Scientists unravel mystery of echidnas' bizarre 4-headed penis - Livescience.com

Much about this group remains a mystery, the study researchers said.

"Exactly how echidnas do this has always been a mystery," the study researchers said in a statement.

"Ejaculated semen samples contained bundles of up to 100 sperm that are joined at the tip of their heads so they form a sphere-like shape," Jane Fenelon, lead author of the study and a reproductive biologist at the University of Melbourne, told Live Science.

To understand more about how echidna penises work, Fenelon's team turned to short-beaked echidnas (Tachyglossus aculeatus) at a wildlife sanctuary in Australia.

But luckily for the researchers, the euthanized echidnas' penises are still in good enough shape to study, Fenelon said. .

Researchers took the euthanized echidnas and created 3D models of their penises using specialized CT scans.

"This meant we could create a 3D model of the whole echidna penis and its important internal structures in order to see how it operates," the researchers wrote.

Mammalian penises consist of two main types of erectile tissue — the corpus cavernosum and the corpus spongiosum.

Both tissues fill with blood during an erection, but the role of the corpus cavernosum is predominantly to provide a rigid structure to the penis, whereas the corpus spongiosum keeps the urethral tube open to allow sperm to pass through. .

But in short-beaked echidnas, the cavernosum was merged while the spongiosum remained separate.

This separate spongiosum tissue is what allows echidnas to erect each half, or pair of heads, independently from the other, the researchers said