Eburopone easoana, Yamada & Nguyen & Eguchi, 2023

Yamada, Aiki, Nguyen, Dai Dac & Eguchi, Katsuyuki, 2023, First discovery of the ant genus Eburopone Borowiec, 2016 (Hymenoptera, Formicidae, Dorylinae) in the Oriental realm, with description of a new species from Vietnam, ZooKeys 1184, pp. 1-17 : 1

publication ID	https://dx.doi.org/10.3897/zookeys.1184.109702
publication LSID	lsid:zoobank.org:pub:3D745E43-FB6C-48A8-B089-DDAEE1A422BB
DOI	https://doi.org/10.5281/zenodo.10170542
persistent identifier	https://treatment.plazi.org/id/73CBF0E9-4D91-4EAD-952B-F324E03D370E
taxon LSID	lsid:zoobank.org:act:73CBF0E9-4D91-4EAD-952B-F324E03D370E
treatment provided by	ZooKeys by Pensoft
scientific name	Eburopone easoana
status	sp. nov.

Treatment

Eburopone easoana sp. nov.

Figs 2 View Figure 2 , 3 View Figure 3 , 4 View Figure 4 , 5 View Figure 5 , 6 View Figure 6 , 7 View Figure 7

Type material.

Holotype. Vietnam • worker; Vietnam, Dak Lak Province, Ea Kar District, Ea So Nature Reserve; 12.9676°N, 108.5230°E, 478 m alt.; 17 Sept. 2019; K. Eguchi leg.; colony code Eg17ix19-297; IEBR.

Paratypes. 6 workers and 2 dealate queens from the same colony as the holotype; IEBR, MCZC, MHNG, MNHAH.

Non-type material examined.

Two workers from the same colony as the type series, used for SEM and dissecting observations (one of these was used also for DNA barcoding).

DNA barcode.

A partial mitochondrial COI sequence of 658 bp length determined from a non-type worker (the same colony as the type series) is deposited at GenBank: accession number, LC776907.

Worker diagnosis.

Body rather bicolored: abdominal segments III-VII distinctively paler-colored than most surfaces of cranium and mesosoma. Frontal line distinct, extending a little beyond mid-length of cranium. Occipital corner in lateral view strongly produced posteriad to form conspicuous angle. Anterior (frontoclypeal) margins of torulo-posttorular complex not forming conspicuous lobes protruding over anterior clypeal margin in full-face view. Mandibles when closed in full-face view forming only a little space between anterior clypeal margin and mandibles. Promesonotal suture faint and inconspicuous. Petiole in dorsal view almost as long as or slightly longer than wide, with weakly convex lateral margins. Subpetiolar process in lateral view rounded lobate, with anterobasal margin weakly emarginate; posteroventral slope gentle, weakly concave. Abdominal segment III in dorsal view subtrapezoidal, strongly wider posteriorly, distinctly wider than long.

Worker measurements (in mm) and indices.

Holotype: HL 0.63, HW 0.55, SL 0.31, WL 0.86, DML 0.73, PH 0.31, PW 0.37, MFL 0.43, PTH 0.26, PTL 0.29, PTW 0.28, A3L 0.35, A3W 0.46, A4L 0.58, A4W 0.62, CI 87, SI 50, DMI 43, DMI2 85, LMI 36, MFI 79, LPI 111, DPI 97, DA3I 131, DA4I 107.

Paratypes (N = 6): HL 0.63-0.65, HW 0.55-0.57, SL 0.31-0.33, WL 0.89-0.92, DML 0.74-0.80, PH 0.32-0.35, PW 0.37-0.40, MFL 0.44-0.47, PTH 0.27-0.29, PTL 0.30-0.33, PTW 0.29-0.32, A3L 0.37-0.43, A3W 0.47-0.51, A4L 0.56-0.64, A4W 0.64-0.66, CI 86-88, SI 48-51, DMI 42-43, DMI2 84-87, LMI 36-38, MFI 80-83, LPI 111-114, DPI 95-98, DA3I 118-130, DA4I 103-112.

Queen measurements (in mm) and indices.

Paratypes (N = 2): HL 0.70-0.72, HW 0.58-0.61, EL 0.19-0.20, OL 0.05-0.06, SL 0.35-0.36, WL 1.18-1.20, DML 1.07-1.08, PW 0.57-0.58, MFL 0.51-0.53, PTH 0.31, PTL 0.35-0.36, PTW 0.35-0.37, A3L 0.48-0.49, A3W 0.56-0.58, A4L 0.82, A4W 0.73-0.75, CI 84, SI 49-50, EI 28, OI 7-8, DMI 48, DMI2 90-91, MFI 87-88, LPI 111-117, DPI 100-101, DA3I 115-119, DA4I 89-91.

Description.

Worker. Body coloration. Body rather bicolored: cranium, mesosoma, and petiole, mostly dark reddish brown; antennae, anterior part of cranium, mandibles, legs, and abdominal segments III-VII paler brownish to yellowish (Fig. 2A-C View Figure 2 ). Pleural endophragmal pit conspicuously blackish.

Head structure. Cranium in full-face view subrectangular, 1.14-1.17 × longer than wide (CI, 86-88), with convex lateral margins; posterior margin widely weakly concave. Occipital corner in lateral view strongly produced posteriad to form conspicuous angle. Occipital carina (oc, Fig. 3A, B View Figure 3 ) distinct and completely encircles occiput, forming inconspicuous and slightly undulate carina dorsally and a conspicuous flange lateroventrally. Frontal line (fl, Figs 2A View Figure 2 , 3C, D View Figure 3 ) distinct, extending a little beyond mid-length of cranium. Torulo-posttorular complex (tptc, Fig. 3C-E View Figure 3 ) in full-face view arrow-like shaped with narrowed median part; anterior (frontoclypeal) margins not forming conspicuous lobes protruding over anterior clypeal margin in full-face view; maximal width of posterior arrowhead-like part a little shorter than major diameter of antennal socket. Anterior clypeal margin evenly weakly concave in full-face view. Lateroclypeal teeth (lct, Fig. 3A, C, D View Figure 3 ) large, rounded lobate, strongly protruding latero-anteriad to form anteriormost points of cranium, lateroventrally with a weak protrusion (black arrows in Fig. 3A, C View Figure 3 ). Parafrontal ridges (pfr, Fig. 3A, C-E View Figure 3 ) conspicuous and strongly elevated, turning at posteriorly to incompletely surround antennal sockets, and forming well-marginated subtriangular mound-like lobes; its lateral margins evenly rounded arc-like in full-face view; minimal distance from medialmost end of parafrontal ridge to margin of torulo-posttorular complex in full-face view as long as major diameter of antennal socket. Eye and ocelli completely absent. Antenna 12-merous; scape short, just reaching approximately mid-length of cranium when laid backward; antennomere XII distinctively longer than summed length of three preceding antennomeres IX-XI. Mandible subtriangular, with rounded obtuse basal angle and blunt apex, when closed in full-face view forming only a little space between anterior clypeal margin and mandibles (basal angles nearly reaching center line of cranium when mandibles closed); masticatory margin virtually edentate but with a series of feeble inconspicuous denticles. Postgenal ridge (pgr, Fig. 4A View Figure 4 ) externally recognizable as a broad cross-ribbed furrow, ending a little before the level of occipital carina. Hypostomal teeth (hyt, Fig. 4A View Figure 4 ) large and conspicuous with rounded apex in ventral view. Atalar acetabulum (ala, Figs 3C View Figure 3 , 4A View Figure 4 ) strongly produced anterolaterad. Labrum subrectangular with distal margin weakly bilobed with a small median notch; lateral labral process (lbrp, Fig. 4B View Figure 4 ) not visible in frontal view, strongly produced distad and truncated tooth-like. Maxillary palps bi-merous; palpomere II elongate, much longer than palpomere I (Fig. 4C View Figure 4 ). Labial palps tri-merous; palpomere III distinctly shorter than preceding palpomeres; palpomere II strongly curved basally (Fig. 4D View Figure 4 ).

Mesosomal structure. Mesosoma with evenly and slightly convex dorsum in lateral view (Fig. 5A View Figure 5 ); lateral margins in dorsal view almost parallel, weakly and widely compressed laterally around mesopleura (Fig. 5B View Figure 5 ). Pronotal flange only weakly marginated posteriorly from collar. Pronotum and mesopleuron unfused in terms of absence of sclerotized fusion, with dorsal part of pronotomesopleural junction apparently connected by a narrow intersegmental membrane (Fig. 5A, C View Figure 5 ). Promesonotal suture inconspicuous, only faintly recognizable as a shallow groove (pmns, Fig. 5D View Figure 5 ; may be hardly recognizable under normal optical observation as in Fig. 5B View Figure 5 , but the weak suture can be recognizable by changing angle of observation or lighting condition). Concavity surrounding pleural endophragmal pit (epp, Fig. 5A, C View Figure 5 ) deep and conspicuous. Propodeal declivity only weakly marginate dorsally, almost immarginate laterally; dorsal margin weakly arched anteriad in dorsal view (Fig. 5A, B View Figure 5 ). Posterodorsal corner of propodeum in lateral view blunt, only weakly angulated. Propodeal lobe evenly rounded in lateral view. Pretarsal claws simple without teeth.

Metasomal structure. Petiole (abdominal segment II) in dorsal view 1.02-1.05 × longer than wide (length measured from anterodorsal corner to posterior margin of posterior petiolar peduncle; DPI, 95-98), with weakly convex lateral margins; posterior margin of posterior petiolar peduncle slightly arched anteriad (Fig. 5B View Figure 5 ). Dorsal outline of petiole in lateral view roundly convex; anterolateral petiolar carina dorsally protrude to form a stout prominence with acute apex. Subpetiolar process in lateral view rounded lobate, with anterobasal margin weakly emarginate; posteroventral slope gentle, weakly concave (Fig. 5A View Figure 5 ). Abdominal segment III in dorsal view subtrapezoidal, strongly wider posteriorly, 1.18-1.31 × wider than long (DA3I, 118-131; Fig. 5B View Figure 5 ); lateral margins only feebly evenly convex; 1.59-1.62 × wider than petiole. Abdominal posttergite III subrectangular in lateral view, with almost vertical anterior face; distinctly larger in height than fused poststernite III (Fig. 5A View Figure 5 ). Abdominal segment IV in dorsal view 1.03-1.12 × wider than long (DA4I, 103-112), with strongly convex lateral margins (Fig. 6A View Figure 6 ). Putative glandular patch near posterior edge of abdominal poststernite IV feebly recognizable as oval pale area contrasted by little darker-colored proximate surrounding (black arrow in Fig. 6B View Figure 6 ; no specialized structure such as gland opening recognizable on the external sternal surface).

Setation and sculpture. Body setation relatively sparse. Anterolateral surfaces of cranium coarsely longitudinally rugose (Fig. 2A View Figure 2 ); other areas of cranium basically smooth except having sparse seta-bearing foveae; posterolateral surfaces very smooth with few setae and sculpturing (Fig. 3A View Figure 3 ). Frontal face of labrum reticulate (Fig. 4A View Figure 4 ). Proximal face of maxillary stipes mostly smooth. Dorsum of mesosoma and petiole smooth and shiny with sparse seta-bearing foveae; pronotal flange, lateral surfaces of mesosoma and petiole shiny but superficially reticulate-imbricate (Fig. 5A-C View Figure 5 ); propodeal declivity and anterior face of petiole smooth. Abdominal postsclerites III and IV smooth, except sparse seta-bearing foveae. Cinctus of abdominal segment IV almost smooth, with coarse short longitudinal ribs near its anterior margin (Fig. 6C View Figure 6 ). Presclerites of abdominal segment IV reticulate-imbricate. Abdominal tergites V-VI largely smooth with superficially imbricate anterior face. Abdominal tergite VII (pygidium) coarsely areolate-reticulate except superficially imbricate anterior face, armed with numerous stout chaetae arranged in two or three irregular oblique-longitudinal rows along each posterolateral margin (Fig. 6D View Figure 6 ).

Dealate queen. Largely similar to the worker except for some queen-specific features. Eyes and ocelli large and conspicuous (Fig. 7A, B View Figure 7 ); eyes circular with ~ 20 ommatidia at maximum diameter in lateral view; minimal distance between margins of median and lateral ocellus as long as major diameter of median ocellus; minimal distance between margins of lateral ocelli ~ 2 × major diameter of median ocellus. Mesosoma with fully developed flight sclerites and wing basal remnants (Fig. 7C View Figure 7 ); pronotum dorsolaterally coarsely foveolate-reticulate; notauli weakly present as coarse groove; parapsidal lines distinct; mesopleuron almost smooth; oblique mesopleural sulcus deep and conspicuous. Petiole in dorsal view almost as long as wide (DPI, 100-101); abdominal segment III in dorsal view 1.15-1.19 × wider than long (DA3I, 115-119); abdominal segment IV in dorsal view 1.10-1.12 × longer than wide (DA4I, 89-91). Putative glandular patch near posterior edge of abdominal poststernite IV feebly recognizable as in worker (black arrow in Fig. 7D View Figure 7 ).

Male. Unknown.

Etymology.

The specific epithet is named after the type locality, Ea So Nature Reserve: easo combined with the Latin feminine suffix - ana, adjective.

Habitat.

The collecting site of the type colony series is primarily covered with a relatively disturbed secondary evergreen forest. The collector (K. Eguchi) did not record the exact microhabitat and collecting situation of the colony fragment.

Differences from E. wroughtoni .

The worker of E. easoana is morphologically easily distinguished from the only other valid congener E. wroughtoni from southern Africa (see also the account of E. wroughtoni below) by the combination of following characteristics: i) frontal line distinct, extending a little beyond mid-length of cranium; ii) anterior (frontoclypeal) margins of torulo-posttorular complex not forming conspicuous lobes protruding over anterior clypeal margin in full-face view (anterior clypeal margin evenly weakly concave in full-face view); iii) mandibles when closed in full-face view forming only a little space between anterior clypeal margin and mandibles (basal angles nearly reaching center line of cranium when mandibles closed); iv) promesonotal suture faint and inconspicuous; v) abdominal segment III in dorsal view distinctly wider than long, with lateral margins only feebly convex.

Morphological remarks.

The morphology of workers of E. easoana is generally consistent with the concept of Eburopone in Borowiec (2016), except for the number of labial palpomeres. Borowiec (2016) stated that both the maxillary and labial palps of Eburopone are bi-merous in workers. However, E. easoana has a bi-merous maxillary and tri-merous labial palps (Fig. 4C, D View Figure 4 ), indicating the inter-specific variation of the character within the genus. According to Borowiec (2016), in dorylines, the labial palps of workers have, as a rule, fewer palpomeres than the maxillary palps of the same individual, except for the New World army ants and Acanthostichus Mayr, 1887. Therefore, E. easoana represents a new exception against this rule. The known palp formula of Eburopone worker is updated to 2, 2 or 2, 3.

Borowiec (2016) described the condition of pronotomesopleural junction in Eburopone workers "pronotomesopleural suture visible as groove but not unfused". However, the pronotomesopleural junction of the E. easoana workers can be interpretable as unfused in terms of the absence of sclerotized fusion, since the “groove” between the two sclerites seems membranous (Fig. 5A, C View Figure 5 ). Based on examination of the specimen images on AntWeb, the pronotomesopleural junction of E. wroughtoni also seems to be in the same condition.