(Rhizoprionodon acutus)
The largest member of its genus,off West Africa the milk shark has been reported to reach 1.78 m (5.8 ft) and 22 kg (49 lb) for males,and 1.65 m (5.4 ft) and 17 kg (37 lb) for females,though there is uncertainty regarding the species identity of these specimens.Even if accepted,these figures are considered exceptional and most individuals do not exceed 1.1 m (3.6 ft) in length.Generally,females are heavier and attain a greater maximum size than males.The milk shark has a slender build with a long,pointed snout,large,round eyes with nictitating membranes (protective third eyelids),and no spiracles.On each side of the head behind the corner of the jaw,there are usually seven to 15 enlarged pores.The nostrils are small,as are the adjacent triangular skin flaps.There are long furrows at the corners of the mouth on both the upper and lower jaws.The tooth rows number 24–25 in both jaws.The upper teeth are finely serrated and strongly oblique;the lower teeth have a similar shape,though the serrations are smaller and the tips curve gently upward.The teeth of juveniles are smooth-edged.The broad,triangular pectoral fins originate below the third or fourth gill slits,and are no longer than the front margin of the first dorsal fin.The anal fin is about twice as long as the second dorsal fin and preceded by long ridges.The first dorsal fin originates over the pectoral fin free rear tips,and the much smaller second dorsal fin originates over the last third of the anal fin base.The dorsal fins do not have a ridge between them.The lower lobe of the caudal fin is well-developed and the upper lobe has a ventral notch near the tip.This shark is plain gray,brown-gray,or purple-gray above,and white below.The leading edge of the first dorsal fin and the trailing edge of the caudal fin may be dark,and the trailing edges of the pectoral fins may be light.