Bifurcitus ducalis, formerly Megadytes ducalis, is a species of water beetle in the family Dytiscidae. It is the largest species in the family. Until recently, the species was only known from a single specimen that was collected in the 19th century from Brazil, but more specimens, also collected in the 19th century from Brazil, were discovered in 2019. Although listed as extinct by the IUCN, the limited studies conducted on water beetles in Brazil means that it might still survive.

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