In the spiny lobster (Panulirus interruptus) the prophenoloxidase is located in plasma not in haemocytes.

In the spiny lobster (Panulirus interruptus), unlike other crustaceans most of the prophenoloxidase (proPO) was detected in cell-free plasma (86.3%). In spite of its location, lobster proPO activating system has a similar activation mechanism to other crustacean proPO systems.