We describe the complete larval development of the pedunculated barnacle Capitulum mitella, using both light microscopy and scanning electron microscopy. This includes all six naupliar instars and the final cypris stage. Many previous accounts on the development of barnacle larvae suffer from a shortage in detail and habitually use terminologies that are either inconsistent or hard to compare with those used for other crustaceans. We therefore propose and use a new completely standardized terminology to enable comparison both within barnacles and with larvae of other crustaceans. Rather than a stage-by-stage description, our account follows changes in specific features during larval development. The morphological, ecological and phylogenetic significance of these characters is discussed. Special attention is paid to the feeding apparatus and how it may have undergone adaptive evolution in response to changes in the availability of food items through geologic time. C. mitella is universally agreed to be placed lower in the barnacle phylogeny than acorn barnacles (Balanomorpha), and fossil forms very similar to this species can be traced back to the Upper Jurassic. This makes C. mitella central to understanding the large-scale evolution within barnacles.
Capitulum mitella, Adaptive evolution, Feeding apparatus, Larval morphology, Standardized terminology
