Nudibranch. These clams are like brightly colored little slugs and often serve as an object for photographing. Their bright coloration is a signal to enemies that they are inedible. For your own protection they use and other means. Some species have special glands that release a repellent, while others, eating with their shooting Hydrozoen cells, these cells accumulate in their tissues themselves become biting. Some shellfish, eating sponges, cover his body calcium and silicon spicules of the latter, thus erecting these shells.