
Philinopsis cyanea
Sihanoukville, Cambodia (2011).
Not a nudibranch but a headshield slug. Small as 1 cm or less.
Habitat:
Sandy bottoms. Coral reef
https://en.wikipedia.org/wiki/Philinopsis

Philinopsis cyanea is a species of sea slug in the family Aglajidae. It is black or brown with lighter patterns over its cylindrical body. They forage in sand and feed by enveloping their prey.
Similar species: Headshield Slugs
By Patomarazul
All rights reserved
Uploaded Aug 8, 2016. Captured Feb 24, 2011 08:55 in Kaoh Puos Rd, Krong Preah Sihanouk, Cambodia.