 The viper dogfish has a slender , cylindrical body and a moderately flattened head with a very short and blunt snout . Behind the large oval eyes are narrow , elliptical spiracles . The nostrils are nearly vertical slits . The jaws are long and narrowly triangular , and can be protruded from the head . The teeth are distinctively fang @-@ like and widely spaced ; the most anterior teeth are grooved lengthwise . Six to 10 upper and seven to 10 lower tooth rows occur on each side , along with a single tooth row at the upper and lower symphyses ( jaw midpoints ) . The teeth are largest at the symphysis and decline in size towards the corners of the mouth . When the mouth is closed , the upper symphysial tooth overlaps the lower , while the lateral teeth interlock . Five gill slits are seen , with the fifth pair longer than the others . 
