Aphaenogaster gamagumayaa Naka & Maruyama, 2018

Naka, Takeru & Maruyama, Munetoshi, 2018, Aphaenogaster gamagumayaa sp. nov.: the first troglobiotic ant from Japan (Hymenoptera: Formicidae: Myrmicinae), Zootaxa 4450 (1), pp. 135-141 : 136-139

Aphaenogaster gamagumayaa Naka & Maruyama , sp. nov.

Type series. Holotype, worker, Nakagusuku-son, Okinawa-jima, Japan, 10 IX 2017, T. Naka ( The Institute of Tropical Agriculture , Kyushu University = KUM, no MMANT001 ) . Paratypes, 7 workers, the same locality, collected between 31 VIII - 10 IX 2017 (5 in KUM, nos. MMANT002-006 ; 2 in MCZC = Museum of Comparative Zoology , Harvard University, Cambridge, MA, USA, nos. MMANT007,008 ) .

Diagnosis. This species is distinguished from the other East Asian species by having the most elongate body, the longest antennae and legs, and the most reduced eyes. Among the Japanese species, it is most similar to A. irrigua Watanabe & Yamane, 1999 described from Ryukyu Archipelago. It differs from A. irrigua in lighter color, smaller eyes (EL 0.19 x TmL vs. 0.38 x TmL), basal margin of mandible with weaker serration, and scapes more elongate and slim (SL 2.28 x HW vs. 1.53 x HW).

Measurements. Workers (n = 6). HL, 1.499 ± 0.047 (1.439–1.566); HW, 1.118 ± 0.030 (1.073–1.152); TmL, 0.790±0.038 (0.743–0.843); GL, 0.808±0.027 (0.778–0.856); SL, 2.429±0.053 (2.350–2.509); EL, 0.143±0.006 (0.134–0.149); EW, 0.119±0.005 (0.114–0.128); ML, 2.563±0.074 (2.463–2.659); PSL, 0.363±0.017 (0.348– 0.388); SDL, 0.252±0.010 (0.242–0.270); HTL, 2.121±0.047 (2.046–2.176); PL, 0.753±0.026 (0.702–0.769); PPL, 0.480±0.017 (0.465–0.513); PH, 0.389±0.008 (0.380–0.399); PPH, 0.356±0.034 (0.330–0.423); PNW, 0.748±0.022 (0.713-0.775); PW, 0.271±0.009 (0.260–0.283); PPW, 0.327±0.007 (0.317–0.338).

Description. Body ( Figs. 1–4 ) almost entirely yellowish. Head and mesosoma yellow, but mandibles and antennae darker, and base of head and anterior area of prothorax brown; legs light yellow but bases of femora, tibiae and tarsi darker. Gaster light yellow, but basal constriction brown, and posterior 1/2 slightly darker.

Head ( Figs. 2, 3 ) oval, without basal constriction or neck. Anterior margin of clypeus with weak transverse wrinkles and shallowly concave. Eyes very small, 0.19 times as long as length of tempora. Scapes elongate and slim, 2.28 times as long as width of head, at base 1.7 times as wide as at apex, gradually widened, straight, only apex slightly bent down with slight preapical constriction. Surface of scape shiny, uniformly covered with short and sparse adherent setae. Scape straight, only apex slightly bent down with shallow preapical constriction. Funicle elongate and thin, 1.38 times as long as scape, first funicular segment elongate, 3.17 times as long as wide at apex, 1.74 times as long as second segment, relative lengths of segments, 100:57:68:75:76:76:92:150:145:143:213, apical segment 3.1 times as wide as first segment. Pronotum ( Figs.1, 4 ) elongate, 1.37 times as long as wide, regularly convex in profile. Propodeum ( Figs. 1, 4 ) almost as long as wide, propodeal spines short, needle-like, obliquely directed upwards. Petiole (Fig. 1,4) elongate with long peduncle, its anterior face deeply concave, node globular and strongly convex. Ventral margin of petiole with low, short carina around middle. In dorsal view, petiole gently widened postriorly before petiolar node. Postpetiole ( Figs. 1, 4 ) short, 0.68 times as long as petiole, in profile regularly rounded, its node slightly lower than petiole. In dorsal view postpetiole 1.5 times as long as wide with regularly rounded sides.

Mandible ( Fig. 3 ) elongate, with outer edge straight, dorsal surface with distinct striation, inner margin with 7 or 8 small teeth. Lateral portion of clypeus ( Fig. 3 ) with 2–3 thin oblique rugae, central part without sculpture, shiny. Frontal carinae short, not extending to line connecting anterior margin of eyes, subparallel; interantennal area deeply impressed, smooth and shiny, frontal triangle shiny, with a few, shallow longitudinal wrinkles. Anterior portion of frons with thin longitudinal rugae, mesal area between eyes glabrous and shiny, posterior portion around vertex without rugae but with distinct microreticulation ( Fig. 3 ). Pronotum ( Figs. 1, 4 ) with microreticulation, but with smooth areas postero-laterally, with 8 short setae. Top of mesonotum ( Figs. 1, 4 ) covered with strong longitudinal rugae; mesopleuron with distinct granulate sculpture, matte. Propodeum ( Figs. 1, 4 ) with slightly granulate sculpture, below spiracles with two short, thin, longitudinal rugae with distinct transverse wrinkles, and dorsal surface of both mesonotum and propodeum appears slightly matte. Entire petiole and postpetiole covered with fine microreticulation, without rugae. appearing slightly matte, covered with several sparse setae. Gaster ( Fig. 1 ) smooth, shiny, without microreticulation except in basal area, tergites with sparse, suberect setae much shorter than propodeal spines. Legs ( Fig. 1 ) very long, hind femora 1.13 times as long as mesosoma, hind tibiae 0.77 times as long as hind femora, hind tarsi 1.19 times as long as hind femora. Surface of legs shiny, fore tarsi only on ventral surface covered with very short, appressed pubescence; femora and mid- and hind tibiae completely without pubescence.

Queens and males are unknown.

Etymology. The specific epithet is a Ryukyuan dialect “ gamagumayaa ” (= cave-dwelling hermit), referring to the habitat of the new species.

Biological notes. The type series of Aphaenogaster gamagumayaa is based on workers probably from a single nest, collected in a limestone cave on the island of Okinawa. All specimens were found in a guano hall ( Fig. 5 ), an area of approximately 25 m 2 (2–3 m in height), approximately 20 m from the cave entrance. The hall is completely dark, and during the study period (August to October 2017), it was consistently cooler (<25°C during the day) than the exterior of the cave (28–32°C). The cave contains no pools or streams but is generally wet, and the substrate is clay soil.

The ants were moving around an approximately 4-m2 area in which there were many small holes ( Fig. 6 ) and cracks in the cave floor. Ants were observed entering these holes. Although one of the authors, TN, did not dig into the holes, they were surmised to be associated with a core part of the nest. TN observed a maximum of 12 individual workers, most likely nest mates; no aggression was seen between them. Most of them were solitary foragers and observed on the cave floor or on the lower part of the cave wall. However, on one occasion two ants were observed walking together ( Fig. 7 ) for some time. On two occasions ants were seen carrying balls of guano into a hole ( Fig. 8 ). Another individual was observed carrying a small white object that did not appear to be guano. Upon perceiving human movement, the ants stopped moving and hid. While motionless, they waved their antennae, most likely to assess the situation. Gaster bending behavior, which is often observed in other Aphaenogaster species ( Terayama et al. 2014), has not been observed in A. gamagumayaa .

Figures

FIGURES 1–4. holotype worker of Aphaenogaster gamagumayaa sp. nov. 1) whole body in lateral view; 2) head; 3) head capsule; 4) mesosoma and fore segments of abdomen. Scales= 1.0 mm.

FIGURES 5–8. habitat photos of Aphaenogaster gamagumayaa sp. nov. 5) guano hall where the type series found; 6) the nest entrance; 7) two workers walking together; 8) worker carrying a guano ball.