Nudibranchs
Nudibranchs are a widespread and successful group of marine Gastropod molluscs. The name means 'naked gills'. They are shelless and uncoiled Gastropods, famous for their brilliant colours. There are more than 3000 known species. Nudibranchs are one of the groups which are informally known as sea slugs. This is a term which includes other Gastropod groups which look similar to nudibranchs. Sea slugs is an informal term; it is not a monophyletic group.
Colors and defense
Flabellina pedata, a nudibranch from East Timor Among this group can be found the most colorful creatures on earth. In the course of evolution, sea slugs have lost their shell, and have developed other defense mechanisms. Their anatomy may resemble the texture and color of the surrounding plants, giving them camouflage (crypsis). Many have an intense and bright coloring, which warns that they are distasteful or poisonous (warning colouration). Nudibranchs that feed on hydroids can store the hydroids' nematocysts (stinging cells) in the dorsal body wall.[4] The nematocysts wander through the alimentary canal without harming the nudibranch. Then, the cells are brought to specific places on the creature's hind body. Nudibranches can protect themselves from the hydroids and their nematocysts. It is not yet clear how, but special cells with large vacuoles probably play an important role. They can also take in plants' chloroplasts (plant cell organelles used for photosynthesis) and use them to make food for themselves. Another method of protection is the release of a sour liquid from the skin. Once the specimen is physically irritated or touched by another creature, it will release the slime automatically.
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