Status:
Native
ID Difficulty
Identification
This species is an internal parasite of barnacles, specifically occurring in the mantle cavity of Semibalanus balanoides (Linnaeus) and Austrominius modestus (Darwin). Being protandrous hermaphrodites, males of the species infect the barnacle, becoming female and castrating the host. The adults females reach up to 8 mm, though they can be considerably smaller than this. During their development, they lose obvious isopod characteristics, becoming sac-like, enlarged and yellow with two or three lobes on each side. The head and front pereopods remain, though in a reduced form as a small conical projection towards one end of the individual, whilst a small conical posterior region with traces of somites may also be observable.
Males and, especially, females of the species may be found in barnacle scrappings and identification should be confirmed by close examination using a binocular microscope. Arnott (2001) recommends removal of the barnacles using a scalpel immediately into a preserving solution to immobilise the free-moving males.