"Haloed Chromodoris" - undescribed species, formerly assigned to genus Chromodoris, and listed in Coleman.
Listed in Burn’s 2006 paper of Bass Strait / SE Australian nudibranchs.
https://museumsvictoria.com.au/media/6159/mv-science-reports-10.pdf
Various examples are here:
http://www.dancingfish.com/gallery/photos/Adelaide07/large-cr/070108_008.jpg
http://www.aboutken.com/kendiving/imgidnudi/nudi020.jpg
NB This species is not Ceratosoma brevicaudatum
Figure 4 of this report shows the two species together: https://www.adelaidescuba.com/Documents/Dive%20Resources/Neville%20Coleman%20Memorial%20Nudibranch%20Dive%20Report%202015%20and%202016%20(Baker%20et%20al.).pdf