Three new species of Grouvellinus Champion, 1923 from Maliau Basin, Sabah, Borneo, discovered by citizen scientists during the first Taxon Expedition (Insecta, Coleoptera, Elmidae).

Further results are presented of the first field course at Maliau Basin, Malaysian Borneo organized by Taxon Expeditions, an organization which enables citizen scientists to be directly involved in taxonomic discoveries. Three new species of the aquatic beetle genus Grouvellinus Champion, 1923, namely G. leonardodicaprioisp. n., G. andrekuipersisp. n., and G. questsp. n. were collected jointly by the citizen scientists and taxonomists during the fieldwork in Maliau Basin. Material was mainly sampled from sandstone bottom rocks of blackwater streams at altitudes between 900 m and 1,000 m using fine-meshed hand-nets. The genus is widely distributed in the Oriental and Palearctic regions, but these are the first records from the island of Borneo.