Megadytes ducalis

Megadytes ducalis is a species of water beetle in the family Dytiscidae. With a length of , it is the largest species in the family. Until recently, the species was only known from a single specimen that was collected in the 1800s from an unknown locality in Brazil, although rumors indicate it was found in the bottom of a canoe in the Amazon. In 2019, a study reported 10 additional specimens (including the first female of the species), all collected from the end of the 19th century, discovered incidentally in various historical collections. While the original holotype lacked any location data, the new specimens all indicate that they were collected in Santo Antonio da Barra (now known as Condeuba) in the southern part of Bahia, Brazil. Villagers in the region were involved in insect trade, capturing the much sought after specimens of "Hypocephalus armatus" found around the region. As a consequence of the lack of recent records, the IUCN lists it as extinct. Considering the absence of information about the species and the limited studies conducted on water beetles in Brazil, it might still survive.