Brachionus nilsoni is a euryhaline (tolerates a wide range of salinity) rotifer in the family Brachionidae.

The anterior dorsal margin has six thin, acutely pointed spines.

Its mental edge is firm and elevated, with a small median notch.

Its foot aperture is small and sub-square dorsally, while being large and U-shaped ventrally.

Found in small numbers in Mud and Ottawa Creeks in northwest Ohio.