A barnacle, or any member of the family Balanidae, which are small crustaceans that attach to rocks, ships, and other surfaces in water.
From Greek 'balanos' (acorn), because barnacles resemble acorns in shape. The scientific family name Balanidae uses this same Greek root to classify these marine creatures.
Barnacles are actually little shrimp-like creatures hiding inside acorn-shaped shells—Charles Darwin studied them obsessively for eight years, and his detailed work is still the foundation for barnacle science today.
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