60 



DANGEROUS MARINE ANIMALS 



Freshwater Stingrays - Potamotrygonidae 

 South American Freshwater Stingray, Potamotrygon motoro 

 (Miiller and Henle). (Fig. 31, Left). Found in the freshwater rivers 

 of Paraguay, and the Amazon River, south to Rio de Janeiro, 

 Brazil. An extremely dangerous species. 



Round Stingrays - Urolophidae 

 Round Stingray, Urolophus halleri (Cooper) (Fig. 31, Right). 

 Found from Point Conception, California, south to Panama Bay. 



GYMNURID 



MYLIOBATID 



DASYATID 



UROLOPHID 



Fig. 32. Anatomical types of venom organs that are found in the various 

 species of stingrays. (From Halstead and Bunker) 



Venom Apparatus of Stingrays. The venom apparatus, or sting, 

 of stingrays is an integral part of the caudal, or tail, appendage. A 

 study of stingrays reveals that there are four general anatomical 

 types of venom organs which vary somewhat in their effectiveness 

 as a defensive weapon. 



1. Gymnurid type (Fig. 32, Top). This type is found in the 

 butterfly rays (Gymnura). The sting is small, poorly developed, 

 and situated close to the base of a short tail, making it a relatively 

 feeble striking organ. 



