Trapania brunnea was described from New South Wales, Australia. It has also been reported from Victoria, Tasmania and New Zealand.
This Brown Traoania is translucent pale brown with a meshwork pattern of darker brown covering most of the body apart from some irregular patches around the gills and rhinophores and along the midline of the back. The lateral papillae, gills and rhinophores are mostly translucent pale brown, with some brown markings.
Similar to Trapania benni.
This species feeds on Entoprocta which often grow on sponges and other living substrata.