Syscia yekzoeae Yamane et Mizuno, 2024

Syscia yekzoeae Yamane et Mizuno View in CoL , sp. nov.

http://zoobank.org/ 86921D8F-D0C4-4B4B-9FA7- DD76AE4896DF

Fig. 4A–D View Fig , 5A–D View Fig , 6A–D View Fig

Type material. Holotype: worker, East Malaysia (Borneo), Sabah, Papar, Hutan Lipur , Kawang FR, 15.xi.2023, Sk. Yamane leg., SB23-SKY-04 (24 SKYRM10 ; ITBC) . Paratypes: 1 queen, 2 workers & 2 males, same locality & date, Sk. Yamane / R. Mizuno leg., SB23-SKY-04 & RM772 (24SKYRM-11–15) .

Worker description. Diagnosis: Body dark reddish brown (with naked eyes looking almost black), large (3.6–4.1 mm in total length; 0.75–0.80 in head width), entirely covered with dense, coarse punctation. Parafrontal ridge with conspicuous process in anterior portion. Antenna with 9 flagellomeres (11 antennomeres). Propodeal declivity dorsolaterally with pair of short carinae. Petiole as broad as or slightly broader than long; postpetiole broader than long.

Measurements (n=3): TL 3.6–4.1, HW 0.75–0.80, HL 0.90–0.93, SL 0.60–0.63, PrW 0.57–0.62, PtW 0.49–0.52, PtL 0.47–0.52, PtH 0.47–0.49, PptW 0.61–0.68, PptL 0.57–0.62, PptH 0.45–0.46, GIW 0.93–1.03, G1L 0.94–1.01. CI 83.3–86.0, SI 77.9– 80.0, G1I 99.0–104.

Full description. Head in full-face view longer than broad, with very shallowly convex lateral margin, broadly emarginate posterior margin, and roundly angled posterolateral corner ( Fig. 4C View Fig ). Frontal carinae raised high, very close to each other, diverging anteriad; parafrontal ridge thick and well developed, with distinct process in anterior portion ( Fig. 4C View Fig , arrow 1); anteriorlydirected small process present in front of each antennal socket (arrow 2). Clypeus short, much broader than long, with concave disc, and broadly and weakly convex anterior and posterior margins. Eye absent. Mandible in dorsal view subtriangular; its masticatory margin evenly and shallowly concave, edentate; basal triangular area distinctly lower than main part of mandible; apex not sharply pointed. Antenna with 9 flagellomeres (11 antennomeres); scape when laid back slightly surpassing mid-length of head, broadened apicad, outwardly curved in apical one third; venter of scape deeply excavated in apical two-fifths; the excavation flanked by high lateral carinae; pedicel small, as long as broad; flagellomeres 1– VI (antennomeres III – VIII) bead-like, each broader than long; apical flagellomere very large, much longer than two preceding ones combined; club indistinct. Mesosoma in dorsal view narrower but longer than head; pro-mesonotal suture faint; metanotal groove completely absent; posterodorsal margin of propodeum with pair of short carinae that look like propodeal spines. Mesosoma in profile view with shallowly convex dorsal outline; pronotum separated from mesopleuron with deep suture, with anteroventral corner angulate; mesopleuron demarcated from metapleuron with faint line; metapleuron fused with lateral face of propodeum; metapleural gland orifice with oblong opening and ventral wall, without peripheral hairs; propodeal spiracle very small, smaller than nearby punctures, located low on lateral face far from posterior margin of declivity; propodeal lobe round. Propodeum in posterior view with pair of upper lateral carinae that are rather high; faint carina present (can be obsolete) between them; declivity with blunt longitudinal median keel in its lower part. All femora longer than tibiae; forebasitarsus in profile view broader basally than apically; hind basitarsus in profile view broadened apicad. Petiole slightly broader than long, with anterior and posterior margin straight and lateral margin shallowly convex; postpetiole broader than long, broadened posteriad, with almost straight anterior and posterior margins. With waist in profile view, petiolar node (tergite) longer than high; sternite distinctly demarcated from node; subpetiolar process subtriangular with anterior slope longer than posterior slope; postpetiole higher than long with convex dorsal and ventral outlines; its anteroventral margin round; sternite clearly separated from tergite by deep suture ( Fig. 4D View Fig ). With gaster in dorsal view, tergite I nearly as long as broad, with broadly concave anterior margin and almost straight posterior margin; lateral margin roundly convex; presclerite distinctly constricted around border of tergite and sternite ( Fig. 4C View Fig , arrow); cinctus dorsally cross-ribbed, forming chain of elongate punctures ( Fig. 4D View Fig , cinc), but ventrally reduced; other gastral tergites combined shorter than tergite I.

Almost entire body except for appendages densely covered with coarse punctures, with interspaces smooth and shiny.Area between frontal carinae and posterior half of clypeus smooth and shiny; anterior half of clypeus minutely sculptured and matte. Mandible strongly punctate with apical area, narrow area along masticatory margin and basal triangular corner smooth and shiny. Antennal scape with dense small punctures; pedicel with dense minute punctures and matte; flagellomeres I– VIII basally minutely punctate and mat, apically smooth and shiny; punctate area more extensive in flagellomeres VI – VIII; apical flagellomere entirely covered with superficial ill-defined punctuation and rather shiny. Coxae, femora and tibiae of all legs anteriorly with ill-defined irregular punctuation; tarsi with finer punctuation. Pretergite and presternite of gastral segment I with fine transverse striation.

Entire body dorsally with suberect/ decumbent hairs of varying length. Lateral margin of head in full-face view with short decumbent hairs. Dorsal and lateral faces of mandible with erect/suberect hairs of varying length. Antennal scape covered with dense pubescence and with a few long suberect hairs; pedicel and flagellomeres I– VI with short erect/suberect hairs; apical three flagellomeres covered with much shorter erect hairs and sparsely with fewer slightly longer hairs. Metapleural gland orifice with a few peripheral hairs partly covering the orifice. All legs covered with near-appressed short hairs and longer suberect/ decumbent hairs of varying length. Subpetiolar process ventrally with several erect hairs; sternite of postpetiole ventrally with sparse suberect hairs; anteroventral margin of the sternite with dense short hairs. Gastral sternites with pilosity slightly sparser than on tergites.

Body entirely dark reddish brown (with naked eyes almost black). Scape and apical flagellomere, and all legs much paler than body proper.

Queen description. Measurements (n=1). HW 0.77, HL 0.92, SL 0.61, EW 0.10, EL 0.13, PrW 0.70, PtW 0.54, PtL 0.48, PtH 0.51, PptW 0.69, PptL 0.58, PptH 0.48, G1 W 1.12, G1L 1.06, FwL 0.52, HwL 0.40. CI 83.7, SI 79.2, G1I 106.0.

Description. Similar to worker in size, structure and sculpture except for caste-specific characters mainly seen in head and mesosoma ( Fig. 5A, B View Fig ). Eye located at midlength of cranium, hemispherical, distinctly raised above surrounding cranial surface, with ca. 10 ommatidia that are ill defined; ocelli arranged in flat triangle; anterior ocellus larger than posterior ocellus. With mesosoma in dorsal view ( Fig. 5A View Fig ), mesoscutum as long as pronotum, longer than mesoscutellum, anteriorly roundly convex, demarcated from pronotum by distinct suture; scuto-scutellar suture straight; metanotum short (‘narrow’), poorly defined; propodeum as long as mesoscutellum, deeply emarginate posteriorly. With mesosoma in profile view ( Fig. 5B View Fig ), pronoto-mesopleural suture complete; mesopleuron not divided into upper and lower sections, poorly demarcated from metapleuron; metapleuron and lateral face of propodeum completely fused. Wings present, but vestigial ( Fig. 5D View Fig ); forewing with three longitudinal veinlike thickenings that are blackish, without closed cell. Body entirely orangish brown, with apical flagellomere of antenna and legs more yellowish.

Male description. Measurements (n=2). HW 0.72–0.73 (HWe 0.84–0.90), HL 0.72–0.77, SL 0.33, PrW 0.78–0.82, PtW 0.38–0.39, PtL 0.33–0.35, PtH 0.37–0.42, PptW 0.46–0.48, PptL 0.44–0.47, PptH 0.50–0.53, G1 W 0.88 –0.93, G1L 0.84–0.86, FwL 2.70–2.80, HwL 1.14–1.17. CI 95.0–100.0, SI 45.2–45.8, G1I 105.8–108.1.

Description. Head in full-face view as long as broad, but broader than long when including eyes (CIe: 116.7-116.9); posterior margin broadly convex with median emargination ( Fig. 6C View Fig ). Frontal carinae short, convergent posteriad; parafrontal ridge essentially absent; antennal scrobe small with its posterior margin located at level of posterior end of frontal carina. Clypeus clearly separated from frons by transverse ridge, with almost vertical posterior portion; anterior clypeal margin convex. Mandible subtriangular, with sharply pointed apex; masticatory margin serrate or provided with minute denticles; basal margin straight and entire.Antenna with 10 flagellomeres (12 antennomeres); scape shorter than eye width, distally widened; pedicel small, as long as flagellomere I; flagellomeres each longer than broad, getting longer towards apical flagellomere; apical flagellomere 2.4 times as long as broad. Eye large, distinctly breaking lateral margin of head; inner eye margins diverging posteriad; ocelli complete, arranged in flat triangle; distance between anterior and posterior ocelli less than diameter of ocellus; distance between posterior ocellus and eye 1.6 times as long as that between posterior ocelli. With head in profile view, occipital carina not reaching mandibular base, distinctly visible for 2/3 length of temple+gena, not forming broad flange. Mesosoma in dorsal view ( Fig. 6A View Fig ; wings removed) broadest at forewing bases ( Fig. 6A View Fig , fwb); pronotum short, with anterolateral corner round; mesoscutum much broader than pronotum, anteriorly broadly convex, with V-shaped notauli ( Fig. 6A View Fig , ntl) and weak parapsidal line that ends at posterior end of notauli; mesoscutellum separated from mesoscutum with ‘broad’ and deep furrow; its width nearly same as distance between starting points of parapsidal lines; metanotum short (‘narrow’ band); propodeum short, margined posteriorly with transverse carina. With mesosoma in profile view ( Fig. 6B View Fig ), pronotum anteriorly steeply sloping; mesonotum distinctly higher than pronotum, metanotum and propodeum; pronotum dorsally very short, with its lateral face extensively concave; mesopleuron separated from pronotum with deep furrow, divided into upper and lower sections with deep furrow; its upper section demarcated from metapleuron, but lower section fused with the latter; lateral face of propodeum demarcated from metapleuron with vague furrow; propodeum without posterior spine; declivity steep, margined laterally and dorsally with continuous carina. Petiole in dorsal view broader than long, with lateral margin weakly convex; postpetiole broader than petiole, as long as broad, distinctly narrowed anteriad. With waist in profile view, petiole globular, with node as long as high; subpetiolar process triangular ( Fig. 6B View Fig , sptp); postpetiole with tergal and sternal portions almost of same height; sternum anteriorly distinctly carinate. Gastral tergite I in dorsal view slightly broader than long, laterally convex; cinctus throughout cross-ribbed; presclerites transversely striate. Wings fully developed; forewing with large pterostigma and reduced venation ( Fig. 6C View Fig ).

Head and mesosoma extensively and densely punctate or punctoreticulate; punctation on waist much sparser; gastral tergite I and sternite I essentially smooth; subsequent tergites and sternites densely with medium-sized punctures. Antenna with dense punctures and matte; coxae, femora and tibiae of all legs with irregular sculpture and weakly shiny; tarsi densely micropunctate and matte.

Dorsa of head, mesosoma, waist and gaster with decumbent to erect hairs of varying length. Venter of petiole lacking erect hairs, while that of postpetiole with erect hairs.Antennal scape with a few long erect hairs; pedicel and flagellum with much shorter hairs that are very dense. All legs with fine decumbent/appressed hairs and much longer suberect/erect hairs. Body entirely blackish, with mandible and tarsi of all legs brownish.

Remarks. In the worker caste Syscia yekzoeae sp. nov. is the largest among the Sundaland congeners, and comparable to the New World S. grandis Longino et Branstetter, 2021 among the named species. Syscia yekzoeae sp. nov. is very similar in coloration, structure and sculpture to S. reticularis Jaitrong et al. 2020 except in body size (3.7–4.1 mm in the new species vs. 2.4–3.0 mm in the latter in total body length; 0.75–0.80 mm vs. 0.46–0.50 mm in head width). However, it is also distinguished from S. reticularis in the following details: 1) head relatively broader, with lateral margin nearly straight (head distinctly longer than broad, with lateral margin convex in the latter), 2) parafrontal ridge with anterior process isolated from its main part (isolated process absent in the latter); 3) flagellomeres I–III (antennomeres III-V) bead-like, each longer than half length of pedicel (very short, not bead-like, and each much shorter than half length of pedicel in the latter); 4) propodeal declivity with pair of dorsolateral short carinae (carinae absent or obsolete in the latter); 5) gastral tergite I almost as long as broad with width/ length ratio (G1I) 0.92–1.01 (much longer than broad, with G1I 0.80–0.83 in the latter).

Biological note. The queen is brachypterous, with seemingly non-functional wings. Brachypterous queens are also known in some New World species such as S. amblyogyne Longino et Branstetter, 2021 , S. augustae (Wheeler 1902) , etc. Among the Old World species, one of the Thai species, S. chaladthanyakiji Jaitrong et al., 2020 , may be fully winged (a dealate queen is known: Jaitrong et al., 2020), while the Japanese species S. humicola Ogata, 1983 has ergatoid queens that are variable in eye size and the number of ocelli (none or one) ( Ogata 1983). The two queens of the present new species examined are orangish brown in boy color, unlike the worker and male that are dark reddish brown or blackish. This condition might reflect the age of these queens, since teneral adult ants are generally much paler than matured ones. Although their cuticle was fully sclerotized, they can be teneral adults. One dissected queen had eight ovarioles (4 in each ovary) and a worker had two (1 in each). The queen’s spermatheca was empty and neither developing oocyte nor yellow body accumulation was found.

The type series represented part of a colony. Six workers, two queens and a male were collected from under rotting wood and in soil; four workers were reared for behavioral observation and obtaining more specimens. During the colony rearing for six months (from collection date to 9 May 2024), they produced 11 males that obviously emerged from unfertilized eggs laid by workers. They went through four entire phasic reproductive cycle as suggested in a congeneric species S. humicola ( Masuko 2006) and known in some other non-army ant dorylines (e.g., Ravary & Jaisson 2002; Mizuno et al. 2021; Mizuno et al. 2023). Their pupae lacked a cocoon. They fed on provided ant brood ( Tetramorium bicarinatum larvae, n = 16; pupae, n = 16). On the other hand, young termites ( Incisitermes minor , 4 mm body length, n = 5) and small mealworms ( Tenebrio molitor , 4 mm body length, n = 4) were killed but never consumed by neither adults nor larvae. Therefore, this species is apparently an obligate ant predator like some other doryline ants for which prey are known ( Idogawa & Dobata 2018; Ito et al. 2018).

Etymology. The specific epithet, yekzoeae , is composed of the family name (Yek) and nickname (Zoe) of Dr. Yek Sze Huei of the Institute of Tropical Biology and Conservation, Malaysia Sabah University, to whom we are much indebted for her help in the field work.