Brazilian scientists have described four new species during a revision of parasitic flukes found on freshwater stingrays.
Domingues and Marques of the University of Sao Paulo reviewed the monogenean fluke genus Potamotrygonocotyle and found that it contained a number of species specific to certain species of Potamotrygon ray.
Potamotrygonocotyle is the only known member of the family Monocotylidae which parasitises stingrays and was previously believed to hold a single species called P. tsalickisi.
However, the new study by Domingues and Marques which is due to be published shortly in the journal Systematic Parasitology, has revealed greater diversity in the genus than previously believed.
The authors wrote: "P. tsalickisi is redescribed and four new species are recognised and described based on samples collected from the gills of freshwater potamotrygonids from the La Plata river basin: Potamotrygonocotyle chisholmae n. sp. and P. dromedarius n. sp. from Potamotrygon motoro; Potamotrygonocotyle eurypotamoxenus n. sp. from Potamotrygon cf. motoro (type-host), P. castexi, P. falkneri and P. histrix; and Potamotrygonocotyle uruguayensis n. sp. from Potamotrygon brachyura.
"Potamotrygonocotyle is characterised by species possessing: slightly sinuous sclerotised ridges on all septa; two pairs of the dorsal haptoral accessory structures associated with the four posterior peripheral loculi and with anterior dorsal haptoral accessory structure bilobate or semicircular; and male copulatory organ without an accessory piece."
The Potamotrygonocotyle genus is not the only group of parasites that are specific to South America's Potamotrygon stingrays.
In 2005, a study of Potamotrygon motoro revealed a new species of cestode parasite found living in the fishes' spiral intestines. (See Motoro stingray study reveals new fish parasite).
For more information see the paper: Domingues MV, Marques FP (2007) - Revision of Potamotrygonocotyle Mayes, Brooks and Thorson, 1981 (Platyhelminthes: Monogenoidea: Monocotylidae), with descriptions of four new species from the gills of the freshwater stingrays Potamotrygon spp. (Rajiformes: Potamotrygonidae) from the La Plata river basin. Syst Parasitol. 2007 Jul;67(3):157-74.