‘The male deep-sea anglerfish is much smaller than the female and doesn’t have a lure. He’s interested in mating, not fishing. He uses his giant eyes to look for a suitable female, and his enormous nostrils to sniff out her pheromones. Having found her, he latches on to her with his teeth and then starts to disappear. Scales, bones, blood vessels all merge into those of the female. After a few weeks all that’s left of the male are the testes hanging of the female’s side, supplying her with sperm. Females have been found with eight testes attached to their sides.
In some species, if the male fails to find a female, then he will eventually turn into one himself and grow massively in size.’
– Lloyd. J., Mitchinson. J. 2007. The QI Book of Animals London, Great Britain: Faber and Faber (2009) p. 7