The sexuality of large (non-dwarf) individuals and the characteristics of eggs, larvae and dwarf males were investigated in the pedunculate barnacle Scalpellum stearnsii. All 103 large individuals collected in this study were not hermaphrodites but females. The major length axis of the egg was on average 0.50 mm, which was larger than that in most thoracican barnacles with planktotrophic larvae. The larvae hatched as nauplii and metamorphosed into cyprids without feeding (i.e. lecithotrophic development). There was a positive relationship between body weight and egg mass weight in ovigerous females. The number of males attached per female ranged from 0 to 35 (average: 5.9) and there was a positive relationship between the number of males and female body weight. The distribution of dwarf males was skewed significantly towards the lower part of the occludent margin, which is near the fertilization site.
