Stegodyphus Simon

Miller, Jeremy A., Griswold, Charles E., Scharff, Nikolaj, Řezac, Milan, Szűts, Tamas & Marhabaie, Mohammad, 2012, The velvet spiders: an atlas of the Eresidae (Arachnida, Araneae), ZooKeys 195, pp. 1-144 : 79-83

Stegodyphus Simon

Stegodyphus Simon 1873: 336; 1892: 253; Lehtinen 1967: 265. Type species Eresus lineatus Latreille, 1817.

Magunia Lehtinen, 1967: 246. Synonymy in Kraus and Kraus 1988.

Note.

With the transfer of Stegodyphus annulipes to the genus Loureedia gen. n., the genus Stegodyphus contains 20 recognized species from Africa, southern Europe and Asia, plus a single species from Brazil ( Platnick 2011). The genus Magunia Lehtinen 1967 was established to accommodate Stegodyphus tentoriicola Purcell, 1904 and Stegodyphus dumicola Pocock, 1898, both of which have a bifurcated conductor including a hook-shaped sclerotized branch ( Kraus and Kraus 1988: figs 245, 248). Kraus and Kraus (1988) rejected this genus on the grounds that it would require dividing Stegodyphus sensu lato into at least three genera, which they considered needless. Molecular analyses have corroborated the monophyly of Stegodyphus sensu lato and nested taxa representing Magunia within (not sister to) a monophyletic Stegodyphus ( Johannesen et al. 2007; Miller et al. 2010a). We therefore concur with Kraus and Kraus (1988) in treating Magunia as a subjective junior synonym of Stegodyphus .

We studied specimens representing three Stegodyphus selected to cover a wide range of the variation present in the genus. Our exemplars were Stegodyphus lineatus , the type species for the genus, based on specimens from Afghanistan, Israel, and Turkey, Stegodyphus mimosarum based on specimens from Madagascar and Malawi, and Stegodyphus sarasinorum based on specimens from Myanmar. Our identification was based on the revision of Kraus and Kraus (1988); we did not seek to examine type material.

Diagnosis.

Distinguished from other eresids except Paradonea presleyi sp. n. by the median eye group, which has large, subequal eyes (AME/PME> 0.6) with clear separation on the horizontal axis and significant overlap on the vertical axis (Fig. 11A, C, E, G, I, K); distinguished from Paradonea presleyi sp. n. by the long, acute clypeal hood (short, slightly obtuse in Paradonea presleyi sp. n., Fig. 70I). Classically diagnosed by having the PER noticeably more narrow (65-90%) than the AER ( Kraus and Kraus 1988; Simon 1892); however, Adonea , and some Eresus and Paradonea species approach or even overlap with some Stegodyphus species. Further distinguished from other eresids except Dresserus , Gandanameno , and some Paradonea by the advanced position of the PLE (<0.29;> 0.31 in other eresids).

Distinguishing species.

Therevisionary monograph by Kraus and Kraus (1988) remains the key resource for identifying Stegodyphus species. Kraus and Kraus (1988) divided Stegodyphus into three species groups, each with one non-territorial permanently social species. In a molecular phylogenetic study, Johannesen et al. (2007) suggested that Stegodyphus lineatus is distinctive enough to warrant its own monotypic species group, but otherwise their findings were congruent with the earlier morphological study of Kraus and Kraus (1988) and supported the hypothesis that sociality in Stegodyphus has been independently derived multiple times. The Stegodyphus africanus group contains seven species including our exemplar, the social species Stegodyphus mimosarum . Males of the Stegodyphus africanus group have the palpal conductor as a distally-projecting complex comprising an outer leaf and a longer, less sclerotized, inner leaf. The embolic division is longer than the tegular division. The epigynum has the posterior part of median lobe raised, membranous, and wider than long. The median eyes in both sexes are relatively heterogenous (AME/PME ca. 0.6-0.8; data from Kraus and Kraus 1988). The Stegodyphus dufouri group contains four or five species (depending on whether Stegodyphus pacificus and Stegodyphus dufouri are considered distinct) including our exemplar, the social species Stegodyphus sarasinorum . Males of the Stegodyphus dufouri group have a spiral conductor that lacks a free inner leaf and is shorter than the tegular division. The median eyes in both sexes are relatively homogenous (AME/PME usually ca. 0.7-1.0, rarely ca. 0.6; data from Kraus and Kraus 1988). The Stegodyphus mirandus group contains six species including our exemplar, Stegodyphus lineatus , the type species of the genus (but see Johannesen et al. 2007). Males of the Stegodyphus mirandus group have complex conductors with a membranous inner lobe similar to that found in the Stegodyphus africanus group, although it is characteristically more spiral (as opposed to distally-projecting) and the embolic division is shorter than the tegular division. In some species ( Stegodyphus tentoriicola and Stegodyphus dumicola ), a sclerotized hook-like apophysis arises from the inner lobe of the conductor. The median eyes in both sexes are relatively homogenous (AME/PME ca. 0.8-0.9) except in Stegodyphus tibialis (AME/PME ca. 0.5-0.6; data from Kraus and Kraus 1988). The epigynum of some Stegodyphus mirandus group species is more or less rotated into vertical position ( Kraus and Kraus 1988).

Natural history.

Stegodyphus are known from a variety of warm, dry habitats and include both solitary and social species. The solitary species make webs with a central, funnel-like retreat and an irregular cribellate mass appressed to the substrate or multiple cribellate sheets in different planes on which they walk. The social species make a large nest of silk, plant debris and chitinous remains of their insect prey, and large sheets of cribellate silk may extend out in several directions (Fig. 4 J–L). The spiders walk upon or hang beneath these sheets. The cribellate silk carding leg is braced with a mobile leg IV, and the margins of the cribellate band are entire ( Griswold et al. 2005). We have never observed them to wrap captured prey. The fine structure of the cribellate silk of Stegodyphus was studied by Kullmann (1975) who recorded both axial fibers and reserve warp and noted that the cribellar fibrils are cylindrical in cross section. Prey include a variety of arthropods ( Dewar and Koopowitz 1970); social spiders hunting cooperatively are more effective than solitary hunters ( Ward and Enders 1985). Juveniles feed on the bodies of dead females (Fig. 3D), which may or may not be their mother in social species ( Schneider 2002). The sex ratio is female biased (more than 4:1) in social species ( Avilés 1997). Social colonies last for 7-8 years. Mating in many species occurs in December–February ( Kraus and Kraus 1988).