Bright colors and nudibranchs go together like ham and eggs, thunder and lighting, or peanut butter and jelly. With their ability to absorb nasty chemicals or stinging cells from their prey and store them, most have evolved the bright warning coloration found in noxious species, or their mimics, throughout the animal kingdom.
What’s the use of a defense system if no one else knows you have it? So this advertising alerts potential predators to avoid prey that looks like this. Having once gotten a mouthful of foul taste or nasty stings, a fish is likely to remember not to try that again. And while that particular nudibranch may not survive the encounter, others of the species will be protected by it.
Commonly known as MacFarland’s chromodorid, or the three-stripe doris, this brilliantly colored species is typically found from Monterey, California, USA south to Bahia Magdalena, Baja California Sur, Mexico, and are typically most abundant along the southern California coast, but even there they aren't common. The twin rhinophores on the head are sensory organs, and the branchial plume at the opposite end, which can be withdrawn into the body for protection, provide for the exchange of oxygen and carbon dioxide between the water and the animal’s bloodstream.
This photo was taken at Santa Catalina Island, part of the Channel Island chain, off the coast of California using a Canon EF100 mm f/4 macro lens on a Canon EOS 10D in an Ikelite underwater housing. Lighting was provided by two Ikelite DS-125 Substrobes in eTTL mode. The exposure was set to 1/60 sec at f/22 and ISO 100.