This flatworm achieves a size of 2-3cm. The bodyshape is oval and very flat. At the head they have two tentacles formed by the animals own body edge. The colour is pink with a central longitudinal white band and a dozen of fine white stripes. The body margin has also a white band.
Flatworms are carnivorous. All of them have predilection for sedentary and colonial animals like bryozoans, cnidarians, sea squirts, molluscs and some crustaceans or tube worms. Prostheceraeus roseus seems to feed on sea squirts of Genus Pycnoclavella .