The Crab with Lopsided Sex Organs

A new-to-science, completely unique, and kind of weird crab has been found by researchers at the University of the Ryukyus.

The crab, named Mabui calculus by scientists, is small, only 6mm wide and lives right by the coast on the island of Okinawa in the Japanese archipelago.

The crab belongs to the Xanthid family, which are most diverse in tropical environments and are often highly poisonous. Not only are they super dangerous, but cooking them does not remove their poison and there is no known antidote.

There are over 7,800 species of Xanthid crab, but only one this one exhibits these asymmetrical sexual organs.

It has taken over ten years of research to properly identify whether this asymmetry was natural or a mutation. However the study shows that this is just how these crabs roll.

Peter Ng, leading crustacean expert writes “When we took a closer look at these crabs, we found the males and females crabs have markedly asymmetrical male gonopods and female vulvae—one member of each pair was normal while the other was strongly reduced. And they form matching pairs,”

He continues, “The right male gonopod is long and well developed, while the left one is much smaller. The left female vulva is large and round, while the right one is lost in most of females. This is the only way the crabs can mate effectively. The evolution of asymmetrical reproductive parts is not known for any crab, and this is truly amazing in nature.”

Pretty cool right?

P.C: Tohru Naruse