The presence of embryos in the mantle cavity ofCatomerus polymerus, Chamaesipho tasmanicaandChthamalus antennatuswas monitored over a two year period.C. polymerusandC. tasmanicashow a clearly defined breeding season spanning late autumn, winter and early spring.C. antennatusbreeds more continuously throughout the year, with a decline in breeding during the winter. The larval stages ofC. polymerus, C. tasmanicaandC. antennatusare described from larvae reared in the laboratory. Morphological differences allow each larval stage of the three species to be distinguished without difficulty. Unique larval features permit identification to superfamily, family and genus. The similarities of chthamaloid nauplii to those of lepadomorphs and verrucomorphs and their differences from the nauplii of other balanomorphs are discussed. Larval evidence supports the view that the chthamaloids are related more closely than other balanomorphs to the lepadomorphs, and that the coronuloids and balanoids share a comon derivation from the chthamaloids.