Four new-to-science crab species have been discovered in The Philippines, on the island of Palawan, and one of them has a beautiful purple shell.
The so-called Insulamon palawanese crab may use its uniquely colored shell to help identify its own kind.
Crabs can discriminate colors. Therefore, it seems likely that the purple coloration is a function for their social behaviour, like when choosing mates. Though the particular violet coloration might just have evolved by chance, and may not necessarily have a very specific function or reason aside from being a general visual signal for recognition, for other crabs of the species.