Under the water
Elyria clarkia sea slug (not a nudibranch, but a sacoglossa) - photo from Pierce et al, via The Sea Slug Forum; found in the Florida Keys; up to 1.75" long and 1.15" wide; This sea slug eats algae and "retains living chloroplasts which continue to photosynthesize within its body, providing it with some sugar.
Color + Design Blog / Nudibranchs, The Most Colorful Creatures in the World by COLOURlovers
NUDIBRANCH?! "There are over 3,000 known species of nudibranchs, and scientist estimate that only half have been discovered so far. The creatures soft-body and short life span of 1 year make it possible for many of them to live undetected and vanish from the earth without a trace."