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Image Gallery: Weird 'Penis Head' Fish

Introducing Phallostethus cuulong

(Image credit: L.X. Tran, Zootaxa)

The male of this new species of fish sports its sex organ on its chin, though it looks nothing like the members on humans and other mammals.

Penis-head breakdown

(Image credit: L.X. Tran, Zootaxa)

Called the priapium, the sex organ includes two bony attachments, a rod-like structure (toxactinium) and a serrated hook (ctenactinium), used to clasp the female while mating.

Male and female, side by side

(Image credit: L.X. Tran and K. Shibukawa, Zootaxa)

These freshly collected male (A) and female (B) specimens of Phallostethus cuulong were found in Vietnam's Mekong Delta.

The fish is also poop-headed

(Image credit: L.X. Tran and K. Shibukawa, Zootaxa)

Not only are the male fish's sex parts at its head, but also its anus.

The female's parts are backwards, too

(Image credit: L.X. Tran and K. Shibukawa, Zootaxa)

The female Phallostethus cuulong has a genital opening and an anus under her throat. Fertilization takes place inside the female's body — a rarity among fish. The male's hook is probably designed to clasp onto her to ensure successful fertilization while mating.