Theridiosoma O. Pickard-Cambridge, 1879

Suzuki, Yuya, Hiramatsu, Takehisa & Tatsuta, Haruki, 2022, Two new species and a new genus of ray spiders (Araneae, Theridiosomatidae) from the Ryukyu Islands, southwest Japan, with notes on their natural history, ZooKeys 1109, pp. 67-101 : 67

Genus Theridiosoma O. Pickard-Cambridge, 1879

Type species.

Theridiosoma gemmosum (L. Koch, 1877), from Nuremberg, West Germany (not examined).

Remarks.

Males of Theridiosoma species can be distinguished from other theridiosomatid genera by the morphology of the embolic division of the male palp: short and tubular embolus with embolic apophyses fragmented into several long bristle-like parts ( Coddington 1986a: figs 131, 133). Embolic apophysis varies in number and shape among species and is regarded as an important taxonomic character (e.g., Zhao and Li 2012; Suzuki et al. 2020). Median apophysis is less sclerotized, curved and attenuates distally ( Coddington 1986a: figs 132, 133), which is less useful for distinguishing species. A sclerotized projection ('conductor projection’) is present on prolateral side of conductor in some species, while absent in others ( Coddington 1986a; Suzuki et al. 2020). Distal margin of conductor beneath embolic apophyses ('posterior margin of embolic division’ in Suzuki et al. 2020) is generally sclerotized and the shape is useful as a taxonomic character (e.g., Suzuki et al. 2020: figs 7E, 8E, 10E, 11E). Tegular surface beneath conductor is generally sclerotized with many folds (referred as 'ventral side of tegulum beneath posterior edge of embolic division’ in Suzuki et al. 2020), of which shape and surface texture vary among species ( Zhao and Li 2012; Suzuki et al. 2020).

Females of the genus can be distinguished from related genera ( Baalzebub , Epilineutes and Wendilgarda ) by having relatively sclerotized, robust copulatory ducts running from the bursa to the spermathecae ( Coddington 1986a: figs 145, 152). Surface of epigynal plate is smooth and its posterior margin generally lacks scape-like structures. Shape of posterior margin of epigynal plate varies among Theridiosoma species: rounded or almost straight in some species, while having a pair of small, sclerotized processes (named as ‘spurs’ in Coddington 1986a) or a small slit-like invagination in others ( Coddington 1986a; Miller et al. 2009; Suzuki et al. 2020). Zoma females possess a similar genitalia except in having a sclerotized median pit on the surface of the epigynal plate and lacking any processes nor invaginations on the posterior margin of the epigynal plate in known species ( Saaristo 1996; Miller et al. 2009; Zhao and Li 2012; Ballarin et al. 2021).