Japanese and Vietnamese scientists have discovered a tiny species of fish that has its reproductive organs on its head, right behind their mouths. Dubbed Phallostethus cuulong, (penis chest) the males of the species uses its priapium and holds onto the female to deposit his sperm into the female’s urogenital opening, which is also located on the head, according to the paper “Phallostethus cuulong, a new species of priapiumfish (Actinopterygii: Atheriniformes: Phallostethidae) from the Vietnamese Mekong” published in Zootaxa.
The surface swimming fish, which can be found in shallow waterways of the Mekong River basin, is less than an inch in length and is for the most part, transparent in coloration. The scientists measured nine specimens and determined that Phallostethus cuulong is indeed a new species. According to the report, the little fish is the third species in its genus.
The complete paper can be found on the Zootaxa website in PDF format.