Cartilaginous fishes, like sharks and rays, are blessed with something called “claspers,” dual sperm-releasing tubes jutting from their pelvic fins. Why two? Thanks to a recent study published in the journal Nature Communications, we now know more about the sea creatures’ mysterious double dongs.


Many animals, including humans, have a gene called Sonic hedgehog (Shh)—named by discoverers who were clearly twisted Sega fans. The gene promotes cell growth that leads to the development of an organism’s body. Now researchers at the University of Florida have confirmed that prolonged exposure to Shh causes the growth of penis-like appendages in cartilaginous fish, after completing an experiment focusing on skate embryos.

In an experiment, researchers found that the presence of Shh caused claspers to appear late in male pelvic growth. The gene expressed for approximately four weeks longer in males than females. The team confirmed Shh was vital in the process by injecting carrier beads filled with cyclopamine, an Shh inhibitor, into male skate embryos. Lo and behold, clasper growth was stunted. Even wilder, pumping female embryos with extra Shh caused those skates to start developing twin penises of their own.


The study confirmed the biological process that cause cartilaginous fish to have claspers, but it still doesn’t quite answer what the second member is for—especially since only one clasper is used while mating. The evolutionary advantages are still unknown, as reproductive behavior in sharks hasn’t been widely observed.

Shh is responsible for the development of all kinds of body parts, like brains, spinal cords, and limbs. It’s also responsible for ensuring that eye-developing cells split up and form two separate eyes.

And now, I won’t be able to stop associating Sonic with shark schlongs.

Read the full study at Nature Communications via Science



Image via dconvertini, Creative Commons