Image Gallery: Weird 'Penis Head' Fish

Introducing Phallostethus cuulong

Penis-head breakdown

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

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

The female's parts are backwards, too

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.

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Megan has been writing for Live Science and Space.com since 2012. Her interests range from archaeology to space exploration, and she has a bachelor's degree in English and art history from New York University. Megan spent two years as a reporter on the national desk at NewsCore. She has watched dinosaur auctions, witnessed rocket launches, licked ancient pottery sherds in Cyprus and flown in zero gravity. Follow her on Twitter and Google+.