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 Heterosaccus lunatus has revealed morphological differences between the male and female larvae, particularly the attachment organ of their antennules. The detailed features of the attachment organ (segment III) and segment IV for each sex are described and compared with those of other rhizocephalan cyprids, particularly Sacculina carcini, a reportedly closely related species. The absence of the large posterior sac from segment III in the H. lunatus male highlights the need for careful larval investigations on other sacculinid species. Settlement of female H. lunatus cyprids occurred on the gill lamellae of the host crab with the subsequent kentrogon stage taking the sacculinid form. The inclusion of H. lunatus in the Sacculinidae was therefore confirmed, based on the morphology of the cypris antennules and kentrogon.