The Brown Trapania (Trapania brunnea) is a small nudibranch species that is known to occur in the waters of South-eastern Australia and northern New Zealand. In Australia it has been recorded in New South Wales, Victoria, Tasmania, South Australia and Lord Howe Island. This species is generally found living on sponges where it known to feed on small stalked animals called kamptozoa that can be found living on sponges. The body is coloured dark brown and it has irregular white blotches and spots on the body. This species looks very similar to Trapania benni however it lacks the paler reddish brown background colour with a covering of yellow or white specks.
The Brown Trapania (Trapania brunnea) grows to a maximum length of approximately 1.5cm.