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The images show a female Leatherjacket Louse, Ourozeuktes bopyroides, that was removed from a Yellow-finned Leatherjacket.
The fish was collected by Australian Museum staff diving at a depth of 10 m, Balls Head Bay, Sydney Harbour, May 2001 (AMS I.40836-008).
The Leatherjacket Louse is a species of parasitic cymothoid isopod that occurs in Australia's temperate marine waters.
It burrows its way through the body wall of the fish until it enters the body cavity. There it feeds on the host's tissues often in the region of the liver.
The Leatherjacket Louse is never totally concealed inside the fish. The posterior part of the louse always projects through a slit in the body wall.
The adult female Leatherjacket Louse like the individual in the images grows very large and never leaves the host.
- Hale, H. M. 1929. The Crustaceans of South Australia. Harrison Weir - Government Printer, Adelaide. Pp. 380.