One of the best known examples of symbiosis is that between the hermit crab and a sea anemone (e.g. , Adamsia). The anemone is often found attached to the shell in which the hermit crab lives. In their long history hermit crabs have developed the habit of sheltering within the empty shells of mollusks such as periwinkles and whelks. The hind portion of the has lost its hard covering and would otherwise be unprotected. As the crab gets bigger it outgrows its shelter and so has to find a new one. Often, a sea anemone attaches itself to the crab’s shelter and it may envelop part of the crab’s own shell as well. The growth of the crab and anemone keep pace with each other and the crab has no need to change its shell – more and more of its is sheltered by the anemone. As the crab moves about in search of food the anemone is brought into contact with a greater supply of food and the crab is protected by the anemone’s stinging cells.