Charles Darwin published four volumes on barnacles.
These works were his major studies of the crustacean group Cirripedia, commonly known as barnacles. Published between 1851 and 1854, they comprised two volumes on living barnacles and two on fossil forms. The monographs provided detailed descriptions, classifications, illustrations, and anatomical observations aimed primarily at specialist readers.
Darwin’s interest began with an unusual barnacle he collected during the voyage of HMS Beagle near the Chonos Archipelago in 1835. Years later, sustained microscopic study of barnacle structure became an important part of his scientific work. The project lasted about eight years and helped establish his reputation as a careful comparative biologist.
The number is sometimes confused because the works are also discussed as one large barnacle monograph or as separate titles covering living and fossil groups. Counting the published volumes, however, gives four. The research also influenced Darwin’s thinking about variation, classification, and the boundaries between species.