Myotis vivesi is the largest species in the genus Myotis in the Americas, and is similar in size to the Eurasian Myotis myotis (greater mouse-eared bat).
The skull averages 23 millimetres (0.91 in) in length.
The second largest Myotis species in the New World, Myotis velifer, has a skull 17.6 mm (0.69 in) long, and feet 8 mm (0.31 in) long; M. vivesi has greatly elongated hind feet, which average 23 mm (0.91 in) long.

In common with other fish-eating bats, Myotis vivesi has long, efficient wings, with high aspect ratio and low wing loading, and large feet with sharp claws.
The uropatagium (the wing surface between the hind legs) bears a fringe of silky hairs of unknown function; the uropatagium itself is used in hunting.

The fur is around 8 mm (0.31 in) long, and varies in colour from fawn to brown, with the base of each hair being dark grey.
In common with other piscivorous species of Myotis, the underside of M. vivesi is pale.
Myotis vivesi is the largest species in the genus Myotis in the Americas, and is similar in size to the Eurasian Myotis myotis (greater mouse-eared bat). The skull averages 23 millimetres (0.91 in) in length. The second largest Myotis species in the New World, Myotis velifer, has a skull 17.6 mm (0.69 in) long, and feet 8 mm (0.31 in) long; M. vivesi has greatly elongated hind feet, which average 23 mm (0.91 in) long.
In common with other fish-eating bats, Myotis vivesi has long, efficient wings, with high aspect ratio and low wing loading, and large feet with sharp claws. The uropatagium (the wing surface between the hind legs) bears a fringe of silky hairs of unknown function; the uropatagium itself is used in hunting.
The fur is around 8 mm (0.31 in) long, and varies in colour from fawn to brown, with the base of each hair being dark grey. In common with other piscivorous species of Myotis, the underside of M. vivesi is pale.
Myotis vivesi