Stingrays (ie, elasmobranchs) are bottom-dwelling cartilaginous fish that have a flattened body, one or more stout spines on the tail, gill slits on the lower surface of the head, teeth modified into 2 large crushing plates, and no dorsal fin. They are not aggressive toward humans; however, injuries from these animals are very common. Stingrays are shown in the images below.
Stingrays from the northern hemisphere make up the family Dasyatidae. These fish are marine creatures (ie, live in salt water) but also have been found in brackish waters and bays. Another ray family (Potamotrygonidae)
contains poisonous species known as freshwater stingrays. These freshwater stingrays live in lakes and rivers of South America.
See Deadly Sea Envenomations, a Critical Images slideshow, to help make an accurate diagnosis.