Carebara lithophila Yamane, Sasaki et Hosokawa, 2025

Yamane, Sk., Sasaki, H. & Hosokawa, R., 2025, A NEW SPECIES OF THE ANT GENUS CAREBARA WESWOOD (FORMICIDAE, MYRMICINAE) FROM THE YAEYAMA ISLANDS, RYUKYUS ARCHIPELAGO, JAPAN, Far Eastern Entomologist 523, pp. 8-15 : 10-15

Carebara lithophila Yamane, Sasaki et Hosokawa , sp. n.

https://zoobank.org/NomenclaturalActs/ E31139EA-A4CA-41DD-89EC-0580F516040E

Figs 1–3 , 4 A,C,D

TYPE MATERIAL. Holotype – major worker, Agarisaki, Yonaguni-jima, Yaeyama Islands , Southern Ryukyus , Japan, 11.iii.2020, nest under big stone, Sk. Yamane leg. (deposited in SKYC, Kitakyushu Museum of Natural History and Human History , Japan) . Paratypes: all specimens originated from the same colony as the holotype. Four majors and nine minors collected by Sk. Yamane ( SKYC), 2 majors and 2 minors collected by F. Ito (Kagawa Univ.), and 5 majors and 6 minors collected by R. Hosokawa (Kagawa Univ.) .

WORKER DIAGNOSIS. Antenna with 7 flagellomeres (9 antennomeres); mandible with 5 teeth, of which basal tooth low and reduced. Major worker. Body 2.5–2.7 mm in total length; head width 0.58–0.59 mm. In profile view dorsal (‘anterior’) outline of head nearly straight. Vertex with pair of well-developed horns that are longer than their basal width and connected with complete carina. Eye small with one or two indistinct ommatidia. Anterior ocellus always present, but sometimes ill developed. Dorsum of mesosoma essentially smooth and shiny. Metapleural gland bulla entirely sculptured. Propodeal spine absent. Propodeal lobe with evenly curved posterior margin. Petiolar node in profile subtriangular, narrowed apicad. Minor worker. Body 0.85–1.00 mm in total length; head width 0.27–0.29 mm. Dorsum of head only superficially punctate and shiny. Obsolete eye generally present. Pronotum with scattered shallow punctation but smooth and shiny. Propodeal spine absent. Petiolar node in profile low, broadly rounded apically. Body yellow.

MAJOR WORKER DESCRIPTION ( Fig. 1 , 2 , Fig. 4A,C,D ). Measurements (in mm) and indices (n=5). TL 2.5–2.7, HW 0.58–0.59, HL 0.78–0.79, SL 0.28–0.30, PrW 0.38–0.40, PtW 0.17–0.18, PtL 0.09-1.00, PtH 0.20–0.22, PptW 0.19–0.20, PptL 0.11, PptH 0.13–0.14. CI 73.4–74.7, SI 47.5–51.7. Head in full-face view distinctly longer than broad, with deeply concave posterior margin, nearly parallel lateral margins and pair of well-developed horns near posterolateral corners of head; horns widely separated from each other (distance 0.35– 0.38 mm), connected with transverse carina, and tapered apicad. Anterior ocellus always present, but sometimes obsolete. Weak mid-cranial line (often obsolete) starting at anterior ocellus and reaching posterior end of unsculptured triangular area of frons behind clypeus. Frontal carina very short, extending slightly beyond level of posterior margin of torulus; frontal lobe broad; distance between frontal lobes subequal to lobe width. Clypeus roughly divided into sloping anterior disc + transverse lateral areas and posterior narrow area, the last being flanked by frontal carinae, and posteriorly not clearly demarcated from frons by suture; anterior disc roughly trapezoidal, almost flat, flanked by strong lateral carinae that are divergent apicad, anteriorly shallowly convex; anterior margin of the disc medially straight to shallowly concave. Mandible triangular, stout, with five teeth on masticatory margin; size of teeth decreasing from apical to basal tooth, the last being low and often obsolete. With head in profile view, dorsal (‘anterior’) outline almost flat and ventral (‘posterior’) outline more convex. Eye small, composed of one or two indistinct ommatidia, located distinctly anteriorly on gena at 1/3 length. Antenna with 7 flagellomeres (9 antennomeres) with basal segments of flagellum poorly differentiated; scape short, when laid straight back from its insertion not attaining midlength of cranium, in frontal view with its 2/5 very narrow and apical 3/5 broad and spindle-shaped; pedicel longer than preapical flagellomere; apical flagellomere very long but shorter than remaining flagellomeres combined, apically pointed.

With mesosoma in dorsal view, pronotum largest, round, with posterior margin broadly concave; promesonotal suture well defined; mesoscutum broader than long, narrower than pronotum, narrowed posteriad; mesoscutellum weakly differentiated from mesoscutum, narrower than the latter, transverse; metanotal groove sharply defined; propodeal dorsum slightly longer than broad, widened posteriad, triangularly concave; declivity laterally margined with carinae. With mesosoma in profile view, promesonotum forming single dome but divided into two sclerites by promesonotal suture, roundly convex, not smoothly continuous to dorsal outline of propodeum. Pronotum large, posteriorly with small dent at mid-height, ventrally carinate. Mesopleuron clearly demarcated from pronotum but vaguely from mesonotum. Metapleuron fused with propodeum in lower portion; metathoracic spiracle much smaller than propodeal spiracle, often obscure. Propodeum with almost straight dorsal outline; its posterolateral corner roundly angulate; posterior margin shallowly concave; propodeal lobe posteriorly evenly curved; spiracle located near center of lateral face of propodeum.

With waist in dorsal view, petiolar node broader than long, with straight anterior and convex lateral margins; postpetiole only slightly broader than petiole, broader than long, with straight anterior and convex lateral margins. With waist in profile view, petiole with distinct anterior peduncle; petiolar node with long steep anterior slope, short dorsum and gently sloping posterior slope that is longer than dorsum; ventral margin of petiole straight, without subpetiolar process. Postpetiole lower than petiole, with round apex and long posterior slope that is not clearly separated from dorsum.

Gaster voluminous, much larger than head, mesosoma and waist combined; cinctus on gastral tergite 1 (abdominal tergite 4) well defined, formed by chain of elongate punctures. Legs relatively short; femora basally distinctly flattened; tibiae each shorter than femora, widened apicad.

Body extensively shiny. Anterior half of head dorsum densely with longitudinal striation and matt; posterior half with punctation and rather shiny. Area in front of horn and around anterior ocellus irregularly sculptured. Areas in front of and behind carina connecting horns with fine irregular transverse striae; occiput smooth and shiny. Temple and gena smooth and shiny in posterior 2/3, but space between eye and mandibular base densely longitudinally striate (not reticulate) and matt. Venter of head extensively smooth except in anterolateral area striate. Anterior area of clypeus densely sculptured and matt. Mandible entirely smooth. Antenna and legs predominantly smooth and shiny. Dorsum of mesosoma largely smooth to very superficially sculptured and shiny; pronotum with irregular striation along its posterior margin. Lateral face of pronotum smooth, with median zone puncto-striate. Mesopleuron extensively smooth, but anteroventrally and posteriorly sculptured. Metapleuron and lateral face of propodeum extensively striate; metapleural gland bulla entirely sculptured. Dorsum of waist smooth; remaining parts sculptured. Gastral tergites and sternites essentially smooth and shiny, with sparse piligerous punctures; pretergite of gastral segment 1 minutely sculptured and matt. Antenna and legs predominantly smooth and shiny; coxae and trochanters irregularly sculptured.

Head dorsum with suberect hairs of variable length; with head in full-face view its lateral margin posteriorly with sparse long hairs, anteriorly without erect hairs; venter of head with relatively long appressed hairs and sparse erect hairs. Mandible with sparse minute hairs only, but several longer decumbent hairs present along masticatory margin. Clypeus essentially glabrous. Antenna covered with suberect hairs. Mesosomal dorsum with sparse erect/suberect hairs. Waist dorsally with long erect hairs. Dorsum of gastral tergite 1 with erect/suberect hairs of variable length; tergites 2–4 glabrous except for apical zones, which bear long erect hairs; sternite 1 with sparse erect hairs; sternites 2–4 with erect hairs only apically; apical tergite and sternite with erect hairs. Coxae with suberect hairs; femora basally with relatively short suberect hairs on ventral face; fore- and hindtibiae with nearappressed hairs on dorsal (outer) faces, and longer slanting hairs in apical 1/3 of ventral (inner) face; midtibia with longer, often slanting hairs on dorsal face; all tibiae with longer suberect hairs on apicoventral areas; tarsi covered with numerous suberect hairs. Body entirely yellowish brown; clypeus and mandible slightly darker.

MINOR WORKER DESCRIPTION ( Fig. 3 ). Measurements (in mm) and indices (n=5). TL 0.85–1.00, HW 0.27–0.29, HL 0.33–0.36, SL 0.18–0.20, PrW 0.18, PtW 0.08–0.09, PtL 0.05–0.07, PtH 0.09, PptW 0.09, PptL 0.07, PptH 0.07. CI 80.0–82.4, SI 64.3–67.9. Head in full-face view longer than broad, with posterior margin very shallowly emarginate, lateral margins parallel and posterolateral corner roundly angulate; occipital margin not carinate. With head in profile view, dorsal (‘anterior’) and ventral (‘posterior’) margins straight and almost parallel. Frontal carinae very short and parallel; frontal lobe small, only partly covering antennal socket. Clypeus composed of posterior small area flanked by frontal lobes and anterior large transverse area bridged by narrow median disc with posterior area, anteriorly shallowly convex, with anterior margin curved. Mandible elongate-triangular with five teeth; apical tooth largest and basal one very small. Eye very small, sometimes vestigial, located anterior to midlength of cranium. Antenna with 7 flagellomeres (9-antennomeres); scape when laid straight back from its insertion reaching midlength of cranium, with apical 3/5 distinctly widened and flattened: pedicel relatively large, only slightly shorter than flagellomeres 1-5 that are each very small and broader than long; preapical flagellomere globular, slightly longer than broad; apical flagellomere large, parallel-sided in basal half, then narrowed apicad.

Mesosoma in dorsal view much narrower than head, distinctly constricted at metanotal groove; promesonotal suture almost invisible; promesonotum slightly longer than broad, roundly convex laterally, distinctly narrowed posteriad to metanotal groove at which mesosoma is narrowest; propodeum slightly broader than long, laterally convex. With mesosoma in profile view, its dorsal outline rather straight but interrupted by metanotal groove; lateral face of pronotum large, round; mesopleuron demarcated from pronotum but not from mesonotum; metapleuron separated from mesopleuron with distinct furrow but fused with lateral face of propodeum to form single sclerite; propodeum posteriorly carinate. Legs short; hindtibia shorter than hindfemur, distinctly widened apicad.

With waist in dorsal view, petiolar node broader than long, with anterior margin straight and lateral margin convex; postpetiole node broader than long, with parallel anterior and posterior margins, and weakly convex lateral margin. With waist in profile view, petiole with distinct anterior peduncle; petiolar node low, globular, with broadly rounded apex; subpetiolar process absent; postpetiole much lower than petiole, with less convex apex. Gastral segment 1 occupying major part of gaster, with flat dorsal and convex ventral outlines; tergite 1 in dorsal view with deeply emarginate anterior margin and convex lateral margin.

Body extensively shiny. Almost entire dorsum of head covered with piligerous punctures of moderate density but shiny; frontal lobe rugosopunctate; lateral portion of anterior transverse area of clypeus longitudinally rugose. Lateral and ventral faces of head essentially smooth. Mandible essentially smooth with scattered punctures, shiny. Antenna extensively smooth with sparse punctation and shiny. Mesosoma essentially smooth, with sparse punctation and shiny; pronotal lobe (neck) sculptured but shiny; punctures on mesopleuron small and dense. Waist mostly smooth and shiny dorsally, but punctate laterally; postnodal area of petiole densely punctate and matt on both dorsal and lateral faces. Gaster essentially smooth and shiny. Legs smooth with superficial punctation and shiny.

Entire dorsum of body densely covered with short erect/suberect hairs and very sparse longer erect hairs, but gastral tergite 1 almost lacking long hairs. Anterior margin of clypeus with pair of long hairs straddling midpoint and 2–3 pairs of shorter hairs laterally. Antenna and legs covered with short suberect hairs.

COMPARATIVE NOTES. In the major worker, Carebara lithophila sp. nov. is separated from all the other Japanese congeners by the following combination of characteristics: 1) horns on vertex very large, longer than its basal width, widely separated from each other, and connected with complete transverse carina; 2) posterior half of head dorsum only sparsely punctate and shiny; 3) anterior ocellus present ( Fig. 2 ), 4) basal tooth of mandible low and apically blunt; 5) mesopleuron without suture separating it into upper and lower sections; 6) posterodorsal corner of propodeum roundly angulate ( Fig. 4C,D ); 7) petiolar node in profile subtriangular, narrowed apicad; 8) subpetiolar process absent. In the minor worker, the new species is easily separated from all the other Japanese congeners by the following combination of characteristics: 1) head dorsum with punctures, but smooth and shiny, 2) pronotal dorsum essentially smooth, scattered with shallow punctures, and shiny, 3) propodeal spine absent, 4) body yellow.

The new species seems most closely related to Carebara sakamotoi Terayama, Lin et Eguchi, 2012 from Taiwan. In the major worker it can be distinguished from the latter by 1) head in full-face view with almost parallel lateral margins (lateral margins weakly convex in sakamotoi ), 2) anterior ocellus present (absent in sakamotoi ), 3) space between mandibular base and eye (malar space) with strong longitudinal striae (striation more irregular and weaker in sakamotoi ), 4) posterodorsal area of ventral face of head smooth (ventral face of head largely weakly sculptured in sakamotoi ), 5) mesopleuron smooth and very shiny in its anterior 3/4 (more extensively sculptured in sakamotoi ), 6) metapleural gland bulla entirely sculptured (smooth in posterior half in sakamotoi ), 7) dorsal (outer) face of fore- and hind tibiae with short appressed to decumbent hairs (with longer suberect hairs in sakamotoi ) ( Fig. 4A vs. B), 8) with mesosoma in full-profile view, posterior corner of propodeum slightly angulate (rounded in sakamotoi ; note that the propodeal corner should be viewed exactly from the same direction, otherwise its shape looks very differently) ( Fig. 4C & D vs. E), 9) propodeal lobe with posterior margin evenly curved (posterior margin more irregular in shape in sakamotoi ) ( Fig. 4C & D vs. E). The last character is variable in the new species, and might be a poor marker. In the minor worker, the new species is very difficult to separate from C. sakamotoi . The hairs on the dorsal (outer) face of the foretibia tend to be short and somewhat decumbent in the new species (condition variable), while they are rather long and distinctly suberect in the latter. The propodeal lobe is generally higher (‘broader’) and with more smoothly curved posterior margin (but shape variable) in the new species, but it is lower (‘narrower’) and with irregular posterior margin. According to the original description of C. sakamotoi the minor worker lacks the eye ( Terayama et al., 2012), but in the two paratypes of C. sakamotoi examined this time an obsolete ommatidium is seen as in the new species; the head dorsum is said to be reticulate, but actually distinctly punctate as in the new species; the metanotal groove is said to be absent, but it can be seen in both dorsal and lateral views as in the new species.

Carebara lithophila sp. n. also resembles C. bihornata ( Xu, 2003) in having a pair of well-developed vertexal hornes that are connected with a complete transverse carina, and nearly straight dorsal (‘anterior’) outline of head when viewed in profile (see also Xu et al., 2024). However, the new species can be distinguished from the latter in the following combination of features in the major worker: 1) eye much smaller with only one or two illdefined facets (larger, with four facets in bihornata), 2) anterior ocellus always present (absent in bihornata), 3) petiole subtriangular, distinctly narrowed apicad (more globular in bihornata; see Fig. B on page 177 in Xu et al., 2024), 4) mesosomal pilosity sparser (rather dense in the latter). In the minor worker, C. bihornata seems to lack any sign of the eye, while in the new species the vestigial facet of the eye generally exists.

ETYMOLOGY. The specific epithet refers to the nesting site of the colony from which the type series was collected (‘litho-‘ means stone, and ‘-phila’ means favoring).

Figures

Fig. 1. Major worker of Carebara lithophila sp. n. A – habitus in profile, B – habitus in dorsal view, C: head in full-face view.

Fig. 2. Head of major worker of Carebara lithophila sp. n., showing anterior ocellus.

Fig. 3. Minor worker of Carebara lithophila sp. n. A – habitus in profile, B – habitus in dorsal view, C – head in full-face view.

Fig. 4. Pilosity on foretibia in major worker (A, B), and posterior margin of propodeum in profile view in major worker (C–E). A, C, D – Carebara lithophila sp. n.; B, E – C. sakamotoi.