Nudibranchs are a group of shell-less snail-like marine organism that are found in all of the Earth's oceans. Many, like the horned aeolid nudibranch (Hermissenda crassicornis ) seen in this week's photo, are brightly colored, which may be a means of advertising to potential predators that they are distasteful or poisonous. This is known as aposematic coloration. Other nudibranchs camouflage themselves to blend into their surroundings.
Some nudibranchs that specialize in feeding on animals that possess stinging cells have the unique ability to consume these stinging cells without triggering them, and then moving them into the feathery gills on their backs. This process gives them protection from predators, and while a naive predator may consume one such nudibranch, it is unlikely to dine on others after the painful surprise, thus providing protection for the other members of the species it might encounter.
The horned aeolid nudibranch is found along the Pacific coast of North America from Kodiak Island in Alaska, to Punta Eugenia half way down the Baja California Peninsula.
This photo was take with a Canon 10D dSLR with an EF 100mm lens. The shutter speed was 1/60 sec. at f/13 and ISO 200. The camera and lens were in an Ikelite underwater housing and light was provided by twin Ikelite DS-125 digital strobes in eTTL mode.