Potamotrygonidae
Peacock stingrays ( Potamotrygon motoro )
The freshwater stingrays ( Potamotrygonidae ) in South America are the only family of cartilaginous fish ( Chondrichtyes ) that is found exclusively in fresh water. Among them are four genera with about 25 species.
The Potamotrygonidae are probably monophyletic and descendants of Stingray, who lived at the mouth of the Uramazonas when he was still flowing into the Pacific. Through the unfolding of the Andes, they were cut off from their former habitat. The family probably developed at the end of the Cretaceous or early Tertiary. From the Eocene the Potamotrygonidae are in the fossil record. They show by reducing the Rektaldrüse and low urea content in the blood of their adaptation to the freshwater.
Features
Freshwater stingrays are often circular, the genus Paratrygon slightly longer than broad. You have no dorsal fins and no tail fin. The tail is whip-like, with a venomous, barbed stinger. All 6 to 12 months, a new spike grows.
Their color is usually brown, gray or black with a drawing of colored dots, spots or squiggles. You can reach depending on a diameter of 25 inches to just over one meter.
Reproduction
Like most rays are the freshwater stingrays viviparous ( ovoviviparous ). They have internal fertilization. Most are between two and seven, rare to twelve juveniles born who can still have remnants of the yolk sac.
Dissemination
Freshwater stingrays are native only to the tropical areas of South America. However, they live only in rivers that flow into the Atlantic Ocean or the Caribbean, but not in the basin of the Rio São Francisco. Most species live only in a river system, some endemic only in a certain flow (eg Potamotrygon leopoldi ). Only a few species, such as Potamotrygon Potamotrygon motoro and orbignyi, have another distribution area, which includes several river systems.
Genera
There are four genera, the genus containing about 25 species Potamotrygon and three others, to which only two or one kind belong.
- Genus Heliotrygon Carvalho & Lovejoy, 2011 Heliotrygon gomesi De Carvalho & Lovejoy, 2011
- Heliotrygon Rosai De Carvalho & Lovejoy, 2011
- Paratrygon aiereba ( Müller & Henle, 1841)
- Plesiotrygon iwamae Rosa, Castello & Thorson, 1987
- Plesiotrygon nana de Carvalho & Ragno, 2011
In addition to these three, living in freshwater species, are considered by some scientists schmardae also usually counted among the stingrays ( Dasyatidae ) marine species of the genus Taeniura and Himantura pacifica and Himantura counted among the Potamotrygonidae.