Bornella hermanni have an elongate body.This body shape is typical of the genus Bornella.The rhinophores are stalked, the lateral processes paired on the dorsum.The background colour is a translucent cream with a broken network of red-orange lines on the dorsum. The body sides are scattered with opaque white granules or sometimes irregular patches. The colour pattern can extend onto the rhinophore stalk and the dorsal processes.
Very similar is Bornella stellifer. In Bornella hermanni there are three pairs of dorso-lateral processes, in Bornella stellifer there are five or six pairs.
Seaslugs genus Bornella feeds on hydrozoon polyps.