Four new species of crab have been discovered in the Philippine island of Palawan. And one of the crabs truly stands out with its unusually bright purple shell.

National Geographic reports that the Insulamon palawanese may use its uniquely colored shell to help identify its own kind.

"It is known that crabs can discriminate colours. Therefore, it seems likely that the colouration has a signal function for the social behaviour, e.g. mating," Hendrik Freitag of the Senckenberg Museum of Zoology in Dresden, Germany told AFP.

"The particular violet coloration might just have evolved by chance, and must not necessarily have a very specific function or reason aside from being a general visual signal for recognition," Freitag told National Geographic. Freitag's report on the new species of crabs was published in the Raffles Bulletin of Zoology.

[Slideshow: Newly discovered purple crabs]

Despite the big news, the newly discovered crabs are quite small in stature, each from about an inch to two inches wide.

While many species of crab are known by their red rust hues, some differently colored crab species are quite popular around the world, perhaps most notably the Chesapeake blue crab.

Freitag said the purple crabs likely have several natural predators, including some humans in remote areas. But he said the greatest threat to the species is ongoing forest clearing for farming, mining and home building.

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