Spiders are successful predators that inhabit nearly all kinds of terrestrial and even freshwater habitats. However, only a handful of representatives colonize the marine intertidal zone. The intertidal trapdoor spider genus Idioctis is one of the unique spiders that build their nests below the marine hightide line. The genus also features its highly disjunct distribution on the isolated Indo-Pacific land masses.
In this study, we describe a new intertidal trapdoor spider species, Idioctis parilarilao sp. nov., from southern Taiwan and Green Island (Lutao), which are around 3,000 km away from the nearest know distribution in Singapore. Both morphological comparisons and phylogenetic analyses support that I. parilarilao from two separate localities from Taiwan are conspecific, and distinct from its morphologically closest species, I. xmas, from Christmas Island, Indian Ocean.
Given the lack of representation of other species in public databases, our COI gene tree should be seen as preliminary, but it does support the monophyly of the genus Idioctis. As the genus was not previously known from East Asia, our discovery vastly extends the distribution range of Idioctis and the family Barychelidae. Given the tectonic and volcanic specifics of the history of Taiwan and Green Island, and the direction of the known oceanic currents, we provide a preliminary explanation of the biogeographic and diversification history of intertidal spiders in the region that may involve rafting.
