Sex gets even stranger for some barnacles. The barnacles in (b) and (d), top and bottom right, are like most barnacles, living in happy (I assume) clumps of hermaphrodites, sexing away with each other in reciprocal fashion.
The barnacle in (a) top left, is a lone hermaphrodite. For reproduction, it depends on wee little dwarf males, no bigger than a pinhead. The barnacle species in (d), bottom left, has separate males and females, one of the only barnacle species that does. Here all the males are dwarf, and only the female is large.
And this doesn’t even get into the weirdness that is parasitic barnacles, who infect crabs. They take up residence in the female crab’s reproductive system and sterilize her. Then they take on the form of a crab egg sac, typically carried under the crabs abdomen, so the female crab cares for and protects the parasites as though they were her own young. If they infect a male crab, they not only sterilize him, they alter his behavior so that he behaves like a female, caring for a fake egg sac that is actually a breeding pair of parasites.
And now you all know why I would eat a thousand cows before I ate one fucking thing from the ocean.