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Nasty leech dubbed “T. rex” of its kind

April 14, 2010
Courtesy American Museum of Natural History
and World Science staff

The newest T. rex has just one row of teeth, and they are huge for a leech—which is what this re­cently dis­cov­ered an­i­mal is.

Sci­en­tists have named the slimy crit­ter Ty­ran­nob­della rex, Lat­in for “ty­rant leech king,” in hom­age to the si­m­i­larly named di­no­saur Ty­ran­no­saur­us rex (ty­rant liz­ard king).

Inside the mouth of Ty­ran­nob­del­la rex. (Credit: Phil­lips et al.)


The leech is­n’t the only ad­di­tion­al crea­ture to have joined that fa­mous rep­tile in re­ceiv­ing a mon­i­ker whose com­mon ab­brevia­t­ion is T. rex.

But it may well be the gross­est. 

The blood­suck­er was dis­cov­ered three years ago in Peru when it was plucked from in­side the nose of a girl who had tak­en a dip in a riv­er, re­search­ers said. 

They spec­u­lat­ed that the leech might make a liv­ing by tor­ment­ing aqua­t­ic mam­mals in si­m­i­lar fash­ion, and that its fore­bears may have even vic­tim­ized the dino­saurs in such a way. “Some an­ces­tor of our T. rex may have been up that oth­er T. rex’s nose,” said Mark Sid­dall, cu­ra­tor in in­ver­te­brate zo­ol­o­gy at the mu­se­um, one of the re­search­ers who has ana­lyzed the crea­ture. 

The 4.45 cen­ti­me­ter (al­most 2 inch) an­i­mal has been now clas­si­fied as a new spe­cies that lives in the re­mote parts of the Up­per Am­a­zon.

The spe­cies, de­scribed in the re­search jour­nal PLoS One, has led to re­vis­ing the family tree of a group of leeches that has a hab­it of feed­ing from body ori­fices of mam­mals. “Be­cause of our anal­y­sis of mor­phol­o­gy [body form] and DNA, we think that Ty­ran­nob­della rex is most closely re­lat­ed to an­oth­er leech that gets in­to the mouths of live­stock in Mex­i­co,” said An­na Phil­lips, a grad­u­ate stu­dent af­fil­i­at­ed with the Amer­i­can Mu­se­um of Nat­u­ral His­to­ry and an au­thor of the pa­per.

“We think the leech could feed on aquat­ic mam­mals, from their noses and mouths for ex­am­ple, where they could stay for weeks at a time.”

Dis­cov­er­ies of new leech spe­cies are not un­com­mon. Al­though there are 600 to 700 spe­cies of de­scribed leeches, it is thought that there could be as many as 10,000 spe­cies in ma­rine, land and fresh wa­ter en­vi­ron­ments world­wide. 

The lit­tle T. rex underwent analysis after being brought to the at­ten­tion of Sid­dall. He re­ceived a spec­i­men col­lect­ed by Renzo Arauco-Brown, a doc­tor from the Uni­ver­si­dad Pe­ru­ana Cayetano He­re­dia in Li­ma, Pe­ru, who worked at a clin­ic in Chan­chamayo prov­ince. 

Sid­dall said he im­me­di­ately rec­og­nized the crea­ture as a new spe­cies. His stu­dent Ale­jan­dro Oceguera-Figueroa de­scribed its weird for­m—a sin­gle jaw with eight very large teeth, and ex­tremely small gen­i­ta­lia. Two ear­li­er cases from 1997 were re-dis­cov­ered from dif­fer­ent clin­ics in the west­ern Am­a­zon, one from La­mas prov­ince and the oth­er from Yochegua prov­ince.

The leech was un­ique enough that it was not only clas­si­fied as its own spe­cies, but its own ge­nus, a larg­er ev­o­lu­tion­ary group­ing that may in­clude one more spe­cies.

This anal­y­sis has led to a re­vi­sion of the ev­o­lu­tion­ary rela­t­ion­ships among sev­er­al leech fam­i­lies, ac­cord­ing to Phil­lips and col­leagues. They de­scribe the spe­cies as most closely re­lat­ed to Pin­tobdella chi­a­pasen­sis, a leech from Chia­pas, Mex­ico, that infests ta­pirs and, less often, cows.

Close by on the ev­o­lu­tion­ary tree, this group is re­lat­ed to leeches found in In­dia and Tai­wan like Di­nob­della ferox, a ter­ri­ble leech no­to­ri­ous for feed­ing on mu­cus mem­branes and get­ting in­to var­i­ous hu­man ori­fices. All these spe­cies, and oth­ers from Mex­i­co, Af­ri­ca, and the Mid­dle East, make up the family Praob­del­l­i­dae, a group of leeches that seems to share this feed­ing be­hav­ior and which can threat­en hu­man health, sci­en­tists said.

The rela­t­ion­ship among leeches that cur­rently inhab­it dis­tant re­gions sug­gests that the com­mon an­ces­tor of this group must have lived when the con­ti­nents were pressed to­geth­er in­to a sin­gle land mass, called Pangaea, re­search­ers said.

“We named it Tyran­nob­della rex be­cause of its enor­mous teeth. Be­sides, the ear­li­est spe­cies in this family of these leeches no-doubt shared an en­vi­ron­ment with di­no­saurs about 200 mil­lion years ago,” Siddall said. “The new T. rex joins four oth­er spe­cies that use this ab­breviated name, in­clud­ing two Mi­o­cene fos­sils [a snail and a scar­ab beetle], a liv­ing Malaysian formi­cid ant, and, of course, the infa­mous Cre­ta­ceous the­ro­pod di­no­saur that was de­scribed in 1905 by an ear­li­er cu­ra­tor of the Amer­i­can Mu­se­um of Nat­u­ral His­to­ry.”


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The new T. rex has just one row of teeth, and they are huge for a leech—which is what this recently discovered animal is. Scientists have named the slimy critter Tyrannobdella rex, Latin for “tyrant leech king,” in homage to the similarly named dinosaur Tyrannosaurus rex (tyrant lizard king). The leech isn’t the only additional creature to have joined that famous reptile in receiving a moniker whose common abbreviation is T. rex. But it may well be the grossest. The bloodsucker was discovered three years ago in Perú when it was plucked from inside the nose of a girl who had taken a dip in a river, researchers said. They speculated that the leech might make a living by tormenting aquatic mammals in similar fashion. The 4.45 centimeter (almost 2 inch) animal has been now classified as a new species that lives in the remote parts of the Upper Amazon. The species, described in the research journal PLoS One, has led to revising the family tree of a group of leeches that has a habit of feeding from body orifices of mammals. “Because of our analysis of morphology [body form] and DNA, we think that Tyrannobdella rex is most closely related to another leech that gets into the mouths of livestock in Mexico,” said Anna Phillips, a graduate student affiliated with the American Museum of Natural History and an author of the paper. “We think the leech could feed on aquatic mammals, from their noses and mouths for example, where they could stay for weeks at a time.” Discoveries of new leech species are not uncommon. Although there are 600 to 700 species of described leeches, it is thought that there could be as many as10,000 species throughout the world in marine, land and fresh water environments. The analysis was conducted after the little T. rex was brought to the attention of Mark Siddall, curator in invertebrate zoology at the museum. He received a specimen collected by Renzo Arauco-Brown, a doctor from the Universidad Peruana Cayetano Heredia in Lima, Peru, who worked at a clinic in Chanchamayo province. Siddall said he immediately recognized it as a new species. His student Alejandro Oceguera-Figueroa described its weird form—a single jaw with eight very large teeth, and extremely small genitalia. Two earlier cases from 1997 were re-discovered from different clinics in the western Amazon, one from Lamas province and the other from Yochegua province. The leech was unique enough that it was not only classified as its own species, but its own genus, a larger evolutionary grouping that may include one more species. This analysis has led to a revision of the evolutionary relationships among several leech families, according to Phillips and colleagues. They describe the species as most closely related to Pintobdella chiapasensis, a leech from Chiapas that is typically hosted by tapir but also infests cows. Part of the research for this paper involved a Mexican expedition by Phillips and Oceguera-Figueroa to gather new specimens for genetic analysis. Close by on the evolutionary tree, this group is related to leeches found in India and Taiwan like Dinobdella ferox, a terrible leech notorious for feeding on mucus membranes and getting into various human orifices. All these species, and others from Mexico, Africa, and the Middle East, make up the family Praobdellidae, a group of leeches that seems to share this feeding behavior and which can threaten human health, scientists said. The relationship among leeches that currently inhabit distant regions suggests that the common ancestor of this group must have lived when the continents were pressed together into a single land mass, researchers said. “We named it Tyrannobdella rex because of its enormous teeth. Besides, the earliest species in this family of these leeches no-doubt shared an environment with dinosaurs about 200 million years ago when some ancestor of our T. rex may have been up that other T. rex’s nose,” said Siddall. “The new T. rex joins four other species that use this abbreviated name, including two Miocene fossils [a snail and a scarab beetle], a living Malaysian formicid ant, and, of course, the infamous Cretaceous theropod dinosaur that was described in 1905 by an earlier curator of the American Museum of Natural History.”