A toothy leech found in the noses of Peruvian swimmers has called attention to an unrecognized and gruesome branch on the tree of life.

Dubbed Tyrannobdella rex, "tyrant leech king," the pinkie-finger-sized bloodsucker has a single jaw, with teeth five times longer than those found in any other leech.

Described in a paper published April 14 in PLoS ONE, the first specimen was found by doctors in 1997 in the nose of a 6-year-old boy in San Martin, Peru. He had complained of headaches.

Another specimen was taken that year from a 16-month-old boy in Ayacucho, Peru. A decade later, a third T. rex was taken from the nose of a 9-year-old Peruvian girl who felt a "sliding" sensation in her nose. All had bathed frequently in Amazonian streams.

The habit of invading an orifice and feeding on mucous membranes is known as hirudiniasis, and had been seen in a variety of leech species in the Middle East, Africa and Asia. Scientists assumed these species to be unrelated, regarding their feeding habits "only as a loathsome oddity and not a unifying character for a group of related organisms," wrote the researchers.

But when they took a closer look at these species, the researchers noticed anatomical similarities. Genetic comparisons supported the observation. T. rex and the other mucous-membrane feeders actually belong to a single group. DNA differences between them, combined with known mutation rates, suggest a last common ancestor about 200 million years ago, when dinosaurs rose to Earthly dominance.

An ancestor of T. rex may have swum up the other T. rex's nose.

Images: From PLoS ONE: 1. Close-up of the T. rex jaw at left, and its front sucker at right.

2. Examples of other mucous-membrane–feeding leech species.

See Also:

Citation: "Tyrannobdellarex N. Gen. N. Sp. and the Evolutionary Origins of Mucosal Leech Infestations." By Anna J. Phillips, Renzo Arauco-Brown, Alejandro Oceguera-Figueroa, Gloria P. Gomez, Maria Beltran, Yi-Te Lai, Mark E. Siddall.

Brandon Keim's Twitter stream and reportorial outtakes; Wired Science on Twitter. Brandon is currently working on a book about ecological tipping points.