Tylodina corticalis (Tate, 1889)
small umbrella shell
Tylodina corticalis

sub-classs Opisthobranchia > order Umbraculida > family Tylodinidae

Tylodina corticalis is bright yellow with large head, a limpet-like shell, and and exposed gills on the right side of the body. For this reason, Tylodina corticalis is sometimes referred to as a side-gilled slug. It feeds on sponges and lays yellow egg coils.

Distribution =  [] only from southern Qld south to southern WA
Max size =  rarely to 12cms, usually less than 50mm

more info at Sea Slug Forum     more pics at nudipixel