In the human world they’re called "lead guitarists"

Because angler fish are so sparsely populated throughout the vast

millions of cubic miles of ocean, chance mating encounters between

males and females would be unlikely. In fact, when deep-sea anglers

were first brought up in trawls they puzzled scientists because they

were all females. Then someone noticed small “growths” on the female

that turned out to be males.

When a tiny male meets a female he bits

into her flesh and literally fuses with her body. Like the linking

together of web sites on the Internet, the two blood supplies also fuse

together so that the male obtains nutrients and oxygen from the female.

Without any need for most of his organ systems, such as eyes and

digestive organs, the male’s body degenerates into essentially a pair

of sperm-producing testicles. Thus the female essentially becomes a

hermaphrodite with up to six or more of these tiny male parasites

attached to various parts of her body.

Although functionally bisexual,

the eggs and sperm come from genetically distinct parents, thus

providing vital genetic variability through meiosis and genetic

recombination. As a functional hermaphrodite she can have sex any time

or place, without worrying about meeting a male in the dark abyss of

the ocean. Clinging to her body like minute, blood-sucking parasites,

the males have little interaction with the female, except to fertilize

her eggs with sperm.