These common littoral animals are actually highly modified crustaceans,
not molluscs or shells.
In fact, the main ingredient of the popular fried oyster dish, "Oh
Luak" or "Oh Chien" has sometimes been incorrectly attributed to barnacles
instead of oysters.
Barnacles also attach
themselves to other animals like crabs.
mature free-swimming larvae, which resemble mussel
shrimps, attach onto rocks head first, glueing themselves by means
of a strong protein cement, and forming calcareous plates around themselves.
During high tide their modified legs protrude to catch planktonic
They are important as fouling organisms, their presence often serious
enough to considerably slow ships down. Scraping them off is an expensive
and laborious task. Recently, barnacles have become important in dentistry
since their strong protein cement has been found to be useful in fitting
The flat and small Chthamalus, the star barnacle (Family Chthalmalidae),
occupies the highest tide levels while the volcano barnacle, Tetraclita
(Family Balanidae) is the largest, its lateral valves being indistinct.
They are more common in open areas, in the upper parts of the littoral
zone. The less common stalked goose barnacles (Family Lepidae) are
sometimes seen on driftwood or flotsam.
Some barnacles have become tiny parasites.