Anglerfish inhabit the deep sea, and for a century they baffled marine biologists. At first only female anglerfish were known; where the males were and what they looked like was a complete mystery. Then a parasitologist began studying the worm-like parasites generally attached to anglerfish females. What he found, instead of parasites, were anglerfish males — each undergoing a radical transformation. When a male anglerfish is tiny, he finds and attaches to a female. First his jaws dissolve and his bloodstream fuses with the female’s. Then his brain disappears and his guts shrink. Eventually he is little more than a testis, fertilizing the eggs of one female, for the rest of his life.
Clownfish families were made famous in ‘Finding Nemo,’ but real ones have more peculiar lives than the movie lets on. In a sea anemone where the clownfish live, the biggest fish is always a female, laying all the eggs. The next biggest fish is a functional male, fertilizing them. And lots of smaller clownfish are immature males. When the female dies or is eaten by a predator, the biggest male switches sex to become female. At the same time the biggest immature male grows into a functional male that can fertilize the eggs. This conveyor belt system of parenting assures a constant supply of baby Nemos.