Sawfish
Sawfish are primarily found in coastal marine and estuarine brackish waters, but they are euryhaline (can adapt to various salinities) and also found in freshwater. The largetooth sawfish, alternatively called the freshwater sawfish, has the greatest affinity for freshwater. For example, it has been reported as far as up the Amazon River and in Lake Nicaragua, and its young spend the first years of their life in freshwater. In contrast, the smalltooth, green and dwarf sawfish typically avoid pure freshwater, but may occasionally move far up rivers, especially during periods when there is an increased salinity. There are reports of narrow sawfish seen far upriver, but these need confirmation and may involve misidentifications of other species of sawfish.
Squalomorphii
The order Pristiophoriformes is a small order of unique sharks called sawsharks. Sawsharks have a long snout covered in teeth, between 5-6 gill slits, and no anal fin. They also have a pair of barbels usually located halfway down the snout. Sawsharks are frequently confused with sawfish, which are members of the ray order Pristiformes. Sawsharks can be discerned from sawfish thanks to their lateral gill slits, which differ from the sawfish's ventral gill slits. These sharks can mostly be found in deep benthic environments. Fossils of members of this order have been found since the late Jurassic period.