E. covertus is found on bark and leaves of the grey mangrove Avicennia marina, H. foliorum is found on leaves and H. popeiana is found on bark. 7655 barnacles were collected from two sites at Woolooware Bay from winter 1987 to summer 1989. Reproductive and external features in E. covertus differed depending on the substratum on which it lived; reproductive output was greater on leaves than on bark. The genus Hexaminius has been classified elsewhere as two species on the basis of external features and reproductive differences of adults, larval development and larval setation; however, the adults were living on different substrata. A detailed study of larval and juvenile stages of Hexaminius in the field showed no differences in external features until juveniles were one month old and no differences in the time taken to rear cyprid larvae. This suggests that Hexaminius should not continue to be divided into two species.