An article Wednesday in the journal PLoS One named Paedophryne amauensis as the world's smallest animal with a spine.

The adult frogs are about three-tenths of an inch long, and a millimeter or so smaller than a carp found on the Indonesian island of Sumatra. The frogs are so small that Louisiana State University herpetologist and environmental biologist Christopher Austin had to enlarge close-up photos to describe them.

But the males of a species of deep-sea anglerfish are about 2 mm smaller, said University of Washington ichthyologist Theodore Pietsch, who described them in 2006. The males don't have stomachs and live as parasites on 1.8-inch (4.57-centimeter)-long females.

Austin discovered the tiny frogs — along with another small frog species — in August 2009 while on a trip to Papua New Guinea to study the extreme diversity of the island's wildlife. He said he knew about the anglerfish but felt that average species size made more sense for comparison.

Steven J. Beaupre, a University of Arkansas scientist and president-elect of the American Society of Ichthyologists and Herpetologists, said many vertebrates have males and females of very different sizes, "so it is reasonable that the world's smallest vertebrate may end up being either the males or the females of some specific fish or amphibian species."