I shot this footage of a sacoglossan (sap-sucking slug) in May in the Lembeh Strait.
I was unable to find a match for it in my references, and Terry Gosliner (on the strength of 1 frame grab), reckoned it was a new species of Stiliger sp., so I made a little YouTube video of it.
I particularly like how you can see the material traveling up and down the ducts of the digestive gland.
Shot with my Panasonic GH4 in a Nauticam NA-GH4 housing. I used an Olympus M.Zuiko ED 60mm f2.8 macro lens and a Nauticam CMC. Quite a lot of the shots are cropped from 2160p to 1080p to give more effective magnification.