Look Inside a Barnacle: Video Proof That These Rock-Like Shells Are Alive

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Do barnacles feel pain or possess a brain?
Barnacles do not have a centralized brain like vertebrates or cephalopods. Instead, their nervous system consists of a supraesophageal ganglion connected to a ventral nerve cord and paired peripheral ganglia. They possess sensory bristles and photosensitive eye spots that register light, shadow, touch, and chemical concentrations, allowing rapid reflexive protection against predators.

Are barnacles related to clams or crabs?
Barnacles are crustaceans, making them direct relatives of crabs, lobsters, krill, and mantis shrimp. While their hard calcium carbonate shells mimic clam or mussel valves, their internal anatomy, including jointed limbs, chitinous carapaces, segmented bodies, and larval stages, places them firmly inside the phylum Arthropoda.

How do barnacles reproduce if they cannot move to find a mate?
Most barnacle species are simultaneous hermaphrodites, possessing both male and female reproductive organs. Because adults cannot detach from their substrates, they rely on an exceptionally long, flexible organ capable of extending up to eight times their shell length to fertilize neighboring individuals within their dense colonies.