Syscia arcodorsa, Du & Xu & Chen, 2024

Du, Congcong, Xu, Zhenghui & Chen, Zhilin, 2024, Taxonomic account of the ant genus Syscia Roger, 1816 (Hymenoptera, Formicidae) from Asia, with descriptions of two new species from China, European Journal of Taxonomy 930, pp. 157-181 : 161-164

Syscia arcodorsa sp. nov.

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Fig. 2 , Table 1

Diagnosis

Body color brown with antennae and legs yellowish brown. Head in full-face view oval, distinctly longer than broad; antennae 11-segmented. Mesosoma in dorsal view subrectangular; in lateral view, dorsal outline distinctly convex. Petiole in dorsal view subrectangular, slightly longer than broad; in lateral view, petiolar node (excluding sternite) trapezoidal, slightly longer than high; subpetiolar process in lateral view subtriangle. Postpetiole in lateral view slightly higher than long, sternite anteroventrally produced as a blunt angle directed downward and forward.

Etymology

The specific epithet refers to the dorsal outline of the arched mesosoma in lateral view.

Type material

Holotype (worker) CHINA • Guangxi, Guilin City, Longshen Town, Huaping Village in the Huaping National Nature Reserve ; 25.626944° N, 109.183333° E; 503.50 m a.s.l.; 22 Jul. 2021; Zhilin Chen leg.; No. GXNU210848; GXNU: GXNU210848 .

Paratypes (workers) CHINA • 1 worker; same collection data as for holotype; GXNU: GXNU210848-1 • 1 worker; same collection data as for holotype; SWFU: GXNU210848-2 • 1 worker; same collection data as for holotype; IZCAS: GXNU210848-3 .

Description

MEASUREMENTS AND INDICES. Holotype worker: BL 3.70, HL 0.63, HW 0.44, CI 70, SL 0.40, SI 91, MW 0.30, ML 0.70, PL 0.32, PH 0.30, PW 0.30, PI1 107, PI2 94, PPL 0.48, PPH 0.55, PPW 0.46, PPI1 86, PPI2 96, WI 152. Paratype workers: BL 3.61–3.73, HL 0.62–0.69, HW 0.43–0.49, CI 69–71, SL 0.36–0.43, SI 80–100, MW 0.33–0.35, ML 0.75–0.83, PL 0.27–0.33, PH 0.25–0.33, PW 0.25–0.33, PI1 100–108, PI2 96–100, PPL 0.44–0.45, PPH 0.42–0.45, PPW 0.40–0.50, PPI1 97–108, PPI2 89–100.00, WI 133–175 (n = 3) (individual measurements see Table 1 ).

Worker

HEAD. Antennae with 11 segments; apical antennal segment (XI) conspicuously enlarged, much broader than and longer than two preceding segments (IX–X) combined; scape short, not reaching mid-length of head when folded back ( Fig. 2A ). Head in full-face view oval, distinctly longer than broad, lateral margins convex, middle part of posterior margin slightly concave, with posterolateral corners rounded obviously ( Fig. 2A ). Frontal carinae short and narrow, not reaching to middle of head, with anterior half sharply elevated and posterior half low and vestigial in profile. Clypeus short, anterior margin almost straight. Eyes and ocelli completely absent ( Fig. 2A ). Mandibles triangular; masticatory margin serrated, without distinct teeth.

MESOSOMA. In dorsal view, rather robust, subrectangular, with lateral margins slightly convex, anterior margin convex, and posterior margin slightly concave ( Fig. 2B ); in lateral view, dorsal outline strongly convex; promesonotal suture and metanotal groove absent; mesopleuron demarcated from pronotum by distinct suture, but not demarcated from mesonotum and metapleuron; mesopleuron also not differentiated from metapleuron ( Fig. 2C ). Propodeal declivity feebly convex, encircled with distinct thin rim ( Fig. 2C ).

METASOMA. In dorsal view, petiole subrectangular, slightly longer than broad, lateral margins slightly convex ( Fig. 2B ); in lateral view, petiolar node (excluding sternite) trapezoidal with slightly convex dorsal outline, slightly longer than high, with bilateral edge sloped slightly ( Fig. 2C ). Subpetiolar process in lateral view subtriangle, with ventral outline concave ( Fig. 2C ). Postpetiole in dorsal view clearly larger than petiole, subtrapezoid, anterior margin slightly concave and shorter than posterior margin, lateral margins apparently convex ( Fig. 2B ); in lateral view, postpetiole slightly higher than long; dorsal outline slightly convex; postpetiolar sternite in lateral view low, with ventral margin slightly convex, anteroventrally produced as blunt angle directed downward and forward ( Fig. 2C ). Abdominal tergite IV (second gastral tergite) in dorsal view elongate, subrectangular with lateral margins convex, anterior margin obviously concave, and lateral margins slightly convex ( Fig. 2B ).

SCULPTURE. Entire body with numerous, relatively small, closely-spaced foveolae ( Fig. 2 ). Antennal scape, outer surface of mandibles, and legs with fine dense micropunctures ( Fig. 2A–C ).

PILOSITY. Body entirely covered with long and short decumbent, sub-erect, and erect hairs.

COLORATION. Body brown. Antennae and legs yellowish brown ( Fig. 2 ).

Distribution

China (Guangxi).

Habitat

The nest of Syscia arcodorsa sp. nov. was found in the Huaping National Nature Reserve, Guangxi, China. The sampled site is located in the evergreen broad-leaf forest, in the soil surface under the falling leaves near a flowing mountain stream.

Recognition

Syscia arcodorsa sp. nov. is similar to S. reticularis , because both of them have oval heads in full-face view. But it can be distinguished from the latter by the body covered with punctures or shallow fovea; however, the latter body is entirely reticulate, with deep bottoms.

This new species is also similar to an Indian species, S. indica , in general appearance of the workers with 11-segmented antennae. However, S. arcodorsa sp. nov. can be distinguished from the latter by the following characteristics: 1) head in full-face view oval, with posterolateral corners of head rounded obviously in S. arcodorsa (but head in full-face view rectangular, with posterolateral corners of head angular obtusely in S. indica ); 2) dorsal outline of mesosoma in lateral view curved or arched in S. arcodorsa (but almost straight in S. indica ); 3) declivity of propodeum in lateral view almost convex in S. arcodorsa (but slightly concave in S. indica ).

Figures

Fig. 2. Syscia arcodorsa sp. nov., holotype, worker (GXNU210848). A. Head in full-face view. B. Body in dorsal view. C. Body in lateral view (imaged by Zhilin Chen).