Fishcake - I made this cake for my daughter's birthday (she was in her at the time) - simple, great fun to decorate. The 'water' is a piece of board covered with holographic melinex gift-wrap, the gradation of colour just comes from the lighting.
Yes, this is an animal. The Spanish dancer (Hexabranchus sanguineus - meaning "blood-colored six-gills") is a dorid nudibranch (sea slug). I think it's great color and design inspiration for a crocheted afghan.