Larvae of two parasitic barnacles, Parasacculina pilosella (Van Kampen et Boschma, 1925) (Rhizocephala: Polyascidae) and Sacculina pugettiae Shiino, 1943 (Rhizocephala: Sacculinidae) studied by scanning electron microscopy.

The complete larval development of Parasacculina pilosella (Van Kampen et Boschma, 1925) and Sacculina pugettiae Shiino, 1943 including five naupliar stages and one cypris stage is described and illustrated using SEM. P. pilosella and S. pugettiae have a sacculinid type of development. Nauplii possess a naupliar eye, short frontolateral horns with terminal processes, and a ventral process between the furcal rami. Larvae lack a flotation collar, seta 6 on the antennule and a seta on the antennal basis. Cyprids have a nearly straight LO2. Breakage zone and a spinous process are present only in male larvae. Nauplii of the two species differ by the morphology of the furca: in P. pilosella, the furcal rami are longer and not drowned into cuticular sockets. Naupliar antenna of S. pugettiae has a lateral seta on the endopod which is lacking in P. pilosella. Dorsal head shield setae 1 and 2a are present in S. pugettiae nauplii and not found in P. pilosella larvae. In P. pilosella, all dorsal setae have subterminal pores, whereas in S. pugettiae, pores of the setae 2 are shifted proximally. It is possible that the presence/absence of setae 1 and 2a is the distinctive feature of nauplii of the families Sacculinidae and Polyascidae.