The round rays (''Heliotrygon'') is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of freshwater stingrays in the family

Potamotrygonidae River stingrays or freshwater stingrays are Neotropical freshwater fishes of the family (biology), family Potamotrygonidae in the Order (biology), order Myliobatiformes, one of the four orders of Batoidea, batoids, cartilaginous fishes related to ...

. The genus is

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

to the

Amazon basin The Amazon basin is the part of South America drained by the Amazon River and its tributaries. The Amazon drainage basin covers an area of about , or about 35.5 percent of the South American continent. It is located in the countries of Bolivi ...

in South America. Despite being discovered decades earlier, the genus was only scientifically described in 2011.de Carvalho, M.R. and N.R. Lovejoy (2011). Morphology and phylogenetic relationships of a remarkable new genus and two new species of Neotropical freshwater stingrays from the Amazon basin (Chondrichthyes: Potamotrygonidae). Zootaxa 2776: 13-48. They mainly live in deep river channels, but approach the shore at night to feed on fish. Their discs are very circular in shape (including the snout), and they have tiny eyes and a relatively short tail with an essentially harmless,

vestigial Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...

stinger (sometimes even lacking). The largest confirmed disc width is , but there are reports of individuals where it was . Both species are greyish or brownish above, but while ''H. gomesi'' is overall plain without distinct markings, ''H. rosai'' has a white to creamy-white

vermiculated Vermiculation is a surface pattern of dense but irregular lines, so called from the Latin ''vermiculus'' meaning "little worm" because the shapes resemble worms, worm-casts, or worm tracks in mud or wet sand. The word may be used in a number of ...

pattern.

Species

* '' Heliotrygon gomesi'' M. R. de Carvalho &

Lovejoy ''Lovejoy'' is a British television comedy-drama mystery series, based on the novels by John Grant under the pen name Jonathan Gash. The show, which ran to 71 episodes over six series, was originally broadcast on BBC1 between 10 January 19 ...

, 2011 (Gomes's round ray) * '' Heliotrygon rosai'' M. R. de Carvalho &

, 2011 (Rosa's round ray)

References

Potamotrygonidae Freshwater fish of Brazil Freshwater fish of Peru Ray genera Freshwater fish genera {{Chondrichthyes-stub