the posterior two thirds of the mesonotum. Posterior two thirds of mesonotum almost flat. Parapsidal furrows marked. Scutellum as high as the mesonotum; sides of the scutellum converging into a round posterior border. Basal and declivous propodeal faces slightly convex in side view. Basal face of the propodeum slightly declivous posteriorly. Declivous face of the propodeum flat. Area between basal and declivous faces of the propodeum gently concave and laterally subangulate. Declivous face of propodeum laterally superficially carinate. Metalloturn with a median lamellaceous tooth. Propodeal lobes round and lamellaceous. Propodeal spiracles small.

Petiole in side view sloping anteriorly in the two anterior fourths, subconvex in the third fourth and sloping in the posterior fourth. Sides of the petiole in dorsal view weakly convex. Anterior border of the petiole straight and laterally carinate. Subpetiolar process very small and subtriangular. Postpetiole anteriorly broader than the petiole; postpetiolar sides diverging posteriorly. Anterior border of the postpetiolar sternite with a superficial triangular "lip". Gastral tergite I in side view convex. Gastral sternite I large. Remaining gastral tergites and sternites slightly curved ventrally.

Legs as in the worker but more elongate. Hind basitarsi slightly shorter than hind tibiae.

Fore wings of our type 4, hind wings of our type 2 and 3 as defined in the description of the genus.

Sculpture. Head and mesosoma punctate, reticulorugose, the reticulation large on the mesonotum and larger than on mesonotum on the basal face of the propodeum and metapleurae. Petiole, postpetiole, gaster and legs smooth and with minute piligerous punctures slightly denser on the postpetiole. Body covered by hairs of three main types: (1) short, dense, suberect or subdecumbent, suberect, sparse and slightly shorter on the funicular joints; (2) longer than type (1), erect or subdecumbent, slightly longer on the gaster, absent on the antennae; (3) shorter than hair type (1), dense and decumbent on the funicular joints. In addition the funicular joints bear whitish, thick, appressed, sparse hairs, and the scapes with sparse hairs similar to type (2) but slightly shorter.

Colour. Dark brown-black with lighter mandibles, antennae and legs.

Measurements in mm and Indices: TL 2.52-3.19; HL 0.48-0.58; HW 0.50-0.58; EL 0.26-0.28; SL 0.23-0.28; WL 0.84-1.08; PeL 0.19-0.21; PeW 0.21-0.25; HFeL 0.48-0.62; HTiL 0.38-0.48; HBaL 0.32-0.46; LS4 0.32-0.44; LT4 0.58-0.72; CI 100.0- 104.2; SI 47.9-49.1; IGR 0.55-0.59.

Type Material
Baroni Urbani and de Andrade (2003) - Type locality: Honshu, Japan. Type material: 3 syntype workers labelled: "Japon, Oshima, Iya, Honshiu, 10.VI.28, Kisato, Proceratium japonicum Sant., Dr. Santschi F. 1937", in, examined.

Proceratium formosicola Type locality: Taiwan. Type material: 1 paratype worker labelled: 15.VIII.1980, Lushan (ca. 1000 m Alt.), Nantou Hsien, Taiwan, M. Terayama leg., Paratype, Proceratium formosicola, Terayama, 1985, in, examined.

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