 The tail is moderately thick and measures about 0 @.@ 5 – 0 @.@ 7 times as long as the disc . One or two serrated stinging spines are present on its dorsal surface , well back from the base . The end of the tail bears a long , low leaf @-@ shaped caudal fin that is nearly symmetrical above and below . The skin is delicate and entirely lacking dermal denticles . The disc is purplish to pinkish brown above , darkening slightly at the fin margins ; the skin is easily abraded , leaving white patches . The underside of the disc is white with dark margins on the pectoral and pelvic fins . The snout is translucent , and the tail and caudal fin are almost black . The largest known specimen is a female 1 @.@ 7 m ( 5 @.@ 6 ft ) long . 
