Description: 

This parasite makes male crabs think that they’re pregnant females. 

Transcription: 

Most of us know barnacles as those small, shelled creatures you find at the 

beach attached to rocks and piers. But, there’s one species of barnacle with

a very different sort of life cycle. It’s a parasite that castrates crabs and turns

them into barnacle baby-making machines. I’m Anna Rothschild, and this is

Gross Science. So this parasitic barnacle is called Loxothylacus panopaei,

and it starts out its life just like most barnacles do—as a free-swimming 

creature looking for a home. And, home for this particular parasite is inside 

of a mud crab. When a young female barnacle finds a mud crab and let’s 

say it’s a male mud crab, though they infect females as well) she undergoes

a transformation, losing her eyes and legs. Then, she injects herself into the

crab’s circulatory system. Once inside she starts forming a root system 

throughout the crab’s body, castrating him in the process. Soon, a sac starts

poking out from the crab’s abdomen. This is an “externa,” the reproductive

organs of the adult female barnacle. The externa attracts male barnacles,

and when a male arrives he injects his own cells into the sac, which grow 

into a testicle-like structure. In fact, the adult male barnacle exists only as 

a testicle, fertilizing the female barnacle’s eggs.

Questions: 

1. What are barnicles? 

2. What kind of parasites do male mad crabs have? 

3. Discuss the life cycle of these parasitic barnacles.