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Wednesday, April 23, 2008
By ROWAN HOOPER
Japanese name: Kamenote
Scientific name: Pollicipes mitella
Description: Also known as curl-footed barnacles, these animals are crustaceans, distantly related to crabs and lobsters, but goose barnacles attach themselves by a stalk to rocks. The tough, flexible stalk is known as a penduncle, and it can grow to around 8-cm long in adults. Attached to the stalk is the main body, which is covered by protective plates that increase in number with age. Like crabs, barnacles have legs, but barnacles don't use them to walk — they use them to waft the water toward them, hence the legs are modified into feeding organs. In fact, barnacles are the only kind of crustaceans that stay stuck in one place. Stalked barnacles are considered more "primitive" than the more familiar non-stalked forms.
Where to find them: Barnacles are exclusively marine, and tend to live in shallow and tidal waters, but will also be found on the hulls of ships and boats. Look for them in the tidal zone on rocky beaches from Hokkaido to Kyushu.
Food: Plankton and detritus — dead bits of plants and animals floating in the sea. The modified legs beat rhythmically to ensnare food particles and bring them to the central mouth. This type of barnacle is itself eaten by humans. Other enemies include limpets and mussels, which will displace them in the competition for a suitable place to live.
Special features: Barnacles go through two larval stages, first when they live freely, swimming in the water for the only time in their lives. The next larval stage is the settling stage, where they look for somewhere to attach to; somewhere they'll spend the rest of their lives. A place found, the larva cements itself to the rock (or boat) and starts to grow the tough plates that will protect it in adulthood. Barnacles are hermaphrodites, and as they are not able to move they stretch the penis out of the body, where it roams around searching for a mate. In proportion to body size, barnacles have the longest penis length of any animal (some seven times longer than the body). Barnacles, incidentally, play an important but overlooked role in the history of science: Charles Darwin made a detailed study of them in the years before he published "On the Origin of Species" in 1859.
PHOTO COURTESY OF BIO-IMAGE NET