The medium length beak distinct is distinct from the bulbous forehead in both sexes, though adult males have a larger head with a more pronounced melon. As males mature the large forehead surface becomes flattened like the end of a barrel and overhangs the beak. The mouthline is weakly sinusoidal.
Two main types of dorsal body pigmentation exist in adults. Most common dorsal coloration in adult H. planifrons is brownish to yellowish, though bluish gray or bluish black color morphs exist. Head and ventral regions may be paler. In juveniles the light nuchal band can either be prominent or muted, and may fade with age. Eye patches may be pronounced or almost absent. The dorsal aspect of the flippers may be whitish or dark.
Length of adult animals ranges between 6 - 8 m. Recorded maximum body length for adult male and female individuals is 6.9 m and 7.5 m, respectively. Mean body length at birth is unknown.
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