Myrmarachne amabilis Yamasaki, 2018

Yamasaki, Takeshi, Hashimoto, Yoshiaki, Endo, Tomoji, Hyodo, Fujio, Itioka, Takao & Meleng, Paulus, 2018, New species of the ant-mimicking genus Myrmarachne MacLeay, 1839 (Araneae: Salticidae) from Sarawak, Borneo, Zootaxa 4521 (3), pp. 335-356 : 338-339

Myrmarachne amabilis Yamasaki sp. nov.

( Figs 2–15 )

Type material. Holotype: male ( FRCS; LMy20140329_ KS), Sungai Liku , Lambir Hills National Park, Sarawak, Borneo, 29.III.2014, K. Shimizu leg. Paratypes: 1 male ( MNHAH; LMy20140328_ TY13 ), same locality as in the holotype, 28.III.2014, T. Yamasaki leg. ; 2 females ( MNHAH; LMy20140329_ TY19 ; MNHAH;

LMy20140329_TY20), same locality as in the holotype, 29.III.2014, T. Yamasaki leg.

Etymology. The specific name is a Latin adjective, meaning lovable and charming, referring to the small body size.

Diagnosis. Very small species, body length less than 3.0 mm; males distinguishable from other Myrmarachne species by apically swollen cheliceral paturon and flattened embolus; females distinguishable from other Myrmarachne species by narrow sclerotized copulatory ducts with twists near epigastric furrow. Myrmarachne amabilis sp. nov. is very similar to M. pumilio ( Karsch, 1880), but distinguishable by the shape of thoracic part: in lateral view, top of thoracic part is much lower than ALE in males and females of M. amabilis sp. nov., but just below ALE in males of M. pumilio, and higher than ALE in females of M. pumilio ( Benjamin 2015).

Description. Male ( Figs 2–6 ). Cephalic part remarkably higher than thoracic part. Cheliceral paturon almost twice longer than carapace, with seven prolateral and six or seven very small retrolateral teeth on fang furrow; anterior part swollen dorsally and laterally, posterior part narrower than anterior part and weakly swollen dorsally. Fang almost straight, without tooth-like apophysis on venter. Pedicel short. Abdomen oval, without constriction, mostly covered dorsally with scutum.

Male palp ( Figs 7–9 ). Cymbium oval, with one apical macroseta. Embolus thick and flattened; embolus coils oval, wider than cymbium. Spermophore running along posterior margin of tegulum. RTA well developed.

Leg macrosetae. Patella I pv 0, rv 1; tibia I pv 5, rv 5; metatarsus I pv 2, rv 2; tibia II pv 2–3, rv 2–3; metatarsus II pv 2, rv 2; legs III and IV with no macrosetae.

Coloration and setation ( Figs 3–5 ). Cephalic part black, covered with setae. Thoracic part pale brown to yellowish brown, almost without setae. Chelicera and fang pale brown; outer surface of chelicera sparsely covered with black setae. Labium dark brown. Endite brown. Sternum anteriorly dark brown, posteriorly brownish yellow. Abdomen cream, tinged with black. Coloration in living condition shown in Figure 2 .

Female ( Figs 10–13 ). Cephalic part higher than thoracic part; width of cephalic and thoracic parts almost same. Pedicel short. Abdomen oval, without constriction.

Epigyne ( Figs 14–15 ). Margin of copulatory atrium unclear. Sclerotized copulatory duct beginning just in front of epigastric furrow, extending to spermatheca with twists near epigastric furrow. Spermatheca ellipsoid; much wider than long. Slender median coupling pocket present between copulatory ducts in front of epigastric furrow.

Leg macrosetae. Patella I pv 0, rv 1; tibia I pv 5, rv 5; metatarsus I pv2, rv 2; patella II pv 0, rv 0–1; tibia II pv 3, rv 3; metatarsus II pv 2, rv 2; legs III and IV with no macrosetae.

Coloration and setation ( Figs 11–13 ). Carapace dark to light brown, with black cephalic part; cephalic dorsum covered with short setae and sparse long setae. Chelicera brown. Endite and labium brownish cream, tinged with black. Sternum tinged with black. Legs cream, with black lines on lateral surfaces. Abdomen covered with fine setae; anterior 1/3 cream, with one pair of small lateral spots fringed with white setae on dorsum; posterior 2/3 black. Live female appearance shown in Figure 10 .

Measurements (2 males / 2 females). Total length 2.5–2.6/2.8–2.9. Carapace length 1.18–1.28/1.30–1.35, width 1.00–1.06/0.85–0.86. Length of cheliceral paturon of male 1.97–2.10. Width of eye row I 0.99–1.01/0.88; II 0.88–0.89/0.78; III 1.06 –1.13/0.91–0.95. ALE–PLE 0.70–0.73/0.62–0.63; ALE–PME 0.35–0.38/0.32. Eye size: AME 0.34–0.36/0.29–0.31; ALE 0.18/0.15–0.16; PME 0.05–0.06/0.05; PLE 0.19–0.20/0.16. Abdomen 1.23–1.27/ 1.38–1.43.

Distribution. Known only from Borneo.

Remarks. Specimens were collected from shrubs along a trail across a secondary forest. The species often occurs with a particular ant species, Crematogaster inflata Smith. Myrmarachne amabilis is relatively similar to C. inflata in appearance, and the pale coloration of the thoracic part and anterior part of the abdomen enhances the similarity to C. inflata in the field. Ito et al. (2004) reported a species of the ant genus Camponotus Mayr mimics Crematogaster inflata , and the mimicry is effective to avoid predation by domestic chickens. Under attack by hostile ants and predators, Crematogaster inflata releases a white secretion from their metapleural glands ( Hölldobler & Wilson 1990; Yek & Mueller 2011). The secretion contains a mixture of phenolic compounds that are noxious to predators, and repel ant predators by acting both as a chemical deterrent and as a glue ( Attygalle et al. 1989; Jones et al. 2005; Maschwitz 1974). Therefore, this ant species might be a suitable model in Batesian mimicry for M. amabilis sp. nov.. Stable isotope analysis on ant-mimicking spiders reveals that M. amabilis relies on plant-based diets (Hyodo et al. in press: analyzed as Myrmarachne sp. H).

Figures

FIGURES 2–9. Myrmarachne amabilis sp. nov., holotype male (LMy20140329_KS). 2 in living condition, dorsal view; 3 dorsal view; 4 ventral view; 5 lateral view; 6 left cheliceral paturon and fang, ventral view; 7 left palp, ventral view; 8 retrolateral view; 9 left palpal tibia, dorsal view. Scales: 3–5: 1 mm; 6: 0.5 mm; 7–9: 0.25 mm.

FIGURES 10–15. Myrmarachne amabilis sp. nov., female paratype (LMy20140329_TY20). 10 in living condition, dorsal view; 11 dorsal view; 12 ventral view; 13 lateral view; 14 epigyne, cleared, ventral view; 15 dorsal view. Scales: 11–13: 1 mm; 14–15: 0.1 mm.