Nudibranch Hypselodoris kanga
"This is Hypselodoris kanga. It can be distinguished from similarly coloured species such as H. infucata by the shape and colour of the gills. If you look carefully, the gills of H. kanga are triangular in cross-section and there are white or yellow spots on the smooth outer edge of each gill. This animal is feeding on the dark blue sponge. The extended oral tube of the animal is clearly visible. The sponge is almost certainly a species of Dysidea".
Australian Museum, Sydney
Locality: Lembeh Strait, Indonesia, Indo pacific, 28 April 2006, muck dive. Length: about 70 mm.