Myrmarachne acromegalis, Yamasaki, Takeshi & Ahmad, Abdul Hamid, 2013

Yamasaki, Takeshi & Ahmad, Abdul Hamid, 2013, Taxonomic study of the genus Myrmarachne of Borneo (Araneae: Salticidae), Zootaxa 3710 (6), pp. 501-556 : 505-507

Myrmarachne acromegalis sp. nov.

( Figs 2 A–F, 3A–E, 41C–F)

Type material. Holotype male, Mamut, Ranau, Sabah, BORNEO, 22 III 2008, H. Takizawa leg. (UMS). Paratypes: BORNEO: 1 female (UMS), Danum Valley, Sabah, 10 IX 2005, Y. Hashimoto leg.; 1 male (UMS), same loc., 12 I 2008, Y. Hashimoto leg.; 1 female (UMS), Lahad Datu, Sabah, 19 X 2009, T. Yamasaki leg.; 1 male and 2 females (BMNH), Sukau, Sabah, 20–21 X 2009, T. Yamasaki leg.; 1 female (UMS), Muaya, Sabah, 27 X 2009, T. Yamasaki leg.; 2 males and 2 females (BMNH), Tabin Wildlife Reserve, Sabah, 15 X 2010, T. Yamasaki leg.; 1 male and 1 female (MSNG), Sukau, Sabah, 18 X 2010, T. Yamasaki leg.; 1 female (UMS), Maliau Basin, Sabah, 7–10 XI 2011, T. Yamasaki leg.

Non-type material examined. NE. THAILAND: 2 males, Haui Nam Keam, Wang Nam Kheao dist., Nakhon Ratchasima prov., 18 VIII 2009, T. Yamasaki leg.

Diagnosis. In males, chelicera apically swollen and basally narrow, with numerous prolateral and retrolateral teeth ( Fig. 2 C); fang without tooth-like apophysis. In females, cephalic part convex above PLE dorsally and thoracic part dorsally swollen ( Fig. 3 B); sclerotised copulatory ducts complexly twisted; median pocket present in front of epigastric furrow.

Measurements (male/female). Carapace length 2.25–(2.55)/2.40–2.70, width 1.24–(1.58)/1.20–1.34. Abdomen length 1.90–(2.45)/1.95–3.50. Chelicera length 2.20–2.90 (2.75). Sternum length 1.28–(1.55)/1.28–1.43. Width of eye row I 1.12–(1.26)/1.14–1.28; II 1.01–(1.18)/1.09–1.18; III 1.16–(1.34)/1.22–1.36. ALE–PLE 0.84– (0.98)/0.88–0.94; ALE–PME 0.39–(0.44)/0.39–0.45. Eye size: AME (0.38)–0.39/0.38–0.41, ALE 0.18–(0.21)/ 0.19–0.21, PME 0.05–(0.06)/0.05–0.06, PLE 0.19–(0.21)/0.19–0.20.

Male ( Figs 2 A–F, 41C, 41E). Cephalic part weakly convex or almost flat dorsally. Thoracic part in lateral view lower than lower margin of PLE, with dorsum almost flat anteriorly, and sloping downward posteriorly. Chelicera apically swollen and basally narrow, with eight prolateral and nine or ten retrolateral teeth; prolateral apical corner of venter of chelicera bearing tooth-like apophysis. Fang weakly sinuous without tooth-like apophysis. Sternum slender, slightly overlapped by coxae I and II. Abdomen oval, with dorsal scutum that is strongly incised on each lateral outline anteriorly.

Palp ( Figs 2 E–F). Tegulum oval with strongly curved seminal reservoir in anterior part of tegulum. Embolus forming two oval coils; embolus coils occupying almost half of venter of cymbium. RTA thick, curved inward. With palp in dorsal view anterior margin of tibia projecting near RTA ( Fig. 2 F). Flange of RTA not developed well. Leg spination. Femur I md 2–3, pd 1; tibia I pv 3–4, rv 4; metatarsus I pv 2, rv 2; femur II md 2, pd 1; tibia II pv 0– 1, rv 2–3; metatarsus II pv 2, rv 2; femur III md 1–2, pd 1, rd 0–1; tibia III pv 0–1; femur IV md 2, pd 1, rd 1.

Coloration and pilosity. Two distinct forms recognisable, the “golden hairy” and the “shiny” forms. “ Goldenhairy” form: Carapace dark brown to black, covered with dense hairs (in natural light with a golden shine). Chelicera anteriorly broadened and black, posteriorly narrower and dark brown, covered with fine hairs; white hairs present around boundary between broadened and narrow portions of chelicera. Maxilla, labium and sternum pale brown to brown tinged with black. Coxae I, III and IV tinged with black; coxa II cream white. Abdomen densely covered with fine hairs (in natural light, with golden reflection); abdomen dark brown to black, dorsal scutum dark brown. “ Shiny” form: Carapace dark brown to black, almost without hairs except for clypeus; thoracic part with shiny surface. Chelicera, maxilla, labium, sternum and coxae much as in “golden-hairy” form. Abdomen covered with fine hairs; dorsal scutum dark brown to black; remaining integument except for scutum greyish brown.

Female ( Figs 3 A–E, 41D, 41F). Cephalic part strongly convex dorsally. In lateral view dorsal concavity between cephalic and thoracic parts distinct. Thoracic part strongly convex dorsally; summit of the convexity lower than upper margin of PLE; in dorsal view lateral margin of thoracic part weakly convex above coxa III. Chelicera with six or seven prolateral and ten retrolateral teeth. Sternum slender, strongly overlapped by coxa II. Abdomen oval with weak constriction anteriorly; anterior part of dorsum weakly sclerotised.

Epigyne ( Figs 3 D–F). Copulatory atria containing openings oval. Sclerotised copulatory ducts thick, complexly twisted in anterior part, and proximally slightly swollen. Median pocket present in front of epigastric furrow.

Leg spination. Tibia I pv 4, rv 4; metatarsus I pv 2, rv 2; tibia II pv 1, rv 2; metatarsus II pv 2, rv 2; tibia III pv 0–1.

Coloration and pilosity. Two distinct forms (“golden-hairy” form and “shiny” form) recognisable, as in males.

Etymology. The specific name is derived from the shape of the male chelicera, which is apically swollen and basally narrow (Latin adjective: “ acromegalis ” (acromegalic)).

Distribution. Thailand, Borneo.

Remarks. Although the two forms look very different, we here regard these as belonging to the same species because other than coloration and pilosity, they share most morphological characters including the structures of the male palp and epigyne and because they are often found together at the same sites. We have observed some male/ female pairs of the “golden-hairy” form at nest sites, but male/female combination is not yet confirmed for the “shiny” form. The male and female of different forms have not been observed to coexist at the same nest sites, so the possibility remains that these two forms are different biological species as well (ie separated by behaviour, life cycle, mating activity).

Biology. The species is arboreal, and occurs in both human-managed environments like house gardens, and natural habitats like forest canopies. The “golden-hairy” form is in external appearance similar to Camponotus leonaldi Emery and the “shiny” form to Dolichoderus sulcaticeps Mayr. Previous instances that one species mimics several ant species have been reported (Cushing 1997; McIver & Stonedahl 1993; Nelson 2010). In Tawau Hills Park the shiny form was found near a satellite nest of D. sulcaticeps , but no interaction between the spiders and the ants was observed ( Fig. 41 B).

Figures

FIGURE 2. M. acromegalis sp. nov., male. A, body, dorsal view; B, chelicera and carapace, lateral view; C, chelicera and fang, ventral view; D, maxillae, labium, sternum and coxae; E, palp, ventral view; F, palp, dorsal view. (Scales. A – D: 1 mm; FIGURES E – F: 0.25 mm)

FIGURE 3. M. acromegalis sp. nov., female. A, body, dorsal view; B, chelicera and carapace, lateral view; C, maxillae, labium, sternum and coxae; D – E, internal structures of epigyne, ventral view; F, internal structure of epigyne, dorsal view. (Scales. A – C: 1 mm; D, F: 0.25 mm; E: 0.10 mm)

FIGURE 41. A, male and female of M. hanoii, with Dolichoderus sp. cf. taprobanae (ants) and its satellite nest, Borneo. B, Dolichoderus salcaticeps (ants) and its satellite nest, Borneo. C, shiny form of M. acromegalis sp. nov., male, Borneo. D, shiny form of M. acromegalis sp. nov., female, Borneo. E, golden fairly form of M. acromegalis sp. nov., male, Thailand. F, goldenfairly form of M. acromegalis sp. nov., female, Borneo. (Scales. C, F: 1 mm / division)