The family Scalpellidae is a large family of barnacles containing ca. 200+ nominal species. These barnacles inhabit a wide range of depths, although most species live in the deep sea. These species are dioecious (with large females and dwarf males) or androdioecious (with large hermaphrodites and dwarf males), with one or more dwarf males settling in a specific location (the receptacle) in the larger individuals. We studied the reproductive ecology of six dioecious scalpellid barnacle species in the deep sea, which differ in size and habitat depth. Intraspecific analyses revealed that there was a positive relationship between female size and egg number in all the species, but no significant relationship existed between female size and egg size. No trade-off was detected between the size and number of eggs in a brood. Moreover, there was a positive relationship between female size and the number of dwarf males in three species that possess receptacles that carry more than one male. On the other hand, interspecific analyses suggested that female size was positively related to egg size, egg number, and the number of dwarf males. Considering the large variety of reproductive traits and the many species in this group, further research is needed to elucidate how reproductive traits have evolved in scalpellids.
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