The cypris larvae of the rhizocephalan barnacle Heterosaccus lunatus with particular reference to antennular morphology

SEM investigation of laboratory-reared cyprids of the parasitic barnacle He terosaccus lunatus has revealed morphological differences between the male and female larvae, particularly the attachment organ of their antennules. T he detailed features of the attachment organ (segment III) and segment TV f or each sex are described acid compared with those of other rhizocephalan c yprids, particularly Sacculina carcini, a reportedly closely related specie s. The absence of the large posterior sac from segment III in the H. lunatu s male highlights the need for careful larval investigations on other saccu linid species. Settlement of female H. lunatus cyprids occurred on the gill lamellae of the host crab with the subsequent kentrogon stage taking the s acculinid form. The inclusion of H. lunatus in the Sacculinidae was therefo re confirmed, based on the morphology of the cypris antennules and kentrogo n.