Hypselodoris saintvincentius from Sth Australia

Dear Carl,
It certainly in general shape looks like Ceratosoma amoena and they are both in the family Chromodorididae, but this is Hypselodoris saintvincentius, a species restricted to south and south-western Australia.

Concerning books on South Australian sea slugs. Have a look at the Book Review Section. The book by Fred Wells & Clay Bryce - Sea Slugs of Western Australia, and Neville Coleman's 1001 Nudibranchs - Catalogue of Indo-Pacific Sea Slugs cover some of the fauna you will encounter, but we still have quite a bit to learn about the fauna of that part of Australia. You have a mixture of local endemic species found nowhere else, another group found across all of temperate Australia, and a third group of tropical species which sometimes appear to hitch a ride as larvae, in warm water currents down the west Australian coast.
Best wishes,
Bill Rudman