Like all Nautilus species, N. macromphalus usually lives at depths of several hundred metres.
The tentacles of this species are long and thin, having raised ridges which help provide grip when catching prey.
The shell is usually up to around 16 cm in diameter, although the largest specimen ever recorded measured 180 mm.
[2] More than 35 shells of N. macromphalus dating to around 6400–7100 years BP were found in a cenote on Lifou, the Loyalty Islands.
Based on these radiocarbon dates it is thought the cenote was connected to marine waters for some 700 years before becoming cut off completely.