Yes. Barnacles are living marine animals — specifically crustaceans related to crabs, lobsters, and shrimp, not rocks or empty shells. NOAA Ocean Service explains that adults secrete calcium plates around their bodies and feed by combing the water with feather-like appendages called cirri for microscopic organisms.
Of more than 1,400 barnacle species worldwide, the common acorn forms cement themselves to rocks, pilings, ships, and even whales. They open their shell “door” when submerged to feed and close it at low tide to keep from drying out.