Abstract
This paper provides descriptions of two new theridiosomatid species, Theridiosomanigrivirgatum sp. nov. and Sennintanikawai gen. nov., sp. nov. from the Ryukyu Islands, southwest Japan, with photographs and illustrations of both sexes. Sennin gen. nov. is a troglophilic genus composed of two species, S.tanikawai sp. nov. (Iriomote Island, Japan) and S.coddingtoni (Zhu, Zhang & Chen, 2001), comb. nov. (southern China). Zomadibaiyin Miller, Griswold & Yin, 2009, which recently joined the Japanese fauna, was morphologically reexamined based on specimens from the Ryukyus, and taxonomic features of Zoma males were reassessed. A distributional map of theridiosomatid spiders in the Ryukyus is also provided, including T.dissimulatum Suzuki, Serita & Hiramatsu, 2020, and T.alboannulatum Suzuki, Serita & Hiramatsu, 2020 with their habitat types, web morphology, and web-building behavior in detail.