Large Insulamon males—such as this I. johannchristiani, another of the newfound species—sport a reddish color, possibly to signal their power, Freitag said.
Smaller, less dominant Insulamon males and females are purple, he noted.
Crabs in the Potamidae family, to which the new species belong, are found around the world, and in most places the crustaceans look fairly similar, he added.
"This probably indicates their body shape is a perfect adaptation for river habitats," he said.
For instance, the carapace—or back shell—of a Potamidae crab is rounder and smaller than in other freshwater crabs, making it easier for the animal to burrow.
(See "'Yeti' Crabs Farm Food on Own Arms—A First.")