By Megan Gannon, LiveScience News Editor: A male fish from Mexico has some fearsome genitalia.
Females of this species have evolved to have a big ball of tissue that blocks most of the genital pore. This means the female would have to deliberately allow the male to mate with her unless the male evolved a counter-response, Langerhans explained. The four-hooked genitalia could help the males overcome resistance and latch onto a female's genital pore and deposit sperm inside her. (Fertilization in the Gambusia genus takes place inside the female's body and she gives birth to live young.)