The first complete larval development of the parasitic barnacle from the genus Briarosaccus

The complete larval development of Briarosaccus hoegi (Rhizocephala: Peltogastridae), including five naupliar and one cypris stages, is described and illustrated using SEM. The present study confirms that all rhizocephalans have 5 naupliar stages during the larval development. The larvae of B. hoegi are almost twice as large as the larvae of other rhizocephalans. Male larvae are considerably larger than female ones, their sizes never overlap. Larvae of B. hoegi show the peltogastrid type of development. Late male nauplii have large frontal protrusions, absent in female larvae. The second antennular segment in male nauplii is definitely longer than that in female larvae. These two characters indicate a distinct sexual dimorphism between male and female nauplii of rhizocephalans. Nauplii and cyprid of B. hoegi have pigmented nauplius eyes and show positive phototaxis. There is no correlation between the presence of a flotation collar and a nauplius eye in rhizocephalan larvae. The attachment disc in the female cyprid has a flap-like extension at the posterior margin. The attachment disc in male and female cyprids possesses two sensory setae. The large aesthetasc in the male cyprid is unilobed. The subterminal aesthetasc in female cyprid terminates into a single long filamentous process. A short postaxial sensory seta on the second antennular segment is completely reduced in the male cyprid. The nauplii and cyprids of B. hoegi and Briarosaccus tenellus are very similar. Our study confirms that the genus Briarosaccus consists of two cryptic species.