Cuthona methana is a species of sea slug in the family Tergipedidae. It is small, only 4 to 6 millimeters in length, with long gills. C. methana was discovered on a seafloor at Hydrate Ridge, with layers of methane hydrate, which is a mixture of seawater and methane. It was named for being discovered near methane bubbling out of the seafloor, giving the species name "methana".