What is a Barnacle, Actually?
Barnacles are peculiar "Shellfish" Related to Shrimp, not Oysters
A Big Barnacle Begrudgingly Serving as an Anchor for Many Smaller Barnacles
Barnacles seem to be the ultimate shellfish, appearing to be a shelled mollusc akin to a mussel, oyster or clam. They are everywhere, they are incredibly adaptable and wherever they settle, hardy to the extreme.
But this is a false similarity that is entirely superficial. While barnacles do indeed have hard, calcium based shells, they start life as small, free swimming larvae that look similar to miniature lobsters before settling down and becoming sedentary filter feeders. Barnacles are not relatives of oysters, clams or mussels at all, but crustaceans just like crabs, lobsters, shrimp and isopods. There are many different types of barnacles, ranging from small, familiar types often seen on rocky shorelines to bizarre gooseneck barnacles that are sometimes eaten, due to the increased palatability of these larger organisms with distinctive fleshy necks. Then there are the giant barnacles that can measure 6 inches wide and 12 inches tall. These monsters are called Giant acorn barnacles and are denizens of the Northeast Pacific Ocean.
Seen on shorelines, on boats where they increase drag and on whales, barnacles are truly ubiquitous. Why? Because they are hardy and incredibly adept at eating opportunistically while avoiding being eaten. Defensively shelled, they are generally unpalatable. The work is not worth the morsel for most species. At the same time, barnacles can easily feed on whatever the current brings within reach of their feeding arms. In relative safety, barnacles feast and multiply.
The next time you see a barnacle or an entire white mass of encrusting rocks on the shore, take a pause to recognize the sheer adaptive ingenuity of the crustacean that comes in a mollusc-like shell.