In the category of “hats you probably shouldn’t wear to the Royal Wedding,” Phallostethus cuulong — a new species of fish discovered in Vietnam — has its genitalia on its head.
I really want that to mean that its penis is dongling from its forehead, like some kind of anglerfish/dildo hybrid, but in fact the genitals of P. cuulong sit near the throat. The female’s oviduct is located there, and the male has a complicated structure called the priapum, a kind of modified throat-pelvis housing the anus and the genitals — plus a jawlike structure intended for grasping the female’s head during copulation. Dude, no. Party foul.
It’s not clear why or how P. cuulong‘s junk snuck up around its neck, but one scientist theorized that head-to-head mating is more efficient for species that do their fertilizing internally. (A lot of female fish eject their eggs, which the male then fertilizes outside their body.) Clamped-on skull-humping might mean more fertilized eggs from each encounter.
Whatever the evolutionary reason, these fish seem to be doing all right. The areas where it lives in Vietnam have been undergoing rapid development, but the fish have proved tenacious — scientists have even found them in puddles on the side of the road. Maybe all threatened species should get genitalia hats.
New Genitalia-Headed Fish Is Evolutionary Mystery, National Geographic.
Get on your bike, Phallostethus cuulong, Scientific American.