Gasteracantha mengei Keyserling, 1864

Tan, Ji, Chan, Zi Yang, Ong, Ching Ang & Yong, Hoi Sen, 2019, Phylogenetic relationships of Actinacantha Simon, Gasteracantha Sundevall, Macracantha Hasselt and Thelacantha Simon spiny orbweavers (Araneae: Araneidae) in Peninsular Malaysia, Raffles Bulletin of Zoology 67, pp. 32-55 : 46-47

Gasteracantha mengei Keyserling, 1864

( Figs. 1I , 9 A−F, 10A, B)

Gasteracantha mengei Keyserling, 1864: 67 , pl. 1, fig. 5 Gasteracantha malayensis van Hasselt, 1882: 13

Gasteracantha mengei Dahl, 1914: 270 , fig. 10

Material examined. Holotype – female, Malacca, Peninsular Malaysia, “ Det. N. Scharff Ex. Dry Collection ”, no date, BMNH.

Others: 1 female (damaged abdomen) (reg. UIR270615- GMEN1 ), Sungai Sedim, Kedah, coll. Tan J and Chan ZY, 27 June.2015 .

Diagnosis. Female individuals of G. mengei can be differentiated from female G. diardi and G. diadesmia Thorell (see Fig. 4 , p. 33 in Roy et al., 2017 and Fig. 615 in Sen et al., 2015) by the somewhat parallel arrangement of its anterior and median spines in dorsal view as well as the inconspicuous posterior spines ( Figs. 1I , 9A , 10A ). In terms of epigynal structure, the protruding Y-shaped structure of the epigyne in posterior view ( Fig. 9D ) can be used to distinguish G. mengei from G. diardi .

Natural history. One female individual was collected from a large web (~ 1 m) built across two trees near a river in a disturbed forest.

Distribution. Thailand, Malaysia, Singapore and Borneo.

Remarks. G. mengei can be confused with G. diardi as the females are similar in terms of size, appearance and geographical distribution. Despite the failure to obtain any DNA data for G. mengei GMEN 1, a cross-check with the holotype specimen ( Fig. 10 ) clearly showed that these two species are different. It is worth noting that the four tiny posterior sigilla (arrow in Fig. 10 ) observed in the G. mengei holotype (then ‘ G. mengii ’, labelled ‘Det. N. Scharff Ex. Dry Collection’ from Malacca, Peninsular Malaysia) were not illustrated or described in Keyserling (1864). This may have led to the incorrect synonymy of two morphologically similar species, namely G. mengei and G. malayensis ( Simon, 1864) as the subsequent authors, i.e., Dahl (1914) and van Hasselt (1882) often relied on illustrations for identification. Both Gasteracantha species were also coincidentally from the same type locality of Malacca. These two species are unique within the genus as they both lack conspicuous posterior abdominal spines. However, they can be distinguished based on the presence of the row of four posterior sigilla as well as the angle and position of the median and posterior spines. According to Simon (1864), the two pairs of spines of G. malayensis are ‘straight and parallel’ (p. 285 and Fig. 130 in Simon, 1864), unlike the abdominal spines of G. mengei which are slightly angled towards the posterior ( Figs. 9A , 10A ). These morphological characters also distinguish the females of these two species from those of G. quadrispinosa O. Pickard-Cambridge, 1879 from Australia and New Guinea, a species thought to be conspecific with the former two due to the lack of information on abdominal colors at that time ( Pickard-Cambridge, 1879; Dahl, 1914; Chrysanthus, 1971; World Spider Catalog, 2018). Photographic records suggest that both G. malayensis and G. mengei are extant in Peninsular Malaysia and more sampling is required for validation, considering the possibility of ethanol preservation affecting not only the color but also the natural direction of the spines as pointed out by Pickard-Cambridge (1879).

Figures

Fig. 1. General habitus. A, Actinacantha globulata (Walckenaer, 1841), sub-female; B, Gasteracantha diardi (Lucas, 1835), female; C, G. diardi yellow morph, female; D, G. diardi white morph, sub-female; E, G. kuhli, female; F, Gasteracantha hasselti C. L. Koch, 1837, female; G, Macracantha arcuata (Fabricius, 1793), female; H, Thelacantha brevispina (Doleschall, 1857), female; I, G. mengei Keyserling, 1864, female. Photos by Tan Ji.

Fig. 9. Gasteracantha mengei Keyserling, 1864. A, Dorsal habitus; B−E, Epigynal structure. A, Ventral view; B, Posterior view; C, Lateral view; D, Dorsal view; E, Anterior view. Scale A = 5 mm; B−E = 100 µm. S = Spermatheca.

Fig. 4. Bayesian tree based on the CO1 dataset of Actinacantha, Gasteracantha, Macracantha and Thelacantha. Numeric values at nodes arranged in an order of Ultrafast ML bootstrap support/MP bootstrap support/Bayesian posterior probability.

Fig. 10. Holotype sample of Gasteracantha mengei Keyserling, 1864 deposited in the Natural History Museum, London. A, Dorsal view of abdomen; B, Posteroventral view of epigyne. Scale not available. (Photo reproduced with permission from Joseph Koh).