Balanus is a common and widespread genus of medium-to large barnacles, some growing to a size able 10 cm / 4 in across. Today they are found living on most rocky shorelines and they are extremely abundant worldwide. Balanus, like most other crustaceans, begins life as a tiny planktonic larva (young form). However, during this juvenile period, it loses most of its typical crustacean features, such as a long body with numerous walking limbs. The larva spends a month or more floating through the ocean, moulting several times before settling onto a firm base.