The song Barnacle Bill the Sailor is not far from the truth in the case of pelagic barnacles. It is a common sight to see shore barnacles, the pelagics' cousins, stuck on rocks without hope of ever experiencing any different kind of habitat. In contrast, pelagic barnacles attach from everything as seriously solid as oil tankers to flimsy, disintegrating pieces of driftwood.
How do these rock-like creatures end up in such a variety of marine movers from ships to things that drift? Their larvae stage is the key. After first hatching, barnacles are swimming shrimp-like creatures. They can follow chemical trails sent out by adult barnacle communities to join good habitats where barnacles already live. When they arrive, they hit the surface head-down and begin gluing themselves upside-down to the surface. This barnacle glue is a super-strong substance that resists acid and hardens quickly in water.
To eat, pelagic barnacles reach out with feathery legs to collect whatever is drifting by, or in the case of the shipping barnacles, whatever is zipping by.
Even though barnacles look like mollusks, soft-bodied animals with shells, they are actually crustaceans just like crabs, shrimp and lobsters. Inside their shells, they have soft-jointed bodies and feathery legs, not like the globular bodies of mollusks.
The pelagic barnacles above were photographed at the Monterey Bay Aquarium. To see them in a natural habitat, you could check on the sides of boats. Or inspect driftwood on local beaches. I read one account online where someone found driftwood with barnacle shapes and then placed the whole piece into a bucket of water. Magically the barnacle legs started waving like leaves around the piece of wood.
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