The study of an important collection of scorpions, belonging to the genus Chaerilus, recently collected from a cave in the Palawan Island, Philippines, allows the clarification of the identity of this population, often misidentified with Chaerilus chapmani Vachon & Lourenço, 1985 known from caves in the Gunong Mulu National Park in Sarawak (Borneo). Chaerilus agnellivanniorum sp. n. is described from the Puerto Princesa Underground River Cave in Palawan Island based on 14 specimens, males, females, and juveniles. The new species is totally distinct morphologically from Chaerilus chapmani, a true troglobitic species. Chaerilus agnellivanniorum sp. n. may also be a true troglobitic element, but with a less marked degree of regression for several characters. Some comments on the ecology of the new species and on regional biogeography of Borneo and Palawan islands are also proposed.
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