Aetius nocturnus Deeleman-Reinhold, 2001

Dankittipakul, Pakawin & Singtripop, Tippawan, 2013, First description of the male of the little-known ant mimicking spider genus Aetius O. Pickard-Cambridge (Araneae: Corinnidae), Revue suisse de Zoologie 120 (4), pp. 575-583 : 577-581

Aetius nocturnus Deeleman-Reinhold, 2001

Figs 1-4, 6-18

Aetius nocturnus Deeleman-Reinhold, 2001: 336 , figs 502-504; description of female.

HOLOTYPE: ♀ ( RMNH, examined); Malaysia, Borneo, East Sabah, Danum Valley , primary forest, night collection; 6.-16.V.1991; leg. C.L. Deeleman.

NEW MATERIAL: 13, 1♀ ( MHNG); Thailand, Chiang Mai Province, Mae Jaem District, Doi Inthanon National Park, Doi Inthanon , 1260 m, evergreen hill forest behind national park headquarters, near pond (18°32.657'N 98°31.482'E); 20.VIII.2006; leg. P. Dankittipakul.

DIAGNOSIS: A. nocturnus can be distinguished by the following combination of characters: A short, truncate, posterior tubercle on the carapace in both sexes; opisthosoma with a tuft of white hairs at its rear end; male opisthosoma laterally constricted, female opisthosoma oblong; male palp distinctly elongate distally, with deep basal notch in retrolateral margin of cymbium; elongated, cylindrical embolus longer than bulbous part, with spiniform apex; a triangular RTA present; epigynal region elevated, with copulatory orifices opening posteriorly; spermathecae obtuse, with short, diverging posterior projections and acuminate fertilisation ducts.

NEW MALE: Total length 7.64; prosoma 3.80 long, 2.22 wide; opisthosoma 3.84 long, 1.94 wide.

Prosoma (Figs 4, 6, 8): Prosoma subpentagonal, convex, with broad central plateau abruptly sloping towards margin, highest behind ocular region, widest at two thirds of prosomal length, anteriorly with slightly protruded margin, posteriorly with stalk-like tubercle projecting backwards and overhanging pedicel, its apex truncate. Carapace dark chestnut-brown, integument strongly rugous, covered with numerous hairs, each situated on a minute elevation, forming faint radiating striae; fovea forming a broad and shallow depression. Chelicerae vertical, with a group of distomesal hairs; two denticles on each fang groove, promargin with small basal denticles, retromargin with similar-sized denticles situated close to each other. Sternum scutiform, convex, surface marked with numerous punctures, devoid of hairs; lateral margin adorned with short, triangular, sclerotised extensions fitting to coxae; spaces between coxae provided with sclerotised strips extending dorsally into pleural membrane, connecting sternum and carapace; posterior margin of sternum protruding between coxae IV, with a very narrow, digitiform projection.

Eyes (Fig. 8): AER straight, occupying half length of anterior margin of carapace; PER strongly recurved, much wider than AER, with PLE situated near lateral margin of carapace. Eye sizes and interdistances: AME 0.10, ALE 0.05, PME 0.08, PLE 0.08, AME-AME 0.14, AME-ALE 0.06, ALE-ALE 0.38, PME-PME 0.16, PME- PLE 0.20, PLE-PLE 0.72.

Legs: Measurements: Leg I 8.32 (2.26, 3.00, 1.82, 1.24); II 8.56 (2.48, 2.96, 1.82, 1.30); III 8.20 (2.52, 2.92, 1.80, 0.96); IV 10.92 (3.04, 3.86, 2.60, 1.42). Femora I, III and IV subdistally with one dorsal and one prolateral spine; femur II subdistally with one dorsal spine; anterior tibiae with three pairs of long ventral spines; posterior tibiae with two pairs of long and slender ventral spines; anterior metatarsi with two pairs of long ventral spines; posterior metatarsi with one pair of long and slender ventral spines; tarsi with claw tuft; scopulae indistinct.

Opisthosoma (Figs 4, 6, 7): Opisthosoma elongate-ovoid, laterally constricted, gradually widened posteriorly. Dorsal scutum heavily sclerotised, covering entire dorsal surface; epigastric scutum well-developed, extending anteriorly, forming short, grooved collar ring; ventral scutum rectangular, heavily sclerotised, situated between epigastric furrow and additional sclerotised posterior ring around the spinnerets.

Palp (Figs 12-17): Palpal femur not modified, slightly longer than palpal patella + tibia, with two curved spines at distal end. Palpal patella with one distal spine. Palpal tibia short, with distinct ventral depression; retrolateral tibial apophysis digitiform, weakly sclerotised, represented by transparent lamina; prolaterally with elevated ridge (PR). Cymbium distally elongate, lacking conspicuous spines, baso-retrolaterally strongly excavated, represented by semicircular notch (Fig. 15). Tegulum pyriform; part of subtegulum visible apico-retrolaterally of tegulum (Fig. 12), its prolateral protrusion indistinct (Figs 13, 17); sperm duct strongly convoluted, forming several posterior loops; embolus cylindrical, elongate, forming distal extension of the tegulum, abruptly tapering distally, apex bluntly pointed, almost reaching apex of cymbium.

FEMALE HOLOTYPE (Figs 3, 9): For body measurements see Deeleman- Reinhold (2001: 337). Carapace reddish brown, posterior tubercle dark brown. Opisthosoma dark reddish brown, with vague remnant of white pubescence. Dorsal scutum ovoid, almost reaching posterior extremity with a small tuft of white hairs. Ventral scutum rectangular, its anterior margin straight.

Genitalia (Fig. 9): Epigyne being part of epigastric scutum, epigynal region heavily sclerotised, represented by elevated, circular mound with two copulatory orifices situated on posterior lateral margin. Epigyne intact, not dissected, internal structure not examined.

NEW FEMALE (Figs 10-11, 18): General appearance as in male, including leg spination, but distinctly darker; anterior margin of carapace more or less straight, not protruded as in Fig. 8; opisthosoma more robust, posteriorly with tuft of white hairs; remnant of pubescence on dorsal scutum consisting of short hairs situated on wart-like elevations; ventral scutum rectangular, its anterior margin indented medially.

Genitalia (Figs 10-11, 18): Epigynal region distinctly elevated, with two semicircular copulatory orifices situated posteriorly. Spermathecae ovoid, touching one another, posteriorly with short, diverging tubes and acuminate fertilisation ducts.

VARIATION: Preserved specimens from Thailand apparently lost most of their hairs, except for a tuft of white hairs located at the posterior extremity on the female’s opisthosoma. This is also the case in the female holotype (Fig. 3). The coloration and pattern in the original description of A. nocturnus by Deeleman-Reinhold (2001) was presumably documented when the holotype was still alive. Photographs of a live spider from Singapore (Figs 1-2) show a similar pattern that conforms well to the original description. These photos were taken of a freshly moulted female.

NATURAL HISTORY: All specimens of A. nocturnus were collected in humid forests, suggesting that this species lives in pristine forests of SE Asia.

DISTRIBUTION: Borneo, Thailand (new record) and Singapore (new record).