Parasitic Barnacle on a Crab

This swimming crab (Liocarcinus holsatus) has a parasitic barnacle rooted in its reproductive system. This invasion cuts off all reproduction for an infected crab and can even cause a male crab to change behavior — males don't normally take care of crab eggs, but the infected male will take care of the barnacle as if it is a brood of eggs. Read more about other parasites that you can find in marine organisms.