Nelio is a genus of marine bivalve molluscs of the family Malletiidae.
Shells of Nelio have a more strongly developed hinge, most prominently on the anterior hinge, when compared to members of the genus Malletia.
The genus was first described in 1854 by Arthur Adams.
Members of the genus have been found in the Pacific Ocean, Caribbean and the Southern Ocean. The earliest fossils of the genus date to the Cretaceous, and have been found in Antarctica and Argentina.
Species within the genus Neilo include: