Common in the Solitary Islands Marine Park. Worldwide distribution in tropical and warm temperate waters, including the Mediterranean Sea. In Australia recorded from the southern Western Australian coast, through South Australia and Tasmania, the east coast north to central Queensland and including Norfolk and Lord Howe Islands.
Frequents area of reef where food sponges are found. Depth range from intertidal to at least 274 m.
Large external shell, usually with encrusting growth, only partly covers the large circular body. The body, covered with pustules, does not elongate when the animal is crawling and the animal has a large wide radula for feeding on food source sponges. The gills and rhinophores are just visible in the top photograph, the rhinophores used to provide oxygen rich water over the gills and sense the chemical signature of food sources from the water column. Grows to at least 15 cm in length, specimen pictured around 6 cm long.
Gary Cobb, David Mullins, Nudibranchs Encyclopedia, 2nd Edition, 2015. Publishers Thomas Slone, Masalai Press and Tim Hochgrebe, Underwater Australasia. p.86.
Australian Museum, Sea Slug Forum. http://www.seaslugforum.net/factsheet/umbrumbr. Accessed 29/09/2018.