Sason sundaicum, Schwendinger, 2003

Schwendinger, Peter J., 2003, Two New Species Of The Arboreal Trapdoor Spider Genus Sason (Araneae: Barychelidae) From Southeast Asia, Raffles Bulletin of Zoology 51 (2), pp. 197-207 : 198-202

Sason sundaicum , new species

( Figs. 6-32 )

Material examined. – Holotype – male (MHNG), Tone Sai Waterfall , Khao Phra Thaeo Non-hunting Area (7 59’N, 98 22’E), 50 m, Thalang District, Ko [= Island] Phuket, Thailand, coll. P. J. Schwendinger, 22-27 Sep.1997.

Paratypes – 1 male, 6 females, same data as for the holotype ; 1 male (matured early Oct.1997), 2 females (MHNG), from the type locality, 22 Oct.1996; 2 females (MHNG), Ko Siray, east coast (7 53’06.8'’N, 98 26’13.6'’E), 30 m, off Ko Phuket, Thailand, 11 Dec.2001 and 26 Jul.2002 ; 2 males, 1 female (MHNG), Ko Siray, Laem [=Cape] Nga (7 54’42.2'’N, 98 26’06.7'’E), 20m, 20./ 23.V.2003; 3 males (matured 16 Apr.1966, 23 Apr. 1996, 1 Mar.1997, respectively) (MHNG, ZRC), 3 females (MHNG, ZRC), forest behind Ao [= Bay] Molae (6 35’N, 99 40’E), 30 m, Ko Tarutao , Satun Province, Thailand, 12 Jan.1996 ; 3 females (MHNG, ZRC), forest outside Gua [= Cave] Landak, near Pantai [= Beach] Beringin (6 18’14.5'’N, 99 51’28.8'’E), 60 m, Pulau [=Island] Langkawi, Kedah, Malaysia, 29 Nov.2001 . All specimens coll. P. J. Schwendinger.

Others – 3 juveniles (MHNG), Ko Phuket ; 5 juveniles (MHNG), Ko Tarutao; 1 subadult male (MHNG), Pulau Langkawi. All specimens coll. P. J. Schwendinger.

Diagnosis. – Similar to S. andamanicum , distinguished by: body distinctly smaller; median labial cuspules of males short (only lateral ones filiform); prolateral megaspine on shorter spur more strongly inclined from axis of tibia I; embolus straight (not sigmoid), narrower at base, gradually tapering towards the tip ( Figs. 13, 14 ); scopula on metatarsus III indistinct or absent.

Description. – Male (holotype). Coloration generally light brown, slightly more reddish on pars cephalica of carapace, on dorsal chelicerae and labium. Area anterior to eye group subdivided into posterior, fully pigmented zone with fringe of hairs separating it from anterior hyaline zone ( Fig. 7 ). Ocular area very dark. Carapace with pairs of darkened bands (widening towards the periphery) radiating from fovea towards ocular area and (less distinctly) towards leg coxae. Distal part of chelicerae dark. Legs with dark lateral patches on distal portion of patellae (lighter on anterior legs); dark distal ring on tibiae broken by two light paramedian longitudinal stripes (leaving isolated dark median longitudinal stripe); entire dark ring present on metatarsi (shorter on anterior legs) (see Figs. 21, 22 , female). Palp with darkened lateral patches distally on patella and tibia. Opisthosoma light grey-yellow, with conspicuous dark pattern dorsally and ventrally ( Figs. 6, 10 ).

Carapace ( Fig. 6 ) hirsute, with dark bristles and fine light hairs on pars cephalica and on coxal elevations of pars thoracica; long bristles along lateral carapace margins. Ocular tubercle low; eye group rectangular, arranged in three rows; ALE in front of others; AME largest ( Fig. 7 ). Fovea very deep, slightly recurved.

Chelicerae weak, cheliceral groove with six teeth on promargin, long reddish bristles on retromargin and five/six tiny denticles basally between them. Rastellar area with one thick seta on each side.

Maxillae ( Figs. 8, 9 ) with two moderately elongated cuspules on prolateral-proximal corner.

Labium ( Figs. 8, 9 ) with transverse distal row of 11 cuspules; the median ones fairly short (with slightly bulbous base and peg-like apex); the lateral ones long, filiform and tapering to a point, similar to nearby setae but darker, basally wider, and more distinctly standing up from surface of labium.

Sternum ( Fig. 9 ) separated from labium by shallow groove (narrowest in the middle); only posterior two pairs of small, oval, submarginal sigilla discernible.

Palpus ( Figs. 13, 14 ) with cymbium carrying thin distal scopula dorsodistally and filiform, spatulate and clavate trichobothria dorsoproximally. Bulbus ovoid, with fairly straight and slender embolus evenly narrowing towards tip. Legs 3124. Paired tarsal claws without teeth. Thin ventral scopula distinct on tarsi I and II, and in distal portion of metatarsi I and II, indistinct on tarsus III, in distal portion of metatarsus III, and in distal portion of tarsus IV. Filiform trichobothria in two parallel rows dorsally on tibiae and metatarsi; three/four clavate and spatulate trichobothria in proximal half of tarsi, and triangular field (widening distally) of filiform trichobothria in distal half. All femora with longitudinal row of about five long, curved spines (or stiff bristles) dorsally. Low prolateral coupling spur on tibia I carrying slender, blunt, slightly curved megaspine pointing away from tibia at almost right angles; spur distinctly remote from distal margin of tibia I; prolateral-distal edge of tibia I deeply invaginated (retreated), i.e. fairly large area distal to (and on both sides of) tibial spur glabrous and unpigmented; four strong spines (the distal one fairly short and blunt, the proximal ones long and tapering) aligned in retroventral, longitudinal row on tibia I ( Figs. 11, 12 ). Four retroventral spines and one proventral-distal spine (not raised on spur and situated more distally) present also on tibia II, but less pronounced than on tibia I. Patellae I and II with one or two (in transverse row) retrolateral-distal spines.

Spinnerets ( Fig. 10 ): PMS short, digitiform; PLS threesegmented, apical segment short, with distal cluster of spigots.

Female (from the type locality). As male, but with relatively smaller AME ( Figs. 16, 17 ); carapace with distinctly fewer hairs; hyaline zone in front of eye group with median pigmentation; chelicerae stronger ( Fig. 16 ), with seven teeth on promargin of cheliceral groove and with single spinule plus one/two thick setae in rastellar area on each side; maxillae and labium carrying shorter and stouter cuspules of uniform size ( Fig. 18 ); legs 1=324, shorter, with much denser scopula on anterior legs (but also indistinct on tarsus IV); palpal claw with three denticles; palpal tarsus without claw tufts; pattern of dark markings on body and limbs more pronounced ( Figs. 16, 20-22 ). Spination of palp: four spines proventrally in distal portion of femur, two proventrally and one retroventrally on patella, three proventrally and three retroventrally on tibia. Spination of legs I and II: two spines (in transverse row) retroventral-distally on patellae, one proventrally and four retroventrally on tibiae. All legs with longitudinal row of up to nine spines dorsally on femora.

Vulva containing two widely separated spermathecae with rounded tips ( Fig. 23).

Measurements. – Male holotype, female paratype in parentheses. Body length 6.3 (7.7); carapace 3.1 (3.7) long, 2.8 (3.2) wide; maxillae 1.0 (1.2) long, 0.6 (0.7) wide; labium 0.3 (0.4) long, 0.6 (0.7) wide; sternum 1.7 (1.9) long, 1.5 (1.6) wide; opisthosoma 2.9 (3.7) long, 2.1 (3.0) wide; PMS 0.2 (0.2) long, PLS 1.0 (0.8) long. Eye sizes and interdistances: AME 0.32 (0.24), ALE 0.19 (0.19), PME 0.12 (0.09), PLE 0.13 (0.13); AME-AME 1.12 (0.19), ALE-ALE 0.61 (0.67), PME-PME 0.52 (0.61); eye group length 0.59 (0.60), front width 0.87 (0.93), back width 0.90 (1.00); MOQ length 0.41 (0.36), front width 0.70 (0.65), back width 0.69 (0.77).

Variation. – Males (n=8), females (n=15) in parentheses. Body length 5.7-6.8 (7.7-11.0), carapace length 2.8-3.2 (3.2- 5.0), width 2.7-3.0 (3.8-4.6). Zero to three (two to seven) cuspules are present on the maxillae, eight to eleven (seven to ten) on the labium; one female (from Ko Phuket) possesses a deformed labium carrying about 30 cuspules ( Fig. 19 ).

In the male holotype the retroventral-proximal spines on tibia I are slightly weaker and longer than in other males; in another male from Ko Phuket the distal spine in this row is tapering (blunt in all other males). A male from Ko Siray possesses an additional spine close to the retroventral-distal spine of its left tibia I. The scopula in the distal portion of metatarsus III is indistinct in some males from Ko Phuket and Ko Siray, indiscernible in the others. In a male from Ko Siray one of the median cuspules is filiform, otherwise no noteworthy variation in the shape of labial cuspules in males can be seen.

Females from Ko Phuket and Ko Siray have spermathecae which are entire ( Fig. 23) or subdivided into two or three terminal buds ( Figs. 24-27). All females from Ko Tarutao and Pulau Langkawi have the tips of their spermathecae divided into two or several buds ( Figs. 28-32), giving some of them a cauliflower-like appearance. Additionally, these latter females (from the southern localities) lack the spinule in the rastellar area, and the scopula on tarsus IV is indiscernible. The number of denticles on the palpal claws of females varies between two to six.

Etymology. - The species name refers to the Sundaland, i.e. the lands of the Sunda continental shelf, west of Wallace’s line.

Distribution. - The new species is known from four islands, i.e. Ko Phuket, Ko Siray, Ko Tarutao and Pulau Langkawi, off the west coast of the Malay Peninsula.

Biology. - Sason sundaicum , new species, occurs on trees in secondary forests and in tropical semi-evergreen rainforest (terminology according to Whitmore, 1991), or on isolated trees close to such forests. Most spiders were found near the sea: on Ko Tarutao and Pulau Langkawi only a few dozen or a few hundred metres from the coast; on Ko Siray even on trees washed by the high tide. On Ko Phuket, these spiders were collected along streams (never more than ca. 100 metres from the water), inside and at the edge of a forest situated about five kilometres from the sea.

The spiders occupy short silken nests which are equipped with two opposing trapdoors and usually fit into a depression so that the upper side of the nest is level with the surrounding surface ( Fig. 15 ; see also Pocock, 1900: 173; Raven, 1986: 50, 59, fig. 19). Most nests were found attached to the bark of living trees, where, due to interwoven bark particles and moss and/or lichens growing on them, they are perfectly camouflaged and very difficult to see (even for the experienced eye). The spiders appear to prefer trees with a fairly smooth bark which has depressions in it, but I have never found such nests on trees (like fig trees) with a completely smooth bark. On Ko Siray, S. sundaicum , new species, was found to be quite abundant on stems of coconut trees. On Pulau Langkawi some nests were seen both on vertical and overhanging sides of large boulders. Nests of males were 1.6-1.9 cm long, front door 1.0- 1.2 cm, hind door 0.9-1.2 cm wide; those of females were up to 2.8 cm long, front door up to 2.0 cm, hind door up to 1.8 cm wide. Silken nests on the bark of trees, very similar to those of Sason spp., are built by Poecilomigas abrahami (O. P.-Cambridge) ( Migidae ) from South Africa (see Griswold, 1987: 480-481, figs. 16-17). An undescribed Poecilomigas species from the Soutpansberg in the Northern Province of South Africa additionally builds its nest onto rock faces (personal observations; see also Filmer 1997: 119).

Mature males are present in different periods of the year: on Ko Phuket in September and October (two were collected mature in late September, one matured in early October), on Ko Tarutao in March and April (maturation in captivity) and on Ko Siray in late May (collected mature).

Females from Ko Phuket moulted twice per year, in April/ May and again in October; a female from Ko Siray in mid- December; females from Ko Tarutao in January, April, June and October; a female from Pulau Langkawi in mid-April (observations in captivity).

In late September 1997 four females with egg sacs and one with newly hatched spiderlings were collected on Ko Phuket. Egg sacs were lenticular, about 8 mm long and 6 mm wide, attached along their narrow side (for ca. 3 mm) to the ceiling of the maternal nest ( Fig. 15 ). One egg sac contained 40 first instar juveniles (white, immobile) with the cast egg membranes between their legs; in another egg sac 21 first instar juveniles and an unfertilised egg (1.4 mm in diameter) were found. The remaining two egg sacs were devoured by the females during transport from the forest. In late May 2003 two females were seen with well-developed (at least third instar), very active juveniles (in one case 18 spiderlings counted) in their nests on Ko Siray.

The presence of mature males at different times of the year suggests two mating periods [as also observed for the diplurid spider Phyxioschema suthepium Raven & Schwendinger in northern Thailand (Raven & Schwendinger, 1989: 59)]: 1) March to May and 2) September to October. Spiderlings observed in late May presumably resulted from matings in the first period, egg sacs and spiderlings collected in late September from those in the second period. It remains possible, however, that there is no limited reproductive period and that mating and egg laying actually take place all the year round.

Figures

Figs. 6-15. Sason sundaicum, new species. 6-14, male holotype. 6, body (without legs and palps), dorsal view; 7, eye group, dorsal view; 8, labium and proximal portion of maxillae, ventral view; 9, maxillae, labium and sternum, ventral view; 10, opisthosoma, ventral view; 11, left tibia I, prolateral view; 12, the same, ventral view; 13, distal part of palpus, ventral view; 14, the same, retrolateral view; 15, nest of female with egg sac suspended inside. Scale lines (6+10; 7; 8; 9; 11+12; 13+14) = 1.0 mm.

Figs. 16-22. Sason sundaicum, new species, two female paratypes. 16, body (without legs and palps), dorsal view; 17, eye group, dorsal view; 18, labium and proximal portion of maxillae, ventral view; 19, the same, different specimen; 20, opisthosoma, ventral view; 21, distal part of left leg I, dorsal view; 22, distal part of left leg IV, dorsal view. Scale lines (16+20; 17; 18+19; 21+22) = 1.0 mm.