Meet Sacculina carcini – a barnacle that makes a living as a real-life body-snatcher of crabs. Unlike most barnacles that are happy to simply stick themselves to a rock and filter food from the water, Sacculina and its kin have evolved to be parasitic, and they are horrifyingly good at it.
The microscopic larva of Sacculina seeks out an unsuspecting crab using specialised sensory organs. It then settles on a part of the crab where its armours is most vulnerable, usually on the membrane at the base of one of the crab's hair (called a setae).
The larvae then transforms itself into a kind of living hypodermic syringe (called a kentrogon). This syringe stabs the base of the crab's hair and injects the next stage of the parasite – a microscopic blob called the vermigon – into the crab's bloodstream. This blob will eventually grow into a parasite that takes over the crab's entire body.
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