Purple Crab Species Found in Philippines

Four new species of freshwater crab, bright purple in colour, have been discovered in the biologically diverse but ecologically-threatened Philippines, the man who found them said Saturday.

The tiny crustaceans were found in streams in remote areas of the Palawan island group, according to a team led by Hendrik Freitag, of Germany's Senckenberg Museum of Zoology.

Found only in small, lowland-forest ecosystems in the Palawan island group, most have purple shells, with claws and legs tipped red.

"They are semi-aquatic and hide in burrows at the stream bank, which are usually found under boulders and roots," said his paper published in the latest edition of the National University of Singapore's Raffles Bulletin of Zoology.

"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," said Freitag,
Their eggs hatch directly into juvenile crabs, and the creatures emerge at night to forage under water, Freitag added.

The biggest, Insulamon magnum, is just 53 millimetres by 41.8 millimetres while the smallest, Insulamon porculum, measures 33.1 by 25.1 millimetres.

Little is known about which creatures prey on the Insulamon crabs, though predators may snack on the crabs when the crustaceans molt, he added.

The two other new species were Insulamon palawense and Insulamon johannchristiani.

The four slightly differ from the first find, and from each other, in the shapes of their body shells, legs, and sex organs.

In Palawan, farmers are clearing tracts of forests, which dries up rivers and streams—a "major threat" for most freshwater species, including the crabs. Likewise, planned mining projects may harm water bodies in the region, particularly via pollutants.

After finding the new Philippine species, Freitag and students from Ateneo de Manila University plan to survey the Philippines' Mindoro Island (map), where many habitats are already pressured by mining.

"Many new species can be expected," he said.

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