A new species of Archaeobalanidae barnacle is described from the late Miocene and early Pliocene of Santa Maria Island (Azores). Samples were collected primarily from outcrops at Malbusca and “Pedra-que-Pica”. Zullobalanus santamariaensis sp. nov. is endemic to the Azores archipelago and until the discovery of this material, the genus was known only from the Southern Hemisphere. For such a long-range distribution we assume a combination of planktotrophic larval development, sea-surface oceanic currents and transport by cetaceans. This study endorses the elevation of the subgenus Zullobalanus to generic level.

The reproductive biology of Megabalanus azoricus (Pilsbry), the commercially exploited barnacle in the Azores, was studied in an attempt to provide the scientific basis for the sustainable management of this heavily exploited regional marine resource. Both the Ospar Commission and WWF have expressed concern for this species, considering it at risk and in urgent need for scientific study. Barnacles were collected every month from shallow water (≈3 m depth) around São Miguel Island from October 2004 to September 2005. Individuals were measured and gonads processed for histology and analysed with a stereological method. M. azoricus has a hermaphroditic reproductive system with separate gonads and it was possible to describe the various stages of gametic maturation in both. Data on fertility were also obtained by egg counts and calculation of the Gonadosomatic index (GSI). Throughout the year, some specimens of M. azoricus can be found that rare mature, but two reproductive peaks were observed, one in January and a smaller one in July. A strong positive correlation between GSI and environmental factors such as photoperiod and water temperature was observed.

Re-examination of Megabalanus azoricus from the Azores revealed previously unknown morphological features. Examination of more exemplars also confirmed the description made by Pilsbry in 1916. Morphological features are herein described (e.g. true tergal spur) and morphometric relations are established for the first time, providing a significant contribution towards the management of this important Azorean seafood resource.