Yes, these guys are flat. Not only are they flat, but they are also very lazy. No, they don't do much compared to your typical Potamotrygon sp you see all the time. They are more of an ambush predator. And, yes, they do get huge. And I do mean huge. Like over 4 week in diameter sometime for some species. They pop up sometime in aquarium trade under such names as “apple ray”, “china ray”, “coolie ray” or “eyebrow ceja ray”. But not a lot of people keep them due to their size and to the fact that they are somewhat difficult to keep. They are difficult to wean onto frozen foods and they can not be mixed with large eyed Potamotrygon species because they will either starve or be bullied to death.
These guys are your typical ambush predators, despite their small eyes. They are also known as “eyebrow ceja ray”, “manzana ray” or “apple ray”. I guess, they do look like apples somewhat. They reach about 130cm in diameter and can way up to 60 kg (that's over 130 pounds if you are behind on SI system). There is only one specie in Paratrygon genus. These stingrays are found in Brazil, Peru, and Colombia.
This has a broken tail. It should be much longer
These photos are kind of sad, but you can see how huge they get
These guys are the coolest small eyed rays in my opinion. For the longest time Heliotrygon gomesi did not have a proper scientific name. They were simply called “china ray”, I guess because they look like china plates. They live in Brazil, in the upper Rio Amazonas basin according to the material studied, but suspected to enter the lower reaches of most major tributaries and the lower Rio Amazon basin as well. They were actually in the news a few years ago under a false headline “new ray discovered”. In reality they were discovered a long time ago and were even imported in US and Europe. The news simply misreported a scientific paper where they finally got an official Latin name
These are also newly described. Before getting a scientific name, they were known as “coolie ray” They are slightly smaller, and max out at 80cm (which is still a pretty huge size). It looks pretty similar to the China Ray, but Heliotrygon rosai has white verniculate markings all over its disc.