The dwarf freshwater stingray commonly known as the Black tailed antenna ray in the aquarium trade has finally been formally named in a recent issue of the journal Papéis Avulsos de Zoologia.
Marcelo Carvalho and Maíra Ragno name the new stingray from the upper and middle Amazon River drainage Plesiotrygon nana, after its small adult size (Latin nanus=dwarf).
Plesiotrygon nana differs from its only congener, P. iwamae, in a number of ways, including having the dorsal surface of the disc with highly convoluted yellowish lines or small spots composed into very fine rosettes or a combination of spots and irregular ocelli, a circular disc, a broadly rounded snout, very small and less rhomboidal spiracles, a short snout and a narrow mouth and nostrils.
In addition, the denticles on the dorsal surface of the tail are small, scattered, and not forming a row of enlarged spines, it has significantly fewer tooth rows in adult and preadult fish, fewer caudal vertebrae, and a higher number of pectoral radials.
This species also has a very small adult size, probably not surpassing 25cm/10" disc length or width.
For more information, see the paper: de Carvalho, MR and MP Ragno (2011) An unusual, dwarf new species of Neotropical freshwater stingray, Plesiotrygon nana sp. nov., from the upper and mid Amazon basin: the second species of Plesiotrygon (Chondrichthyes: Potamotrygonidae). Papéis Avulsos de Zoologia 51, pp. 101–138.