Lagoa Misteriosa, a novel source of beetle diversity: two new species of Brazilian riffle beetles (Insecta: Coleoptera: Elmidae: Elminae) with immatures from a karst sinkhole

Elmidae comprises the largest aquatic family of Dryopoidea, with 1,650 species recorded worldwide. Brazil has the most diversity with 210 described species. Although this number has increased in recent years, in some Brazilian geographical regions there are knowledge gaps in the distribution of fauna, especially based on immature stages. After a yearlong aquatic insect survey conducted in a karst sinkhole located in Jardim municipality, Mato Grosso do Sul State, Brazil, we found an endemic and novel beetle fauna which included new species. Here we present a taxonomic description of two new species of Elmidae, Microcylloepus dimorphus sp. nov. and Hexacylloepus misteriosa sp. nov., based on males, females, and immatures. These new species represent the first Brazilian Elmidae described from a lentic habitat. Also, we provide photographic images of the habitus, SEM images, and illustrations of the diagnostic structures for both species, including their immatures, and habitat notes about Lagoa Misteriosa.