Liphistius isan Schwendinger 1998
Creators: name: Schwendinger, Peter J.
Publisher: name: Zenodo
Year: 2013
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Arachnida
Araneae
Liphistiidae
Liphistius
Liphistius isan

description: Liphistius isan Schwendinger, 1998
Figures 2 A–B, F, 3A–F, I–P
Types. THAILAND: Sakon Nakhon Province, Kud Bak District, Phu Phan National Park (16°48’N, 103°54’E, coordinates corrected using Google Earth), 450–520 m; male holotype, 3 male and 2 female paratypes; leg. P.J. Schwendinger, 8.XII.1994, 7.XII.1995; all deposited in MHNG.
New material. THAILAND: Ubon Ratchathani Province, Khong Chiam District, near Sroi Sawan Waterfall (15°27’37”N, 105°34’43”E), 220 m; 1 male (matured 15.VIII.2012); leg. P.J. Schwendinger, 31.XII.2011 (sample TH-11/21), deposited in MHNG. LAOS: Champasak Province, Phou Asa, near Ban Kiatngong (14°45’38”N, 106°01’53”E), 270 m; 6 males (2 collected mature, one matured in early X.2010, others matured 22.IX.2011, 10.X.2011, 11.X.2011) and 4 females; leg. P.J. Schwendinger, 29.IX.2010 (sample LT-10/22); one male and one female deposited in SMF, all other specimens in MHNG.
Extended diagnosis. Liphistius isan is a medium-sized species with carapace, chelicerae and femora to tibiae of legs and palps orange in females (Fig. 2 B) and juvenile males. It differs from the similar and geographically close L. dangrek Schwendinger, 1996 by distinctly smaller body size [range in carapace length and width of males (n=11) 6.0–8.1 and 5.6–7.3, respectively (specimen from Sroi Sawan largest), in L. dangrek (n=10) 9.8–13.3 and 8.9–11.7, respectively; maximum carapace length and width of females (n=6) 8.6 and 7.5, respectively, in L. dangrek (n=13) 14.8 and 13.5, respectively]; males differ by pedipalps with a basally wider retrolateral tibial apophysis in ventral view (Fig. 3 A) (not looking knob-shaped as in L. dangrek, see Schwendinger 1996: fig. 33) and with a distinctly longer paraembolic plate (Fig. 3 B–F, cf. Fig. 3 G–H); females differ by a narrower posterior stalk of the poreplate (Fig. 3 M–P, cf. Schwendinger 1996: figs 37–38).
Variation. In alcohol, all males from Laos have a uniformly dark brown opisthosomal tergite I followed by mostly light yellowish brown tergites II–X with small dark spots at the spine bases and near the lateral margins (see Fig. 2 A for a live spider). The male types have all tergites dark brown, with small light spots along the posterior margin. The male from Sroi Sawan is intermediate, with a uniformly dark brown tergite I and extensive dark patches on tergites II–X, its tergite II being almost uniformly dark. The opisthosomal tergites in females from Laos are mottled with light spots, whereas in females from the type locality these are almost uniformly dark. The palp illustrated in the original description shows a fairly narrow paracymbium in ventral view (Schwendinger 1998: fig.
2C, Schwendinger 1999: fig. 2C) and a rounded paraembolic plate (Fig. 3 E, Schwendinger 1998: fig. 2D, Schwendinger 1999: fig. 2D). However, both characters are variable to a certain degree (Fig. 3 A, K and Fig. 3 B– F). The contrategular process is absent or indistinct (Fig. 3 I) in all males (in contrast to L. nesioticus and L. suwat), recognizable (very short and widely truncate instead of pointed or rounded) only in one male from Laos (Fig. 3 J). Most females have a poreplate with thick ventrolateral rims carrying more or less distinct anterior protuberances (lobes) (Fig. 3 M– O); in one female from Laos the lateral rims are not thicker than the anterior rim and they lack protuberances (Fig. 3 P).
Measurements of males (n = 11) range: body length 14.0– 19.8 mm, carapace length 6.0– 8.1 mm, carapace width 5.6–7.3 mm. The corresponding maximal measurements in females (n = 6) are: 24.5, 8.6, 7.5. Males from Laos are generally a little smaller than those from Thailand (carapace length 6.0–7.4 versus 6.0–8.1, width 5.6–6.5 versus 5.6–7.3; the male from Sroi Sawan is the largest) and have slightly longer and slightly stronger bristles on the cumulus (these being generally short and thin in members of this species assembly).
Relationships. Liphistius isan belongs to the Liphistius trang species group, and within that to species complex A, an assembly of morphologically similar species in the eastern part of Thailand which also includes L. dangrek, L. nesioticus Schwendinger, L. ornatus Ono & Schwendinger, L. phileion Schwendinger, L. sayam Schwendinger and L. suwat Schwendinger (see Schwendinger, 1998; there inappropriately called superspecies A). Liphistius dangrek appears to be closest to L. isan, but if variability in the size of the contrategular process and in the posterior stalk of the poreplate of L. suwat is actually larger than recognized at present, then the latter could be closer to or even synonyomous with L. isan.
Distribution and habitat. This species is known from three localities in northeastern Thailand and southern Laos, on both sides of the Mekong River (Fig. 1, localities 2a–c). All spiders were found in seasonally dry, deciduous forests in the lowlands. At the locality in Laos, burrows of small spiders were seen on old termite mounds in a dry and degraded (by human activity) part of the forest, whereas all adult spiders were found in a more humid part with larger trees and a closed canopy. This indicates that L. isan (as also the closely related L. dangrek) is relatively tolerant of seasonally dry conditions, which is reflected in its relatively wide geographical distribution.
Biology. At Phou Asa (in Laos) three adult males were collected at the end of September, one became mature a few days later, the other three males matured in captivity (in Geneva) in September and October of the following year. Males from Thailand became mature a little earlier in the year (types in July, male from Sroi Sawan in August), which could be due to captive rearing. A few newly abandoned burrows, of the same size as those in which the adult males were found, were also seen at Phou Asa, indicating that some males had then already left their burrows to search for females. The larger spiders (mature males and females) reacted to disturbance by “tiptoeing” (repeatedly raising the body high on all eight legs) and spreading their chelicerae.
One female from Laos constructed an egg case in captivity at the beginning of December 2010. It was 2.3 cm in diameter and 1.8 cm high, and contained 71 cream-coloured eggs suspended above the bottom of the egg case in a hammock of very fine threads.
All burrows were unbranched and closed by a single trapdoor with its hinge on the upper side or laterally. In penultimate males the doors were 2.0– 2.8 cm wide and 1.5–2.0 cm long; in females up to 3.5 cm wide and up to 2.4 cm long. Up to eight signal lines were spread over the soil surface only (not over rocks or roots). The longest burrow was 24 cm long.
None of the spiders of this species examined were carrying ectoparasitic mites.
description: Published as part of Schwendinger, Peter J., 2013, On two Liphistius species (Araneae: Liphistiidae) from Laos, pp. 51-60 in Zootaxa 3702 (1) on pages 53-56, DOI: 10.11646/zootaxa.3702.1.2, http://zenodo.org/record/284544