It is usually grayish brown to dark gray in color with scattered black spots on the upper surface of the body.

These slugs inhabit environments with high humidity and shade, such as foothills and city gardens, although they are rarely seen.

It is the type species of the genus Rathouisia, which was named in honor of the Jesuit Père Charles Rathouis who made the original drawings of the specimens for Heude.

[1][2] The specific name leonina is from Latin word "leo", which means lion, referring to the predatory nature of the slug.

It is found in the following areas:[2] Rathouisia leonina has a cylindrical and elongated body, with a resting length of less than 35 mm (1 in).

[2] Rathouisia leonina often inhabits areas with high humidity and shade, but can also live in open habitats and in dry environments.