Spiders are one of the most diverse groups of terrestrial Arthropods, but are only rarely found in aquatic environments. Species that live in freshwater environments include the Fishing or Raft Spiders, Dolomedes spp., and the Eurasian Water Spider, Argyroneta aquatica. Spiders able to inhabit marine environments are even rarer, with examples including several members of the Family Dictynidae, Several genera of Jumping Spiders, Salticidae, a single genus each of Anyphaenid Spiders and Desid Spiders, Amaurobioides and Cambridgea, respctively, as well as some populations of the Swollen Jaw Spider, Oedignatha scrobiculata.
Among Mygalomorph Spiders, only a single genus is known to ever enter marine environments, the Intertidal Trapdoor Spiders, Idioctis spp., which construct burrows beneath the marine high tide line. These burrows are lined with a silk which apparently provides a reliable barrier against salt water, preventing the sea from entering the burrow when the tide is high. Members of this genus are known from island environments scattered across the Indian and Pacific oceans, apparently indicating an ability to occasionally disperse across wide areas of open ocean, although individual species tend to be restricted to single islands, or sometimes very close groups of islands, suggesting that such dispersals are rare.
In a paper published in the Journal of Arachnology on 6 October 2023, Kuang-Ping Yu of the Evolutionary Zoology Laboratory at the Slovenian National Institute of Biology, and the Department of Biology at the University of Ljubljana, Ying-Yuan Lo at the Department of Life Science at the National Taiwan Normal University, and the Zoology Division at the Taiwan Endemic Species Research Institute, Ren-Chung Cheng of the Department of Life Sciences and Research Center for Global Change Biology at the National Chung Hsing University, Robert Raven of the Biodiversity and Geosciences Program at Queensland Museum, and Matjaž Kuntner, also of the Evolutionary Zoology Laboratory at the Slovenian National Institute of Biology, and of the Jovan Hadži Institute of Biology, the Department of Entomology at the Smithsonian National Museum of Natural History, and the State Key Laboratory of Biocatalysis and Enzyme Engineering and Centre for Behavioural Ecology and Evolution at Hubei University, describe a new species of Indertidal Trapdoor Spider from Taiwan.
The new species is named Idioctis parilarilao, where 'parilarilao' refers to both the name of the southernmost tip of Taiwan in the Paiwan language of the island, as well as to the indigenous people of the area. Specimens were discovered living both in Pingtung County on the southern tip of the Taiwanese mainland, and on Green Island, which lies off the east coast of that mainland. Female specimens ranged from 9.1 mm to 12.7 mm in length, the males were not observed. All specimens were light brown in colour, with a covering of thin, greyish hairs.
Idioctis parilarilao was observed inhabiting tubular burrows dug into Coral rocks or cliffs within the intertidal zone, emerging at night when the tide was low to ambush small Arthropods. The trapdoors were covered by a camouflage incorporating Coral sand, debris, and Algae. The burrows were connected to natural chambers within the rock, which served as reserves of air at low tide. Breeding behaviour of the species is unclear, but large numbers of spiderlings were seen on rocks above the tideline in October.
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