 The porcupine ray ( Urogymnus asperrimus ) is a rare species of stingray in the family Dasyatidae and the only member of its genus . This bottom @-@ dweller is found throughout the tropical Indo @-@ Pacific , as well as off West Africa . It favors sand , coral rubble , and seagrass habitats in inshore waters to a depth of 30 m ( 100 ft ) . A large and heavy @-@ bodied species reaching 1 @.@ 2 – 1 @.@ 5 m ( 3 @.@ 9 – 4 @.@ 9 ft ) in width , the porcupine ray has a nearly circular , plain @-@ colored pectoral fin disc and a thin tail without any fin folds . Uniquely within its family , it lacks a venomous stinging spine . However , an adult ray can still defend itself ably with the many large , sharp thorns found over its disc and tail . 
