Hordes of land crabs occupied the Hawaiian Islands until they went extinct after the arrival of Polynesians some 1,000 years ago, says a Florida researcher who describes the species for the first time.

"If these land crabs were alive today, Hawaii would be a very different place," said researcher Gustav Paulay, with the Florida Museum of Natural History in Gainesville. "They certainly were major ecological players."

The species was unique to the Hawaiian Islands and was the most land-adapted crab in the Pacific, expanding further inland and to higher elevations than any other, Paulay says in a posting this week on the website PLoS ONE. The omnivores had a body about the size of a large hand and a pair of claws, the right bigger than the left.

Fossils of the species, Geograpsus severnsi, have been found on the major Hawaiian Islands for many years, but its identity was not clear. Researchers identified the crab by comparing physical characteristics with specimens from various collections.

Like other island land crabs, G. severnsi appears to have retained ties to the sea, where its larvae developed, Paulay says.

An analysis of the radiocarbon-dated specimens show they vanished soon after Polynesians colonized the Hawaiian Islands about 1,000 years ago, he says. Colonists brought novel predators to the islands, including lizards, rats, pigs, dogs and jungle fowl, which profoundly altered coastal and low-elevation habitats, he said.

The sister species to G. severnsi, Geograpsus grayi, still lives on many Pacific islands.