Barnacles

Barnacles are masters of living in the intertidal zone and have evolved some key adaptations that help them survive and dominate in such a hazardous environment. Barnacles are a family of marine crustaceans so they are closely related to crabs and lobsters.

More specifically they belong to a class of crustaceans called Maxillopoda and are of the infraclass Cirripedea. The name Cirripedea basically translates into “feather legs” and barnacles are called cirripods because they have heavily modified legs that look very much like feathers and they use them to catch food from in the water when the tide is in.

Adaptations and body structure

These little crustaceans are very well adapted to life in the intertidal zone. They have developed special glands which produce a cement like substance to help secure them to the rocky shore and other hard surfaces. A calcareous outer shell composed of five or more plates, helps to absorb the impact of waves which allows barnacles to thrive in areas where heavy wave exposure is common and an operculum, which is two moveable plates, can open and close so at high tide a barnacle can open to release their cirri (feather-like legs) to catch passing food and then close during low tide to reduce the amount of water lost while they are exposed to the Sun.

Types of barnacles

Two sub-orders of barnacles exist: the belanomorpha and lepadomorpha barnacles, which have one big distinction and are commonly known as the acorn and goose barnacles. The lepadomorph barnacles grow a stalk which is attached to the substrate whereas the plates of balanomorph barnacles attach directly to the substrate.

Life cycle

The life cycle of a barnacle is relatively simple; they reproduce sexually and a larval nauplius is released and drift with the zooplankton. When it’s ready it undergoes a transformation into its second and final larval form of the cypris/cyprid. The sole task for the cypris larvae is to find a hard substrate to settle on. As the cypris finds a suitable substrate, it cements itself down and spends the rest of its life in the one solitary location