Theridiidae, Sundevall, 1833

Breitling, Rainer, 2021, A completely resolved phylogenetic tree of British spiders (Arachnida: Araneae), Ecologica Montenegrina 46, pp. 1-51 : 28

Theridiidae

The phylogenetic framework for this family is based on the results of Liu et al. (2016), combining morphological and molecular evidence, with additional genera and species added according to the morphological analyses of Agnarsson (2004).

The genus Steatoda in the usual sense is clearly highly polyphyletic in the analyses by Liu et al. (2016); creating a monophyletic Steatoda s. lat. would require merging the genus with both Crustulina and Latrodectus (and possibly other Asagenini); certainly not a desirable solution. Instead, Steatoda is here tentatively divided into a number of smaller genera, all of which had been postulated previously, as classic authors have long recognised the heterogeneity of the genus. It is, however, important to realise that the molecular subdivisions are not closely aligned to previous morphology-based ideas (e.g., Wiehle 1937; Wunderlich 2008), and the two sets of results are difficult to reconcile.

Relationships within Enoplognatha are based on barcode data, E. oelandica being placed based on morphology (but with low confidence). The semispecies relationship between E. ovata and E. latimana is based on Lasut et al. (2015) who show convincing evidence based on mitochondrial and nuclear markers indicating that the two forms are not yet fully reproductively isolated, despite their obvious genitalic differences. Levi (1973) cites a personal communication from V. Seligy stating that both forms of the genitalia can be found among siblings from the same egg sac.

The internal topology of Robertus is also based on barcodes, but with weak support, the placement of R. insignis being based on its similarity to the barcode-sequenced R. lyrifer ( Almquist 1978) .

Phycosoma inornatum is here considered a member of Lasaeola, following Wunderlich (2020). This placement is problematic, given that both of the genera, as well as Dipoena , seem to be poorly delimited. The transfer to Lasaeola is justified by the observation that European “ Phycosoma ” is unlikely to be congeneric with the type species from New Zealand: it lacks an epigynal scapus [present in true Phycosoma ] and has a relatively large embolus and conductor [small in true Phycosoma ]; the male prosoma is also very different and matches that of other Lasaeola species. The species thus lacks the most important genus diagnostic characters of Phycosoma . Otherwise, the arrangement of the species is maximally conservative and maintains Dipoena and Lasaeola as separate genera, despite concerns about their possible para- or polyphyly. Arrangements within each genus are based on morphological similarities (e.g., Miller 1967).

Dipoena (Lasaeola) lugens is a phantom species in the sense of Breitling et al. (2015, 2016), probably not native and not reported again since the original description. It is thus considered a nomen dubium and not included in the tree.

The relationships between the three Episinus species are inferred from their barcode sequences.

The placement of Coleosoma floridanum is uncertain, as it is not necessarily congeneric with the species analysed by Liu et al. (2016). The placement of Simitidion as sister of Phylloneta is based on Wunderlich (2008; general morphological affinity) and Knoflach (1996; mating behaviour). The placement of Theonoe is based on Agnarsson et al. (2007).

Cryptachaea riparia is considered a member of Parasteatoda , based on the arguments detailed in Breitling (2019d). The internal relationships between the Parasteatoda species are based on barcode data and morphology.

The relationships between the Rugathodes species are based on morphological similarities.

The genus Theridion is clearly polyphyletic on a global scale, and its phylogeny inferred on the basis of morphology and barcode data is not always consistent with more comprehensive molecular phylogenies. To retain monophyletic genera in the tree, T. pinastri is placed in Allotheridion , following Archer (1950): barcode data place the species very close to the type species, and the general genus concept proposed by Archer seems validated by the molecular data, including the closeness to Phylloneta . The transfer of T. hannoniae to the same genus is based on its membership in the petraeum -group ( Bosmans et al. 1994). Platnickina tincta is returned to Theridion s. str., to be conservative and avoid changing the name of common species that have always been placed in Theridion .