Ectomomyrmex horni (Forel, 1913)

Ectomomyrmex horni (Forel, 1913) View in CoL , status resurrected

( Figs 3C View Fig , 5C View Fig , 7C View Fig , 8 View Fig )

Pachycondyla (Ectomomyrmex) horni Forel, 1913: 185 View in CoL ; TERAYAMA (2009): 105 (in key).

Ectomomyrmex javanus Mayr, 1867 View in CoL : YASUMATSU (1962): 94 ( E. horni View in CoL synonymyzed with E. javanus View in CoL ); ANTWIKI (2024) (syntype images of Pachycondyla horni View in CoL examined).

Ectatomma [sic!] horni : SANTSCHI (1937): 363 (recorded from

Kagoshima, Japan).

Ectomomyrmex sauteri Forel, 1912 View in CoL : ONOYAMA (1980: 196).

Pachycondyla javana View in CoL : BOLTON (1995): 306 ( P. horni as junior synonym of P. javana View in CoL ); YAMANE et al. (2010: 121).

Ectomomyrmex sp. B : TERAYAMA et al. (2014: 54); TERAYAMA (2021): 90

(Japanese name: Minamifuto-hariari).

Material examined. JAPAN: KYUSHU: Kagoshima-ken (mainland): aq, Ono-chô, Kagoshima-shi, 30.x.1990, T. Iwai; w, Kôrimoyo, Kagoshima-shi, 2.ix.1998, Sk. Yamane; aq·m, same loc., 20.ix.1999; w, Toso, Kagoshima-shi, 12.vii.2002, T. Akiyama; m, Tagayama-Kôen, Kagoshima-shi, 8.xi.2013; w, Kurokami, Sakurajima, 26.v.2021, Sk. Yamane; w, near Yôgan-Nagisa (Taishô lava), 10.viii.2022, Sk.Yamane; w, Okoga-shima, off Sakurajima, 19.v.2009, S. Onoda; w, Sata-misaki, Minamiôsumi-chô, 7.v.2022, nest in soil, Sk. Yamane ( JP 22-SKY-019). RYUKYU ISLANDS: Kagoshima-ken: AMAMI IS.: Amami-ôshima: w, Kinsakubaru (300 m alt.), 28.viii.2000, Sk. Yamane. Okinawa-ken: OKINAWA IS.: Okinawa-jima: w, 15.v.1991, H. Watanabe. Kume- -jima: w, Daruma-yama, 8.x.2021, Sk. Yamane leg. YAEYAMA IS.: Ishigaki-jima: m, Omoto-dake, 16.x.1981, K. Konishi; w, Tomino, 6.v.2018, N. Murayama. Taketomi-jima: dq, 24.vii.1987, Sk. Yamane. Iriomote-jima: m, Komi, 6.vi.1982, K.Ôhara; w,Amitori, 21.vii.1989, Y. Nishizono; m, Komi, 12.x.1987,A.Nagatomi;w.Ôtomi-rindô, 28.iv.1998, K. Eguchi; w, Ôhara, 16.iii.2004, Sk. Yamane; w, Uehara near Univ. Ryukyus Field Stn., 11.xi.2018, Sk.Yamane. OGASAWARA ISLANDS : Tokyo-to: Haha-jima: w, Sakaiga-take (310–410 m alt.), 12.vii.1990, H. Watanabe; w, Sekimon, 6.vi.1998, N. Kawakubo & K. Nakashima. TAIWAN: Taipei Hsien: w, Fushan (600–670 m alt.), 22–23.ix.1997, Sk. Yamane.

Description of worker (based on Japanese and Taiwanese specimens). Measurements (n = 5: samples from Kyushu mainland and the Ryukyus). TL: 6.0– 7.3 mm, HW: 1.56–1.74 mm, HL: 1.73–1.88 mm, EL: 0.20–0.24 mm, SL: 1.25–1.36 mm, PrW: 1.06–1.24 mm, PtW: 0.84–0.96 mm; CI: 91–94, SI: 75–80.

Head in full-face view slightly longer than broad, with posterior margin broadly concave, lateral margin convex and posterolateral corner roundly angled. Clypeus convex anteriad, with anterior margin medially concave and indented; median area without longitudinal keel. Eye large, 0.20–0.24 mm in major diameter, with ca. 10 ommatidia (range: 9–11) along longest axis, located lower on head; malar space slightly shorter than or subequal to major diameter of eye. With head in full-face view antennal scape barely reaches posterior margin of head, but fails to attain posterodorsal corner; eye barely breaking lateral margin of head. Mandible elongate-triangular, with 9–10 teeth of varying size on masticatory margin; large and small teeth often alternating but not always. With mesosoma in dorsal view pronotum narrower than head; promesonotal suture distinct; propodeum as broad as mesonotum with much narrower dorsum; metanotal groove obsolete. In profile view mesosoma with dorsal outline evenly convex; pronotum anteroventrally angled, not produced as prominence, with ventral furrow that continues anteriad to pronotal lobe; metapleuron sharply demarcated from mesopleuron but fused with lateral face of propodeum; propodeal declivity laterally distinctly margined throughout. Petiole subsquamiform, with short transverse dorsum that is vaguely defined, large outwardly curved anterior face, linear lateral face and weakly concave posterior face; sternite sharply demarcated from tergite with sulcus, anteriorly produced ventrad. Gastral tergite I anteriorly truncate; prora scale-like with anterior concavity; gastral constriction weak; cinctus absent.

Dorsum and lateral face of head very densely striate and matte or with weak luster; striae not regular throughout, often waving and branching, mixed with small punctures. Frontal lobe laterally with distinct smooth area. Clypeus with median portion just below frontal lobe longitudinally rugulose; on anterior slope of lateral portion rugulae slightly coarser; dorsolateral portion densely micropunctate; anteromedian concaved part nearly smooth. Mesosoma almost entirely sculptured. Pronotum transversely striate on anterior lobe, densely punctate on dorsum, densely and minutely punctostriate on lateral face. Mesonotum with dense longitudinal rugulae; lower section of mesopleuron rather coarsely rugose from front to rear; metanotum with similar rugae. Dorsum of propodeum with coarse irregular sculpture; lateral face with coarse rugae as in metapleuron; declivity transversely rugose.Anterior and posterior faces of petiole transversely rugose; dorsal face superficially sculptured and shiny. Anterior vertical face of gastral segment I smooth with minute punctures from which setae arise; gastral tergites and sternites covered with dense small punctures, rather shiny; presclerites of gastral segment II with minute transverse striae, shiny.

Dorsum of head densely covered with decumbent to suberect golden hairs; clypeus anteriorly with two pairs of long hairs; venter of head with sparse erect hairs. Mandible with scattered short appressed hairs mixed with longer suberect hairs on dorsum; ventral face bearing much longer hairs. Eye with sparse but conspicuous erect hairs. Antennal scape with a few or no erect hairs on leading edge. Mesosomal dorsum densely covered with short appressed hairs and sparser erect hairs; erect/suberect hairs on propodeal declivity generally shorter than those on mesosomal dorsum. Anterior and posterior faces of petiole densely covered with fine appressed hairs; hairs on dorsal face stronger and variable in length. All gastral tergites and sternites covered with soft appressed hairs and stronger long hairs. Coxae, femora and tibiae with dense pubescence; erect hairs sparse on ventral faces of coxae and femora, almost absent on tibiae except for apical area. Body entirely dark reddish brown to blackish brown; antennal flagellum slightly paler; legs brown.

Description of queen (based on Japanese specimens). Measurements (n = 2). TL: 7.0– 7.2 mm, HW: 1.73–1.80 mm, HL: 1.81–1.90 mm, EL: 0.31–0.33 mm, SL: 1.35–1.38 mm, PrW: 1.36–1.38 mm, PtW: 1.05–1.06 mm; CI: 95, SI: 76–78.

In structure, sculpture and coloration similar to the worker except for caste-specific structures. Fully winged. Eye much larger than in the worker, 0.31–0.33 mm in major diameter, with ca. 16 ommatida along longest axis of eye; malar space subequal to half major diameter of eye. Pronotum densely transversely punctostriate; mesoscutum densely longitudinally punctostriate. Scutoscutellar sulcus ‘broad’; coarse rugae running from front to rear, anteriorly defined by deep suture that continues anteriad along lateral margin of scutum. Anterior and posterior faces of petiole more strongly rugose than in worker; dorsum of petiole irregularly sculptured (almost smooth in worker). Antennal scape bearing sparse erect hairs on its leading edge. Hindwing with jugal lobe.

Description of male (based on Japanese specimens). Measurements (n = 5). TL: 5.5–6.4 mm, HW: 0.95–1.08 mm, HL: 0.93–1.03 mm, EL: 0.51–0.60 mm, SL: 0.16–0.21 mm, PrW: 1.15–1.39 mm, PtW: 0.50–0.64 mm; CI: 101–109, SI: 16–20.

Head slightly broader than long when excluding eyes, but much broader when including eyes (HWe: 1.08–1.21 mm). Clypeus broadly and slightly produced anteriad, with median portion of anterior margin almost straight. Distance between antennal insertions shorter than diameter of antennal scape. Eye large, composed of more than 50 ommatidia along longest axis of eye, with inner margin shallowly concave; its outer margin distinctly breaking lateral margin of head. Ocelli large, arranged in low triangle; distance between anterior and posterior ocelli shorter than ocellar diameter. Mandible reduced, in profile view spatulate, in dorsal view linear. Palpal formula: 6, 4. Thorax in dorsal view as broad as head; mesoscutum with profound notaulix that merges posteriorly into median sulcus that reaches posterior margin of scutum, and with weaker parapsidal line and strong parascutal carina; scutoscutellar sulcus deep with foveae on its bottom; mesoscutellum distinctly convex dorsally; metanotum ‘narrow’ band, posteriorly more sharply defined than anteriorly. Thorax in profile view with mesopleuron divided into upper and lower sections with deep and ‘broad’ sulcus whose bottom has foveolae; metapleuron demarcated from mesopleuron. Declivity of propodeum demarcated from dorsal and lateral faces, but dorsal face merging into lateral face. Petiole globular, in profile view rather thick, weakly tapered apicad, with broadly rounded apex. Gaster anteriorly not truncate; with gaster in profile view anterior slope roundly continuing to dorsum; prora scale-like; gastral constriction moderate; cinctus absent.

Entire body sculptured. Dorsum of head very densely puncto-striate; in median zone between anterior ocellus and clypeus sculpture weaker; clypeus superficially sculptured and shiny. Mesosoma entirely coarsely sculptured.Anterior face and sometimes upper half of lateral face of petiole densely and irregularly sculptured; remaining portion of petiole extensively smooth and shiny. Gastral tergites and sternites superficially and finely punctate and shiny; presclerites of gastral tergite II and sternite II minutely and transversely striate. Hindwing with jugal lobe.

Head and mesosoma with dense appressed/decumbent short hairs and longer suberect hairs. Antenna and legs covered with short appressed pubescence; coxae and femora sparsely covered with longer erect/suberect hairs. Dorsum and lateral face of petiole with many erect hairs of varying length; anterior and posterior faces with shorter slanting hairs. Body entirely dark reddish brown to blackish brown; antenna, mandible, coxae and femora brown; maxillary and labial palpi, tibiae and tarsi yellowish.

Distribution. Japan: Kyushu ( YAMANE et al. 2010), Amami Islands (Amami-ôshima) ( ABE 1977, YAMANE 2016), Okinawa Islands (Okinawa-jima, Henza-jima, Miyagi-jima, Tokashiki-jima, Kume-jima*) ( ONOYAMA 1976, TERAYAMA et al. 2014), Miyako Islands (Miyako- -jima, Irabu-jima, Shimoji-jima) ( TERAYAMA et al. 2014), Tarama Island (Tarama-jima) ( TERAYAMA et al. 2014), Yaeyama Islands (Ishigaki-jima, Taketomi-jima, Iriomote-jima, Hateruma-jima, Yonaguni-jima) (ABE 1974, TERAYAMA et al. 2014), Senkaku Islands (Uotsuri-jima) ( AZUMA 2002; TERAYAMA et al. 2009, 2014), Ogasawara Islands (Haha-jima) ( KATO 1992, OHBAYASHI et al. 2003). Taiwan (FOREL 1913, TERAYAMA 2009).

Remarks. Ectomomyrmex horni was described by FOREL (1913) as a species of Pachycondyla F. Smith, 1858 closely related to Pachycondyla (Ectomomyrmex) sauteri Forel, 1912 (junior primary homonym of Pachycondyla sauteri Wheeler, 1906 ) based on the worker and queen castes. FOREL (1913) mentioned that in the worker this species is separated from the latter mainly by a larger body (7.0– 7.5 mm; 6.5 mm in E. sauteri ) and the anteroventral corner of the pronotum bluntly angulate (produced as a tooth in E. sauteri ). Another related species, E. denticeps Wheeler, 1929 , was described by WHEELER (1929); this is very peculiar in having a distinct tooth at the posterolateral corner of the head ( WHEELER 1929: 33, fig. 2). However, YASUMATSU (1962) mentioned that another specimen in the MCZ (not cited by Wheeler) displays a different condition of this character, suggesting that the holotype shows an anomaly.

YASUMATSU (1962) assigned all the above forms to Ectomomyrmex , synonymized E. horni and E. denticeps with E. javanus Mayr, 1867 , and suspected that E. sauteri is also a junior synonym of E. javanus (type locality: Java). Although ONOYAMA (1980) considered E. horni to be conspecific with E. sauteri , BOLTON (1995) treated them as different species with the former being a junior synonym of E. javanus (referred to as Pachycondyla javana ). In the material from Taiwan and Japan (except for Tsushima) examined by us the body size is more similar to that of E. horni , though rather variable, and the anteroventral corner of the pronotum is roundly angulate as in E. horni . These specimens agreed well with the original description and the images of the syntype of E. horni on ANTWEB (2024). We have thus concluded that the material we examined belonged to E. horni . TERAYAMA (2020: 90) tentatively treated the Japanese population as Ectomomyrmex sp. B , but inferred that it is most probably E. horni , reaching a conclusion similar to our view. At present it is not certain if E. sauteri and E. horni are conspecific or not as the available material of this species complex is still insufficient.

Apart from the status of Ectomomyrmex sauteri and E. denticepes , E. horni is clearly separated from E. javanus by the following combination of worker characteristics: 1) body small with head width 1.56–1.73 mm (2.03–2.23 mm in E. javanus ), 2) dorsum of head very densely and finely rugulose or punctorugulose; rugulae more or less regular, but frequently branching or reticulate (rugulae sharply defined and coarser, more constantly regular in E. javanus ), 3) lateral face of head weakly punctate-rugulose, matte (more coarsely rugulose in E. javanus ); 4) frontal lobe laterally with distinct smooth area (smooth area lacking or much less distinct in E. javanus ), 5) mandible generally with scattered punctures in basal half and well defined longitudinal striae in apical half, but essentially shiny (mandible opaque even if entirely without visible sculpture; striation, if any, microscopic in E. javanus ); 6) eye with sparse but conspicuous erect hairs (essentially without erect hairs in E. javanus ), 7) outer face of mid- and hindtibiae without erect hairs (with many erect hairs in E. javanus ). Two worker specimens from the Ogasawara Islands have slightly longer antennal scapes (1.54, 1.59 mm) and larger scape indices (SI: 86, 93) compared with workers from the Kyushu mainland and the Ryukyu Islands. More time is needed to entirely resolve the complicated problem surrounding E. horni and E. sauteri .

The Tsushima population of the E. javanus -complex (= E. japonicus (Emery, 1902) and E. sp. A of TERAYAMA et al. 2014) is more similar to the Korean and some other continental populations in having mandibles that are entirely striate and matte. The workers of these populations are constantly larger than those of E. horni , and the dorsum of the head has more regular rugae. Larger forms from Southeast Asia generally lack erect hairs on the eye, while in other characters they have various combinations of character conditions. DNA information is prerequisite for correct sorting of samples of this complex (currently assigned to E. javanus or treated as different species) from entire Asia into species.

Ectomomyrmex horni inhabits sparse forests and forest edges in Japan. Workers are often found under stones but nests are constructed in soil with complicated systems of passages and chambers.