The species classically grouped in the genus Zygiella F.O. Pickard-Cambridge 1902 are thought to all possess a characteristic orb web feature – a spiral-free sector in the upper part of the orb. Zygiella s.l. has recently been split into four genera, Zygiella s.s., Leviellus Wunderlich 2004, Parazygiella Wunderlich 2004 and Stroemiellus Wunderlich 2004, and proposed to belong to family Zygiellidae, rather than the classical Araneidae. To find orb web features that could potentially diagnose these species and/or genera, we investigated female web architectures of L. thorelli, P. montana, S. stroemi, Z. keyserlingi and Z. x-notata. We investigated a total of 278 female webs and compared 16 characters emphasizing web size, web and hub asymmetry, as well as radial and spiral counts. The free sector may be present in all species but its prevalence in female webs varied from 41% in Z. keyserlingi to 94% in P. montana. Various combinations of web architecture characters may diagnose those species that in our sample represented all four genera: Zygiella s.s. may be diagnosed by the median number of non-circulating sticky spirals below hub, Stroemiellus by the small web size with small mesh width and the non-circulating spirals above hub, Parazygiella by few primary radii and sticky spirals, and Leviellus by a pronounced vertical hub displacement. This suite of diagnostic features may provide preliminary support for the current taxonomy of Zygiella s.l., although the ultimate test, i.e., a phylogeny, is needed to test the validity of the genera. Seven out of 16 web characters are potentially phylogenetically informative because they show a statistically significant shared variation among species. Our study, which pioneers the quantification of web data to distinguish species, implies that the interspecific variation in webs may turn out to reflect phylogenetic relationships among Zygiella s.l.
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Vol. 38 • No. 2