Opalescent Sea Slug (Hermissenda crassicornis)
… occurs along the Pacific coast from Alaska to Mexico. Up to 3 inches (7.5 cm) long, they’re often found in tidepools and shallow areas of bays and estuaries. The brilliant colors are a warning to predators - the orange projections contain specialized cells that will sting.
Sea slugs are types of saltwater snails that lack shells. Like most land snails, they are hermaphrodites, with both male and female reproductive organs. However, they rarely self-fertilize; instead, they gather in mating groups to share sperm with other individuals.
photograph by Ken-ichi Ueda (Ken-ichi) on Flickr(via: Peterson Field Guides)