Ceratosoma tenue (Abraham, 1876)
Uncommon in the Solitary Islands Marine Park. Widespread throughout tropical western Pacific and Indian Oceans. In Australia recorded from Queensland south to northern New South Wales, Lord Howe and Norfolk Islands. Also North West Shelf off Western Australia.
Found on reef edges to a depth of 30 m. Feeds on sponges.
May be coloured red to brown, there is a distinctive tall appendage behind the gills. This "defensive horn" is a defensive lure and contains most of the distasteful chemicals stored from its food. There is a large anterior lobe on either side of the head and a large lobe on each side of the gills. Between these there is a smaller lobe which is joined by a ridge to the gill lobe but not the head lobe. The edge of the lobe and the ridge joining the posterior lobes is outlined with a broken purple line. There is usually no purple line between the middle lobe and the head lobe. Grows to 120 mm.
Australian Museum, Sea Slug Forum. http://www.seaslugforum.net/find/ceratenu. Accessed 19/07/18.
Gary Cobb, David Mullins, Nudibranchs Encyclopedia, 2nd Edition, 2015. Publishers Thomas Slone, Masalai Press and Tim Hochgrebe, Underwater Australasia. p.114.