Distribution: Uncommon in the Solitary Islands Marine Park. Distributed throughout the Indo-Pacific region, from Sth Africa and the Red Sea to Hawaii, north to Japan, south to Australia. In Australia recorded from around Shark Bay in Western Australia, across the north of the continent, the Great Barrier Reef in Queensland south to northern New South Wales.

Ecological Notes: Feeds on sponges, Family Halichondriidae. This specimen photographed at a depth of 12 m.

Additional Notes: A large nudibranch with blue to blue-grey background colour, recognised by the 3 to 6 longitudinal tuberculate dorsal ridges. A central ridge is always present, the rhinophores are yellow. Grows to 115 mm.

References: Gary Cobb, David Mullins, Nudibranchs Encyclopedia, 2nd Edition, 2015. Publishers Thomas Slone, Masalai Press and Tim Hochgrebe, Underwater Australasia.  pp.257-8.

Undersea Jewels, A colour guide to nudibranchs, Gary Cobb and Richard C Willan. Australian Biological Resources Study, Canberra, 2006. p.229.

Atlas of Living Australia website at https://bie.ala.org.au/search?q=phyllidia+varicosa+. Accessed 29/05/2019.