This small nudibranch (Chromodoris lochi) was found crawling along the finger of a sponge on a dive trip to Tawali in PNG.
Nudibranchs are perhaps the most photographed creature in the sea, due to the fact that stay still for photographers, and that they can be very attractive subjects.
The key to a good nudibranch photo, I believe, is to find a perspective that is interesting, and also to get a background (negative space) that complements the subjects, and at least doesn’t distract from it.
This is one of my personal favourites as it is shot from front on (not tops down) and has a non-distracting background. The left to right orientation gives the appearance of motion.
Additionally the rhinopores are sharp, and the depth-of-field provides a good blur (bokeh) through the rest of the image.