Pictures: New Purple Crab Species Found

Pretty in Purple
Photograph courtesy Hendrik Freitag
A purple crab stares down the camera in the Philippine island of Palawan (map) in an undated picture. The colorful crustacean, dubbed Insulamon palawanense, is one of four new species in the Insulamon genus described in a recent study.
The crab's brilliant hues may simply help the species recognize its brethren, said study author Hendrik Freitag, of the Senckenberg Museum of Zoology in Dresden, Germany.
"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, whose study was published in February in the Raffles Bulletin of Zoology.
(Related pictures: "A World of Crabs From One Tiny Island.")
Freitag described the four new crabs—each between about an inch (2.5 centimeters) to 2 inches (5.3 centimeters) wide—from museum specimens and individuals collected during two field surveys in Palawan. Only one other species, I. unicorn, is already known in the genus, and it was identified in 1992.
—Christine Dell'Amore
Published April 18, 2012
Freshwater Crab
Photograph courtesy Hendrik Freitag
A male I. palawanense is seen on a rock in Palawan. The species is widespread throughout the Philippine island, unlike the other three newfound species, which are restricted to small home creeks or rivers.
Including the previously known I. unicorn, all five Insulamon species are exclusively freshwater creatures, spending their days burrowing in muddy holes and emerging at night to feed.
That's an unusual life cycle for a crab—most of the world's known crabs migrate to the sea at some point to spawn, Freitag said.
(See pictures: "Crab Swarms Overtake Island—Mystery Solved.")
Published April 18, 2012
Dominant Male
Photograph courtesy Hendrik Freitag
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.")
Published April 18, 2012
Purple Shield
Photograph courtesy Hendrik Freitag
The deep purple of an I. johannchristiani female's carapace is seen from above.
Whatever their color, Insulamon carapaces are strong and hard, which may prevent the crabs from getting battered by river rocks, Freitag said.
The crabs' carapaces also appear swollen, which is due to enlarged gill chambers that allow the crabs to stay on land longer.
(See "She-Crabs Are World's Pickiest Daters.")
Published April 18, 2012
One Big Crab
Photograph courtesy Hendrik Freitag
The new crab species I. magnum (pictured) was named for its relatively large size of about 2 inches (5.3 centimeters) wide—magnum means "big" in Latin.
Little is known about which creatures prey on the Insulamon crabs, though predators may snack on the crabs when the crustaceans molt, he added.
"This might be the most dangerous time in their lives—their shells are very soft."
(See picture: "Crab's 'Fighting Claw' Often Fake.")
Published April 18, 2012
Crab Under Threat?
Photograph courtesy Hendrik Freitag
Most Insulamon crabs—including I. magnum, seen above—are more threatened than other freshwater crabs because they're confined to specific creeks and small rivers, Freitag said.
Also, because the crabs live in or close to running water their whole lives, "they cannot just escape or migrate via the ocean or dry land to other places when their original habitat [is] destroyed," he said.
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.
(Read more about freshwater threats.)
Published April 18, 2012
Pregnant Crab
Photograph courtesy Hendrik Freitag
A view of the underside of an I. magnum female reveals the eggs she's carrying.
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.
Published April 18, 2012
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Photograph courtesy Stephanie Stone, California Academy of Sciences
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1 comments

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Neesy Tompkins

I found one of these in my front yard this evening. Close to a drainage ditch, and quite aggressive. Due to the drought I wondered if he was searching for water. Gorgeous purple hues.

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