Endless forms most wonderful: Four new cavernicolous planthopper species (Hemiptera, Fulgoromorpha, Cixiidae and Meenoplidae) from the Canary Islands

The Canary Islands harbour a rich and diverse fauna of obligate subterranean arthropods (i.e. troglobionts). Among the insect taxa which have repeatedly undergone the evolutionary switch from life on the surface to underground environments are the Fulgoromorpha, or planthoppers: Cixiidae and Meenoplidae. Previously, a total of 13 troglobitic planthopper species have been described from El Hierro, La Palma, Tenerife and Gran Canaria. Here we describe three new troglobitic cixiid species: Cixius palmirandus sp. nov. from La Palma, Cixius theseus sp. nov. from El Hierro and Tachycixius gomerobscurus sp. nov. from La Gomera, and one new meenoplid species: Meenoplus skotinophilus sp. nov. from El Hierro. Tachycixius gomerobscurus sp. nov. is the first record of a subterranean adapted Fulgoromorpha on La Gomera. With now 17 documented species of strictly hypogean planthoppers, the Canary Islands hold the highest number of subterranean planthoppers of any region worldwide, representing ca. ¼ of all known species. We provide a key to all subterranean planthopper species known from the Canary Islands as well as information on their habitat, distribution, ecological classification and conservation status. As all highly specialized, narrow range troglobitic planthopper species must be regarded as vulnerable, if not endangered, climate change poses a major risk of extinction. We hypothesize on island colonization and subterranean speciation underlying taxonomic diversity and high endemicity. We conclude that the currently observed zoogeographic patterns imply the existence of an ancient fauna which is now extinct.