Nautilus stenomphalus, also known as the White-patch Nautilus, is a species of nautilus

Nautilus

Nautilus is the common name of marine creatures of cephalopod family Nautilidae, the sole extant family of the superfamily Nautilaceae and of its smaller but near equal suborder, Nautilina. It comprises six living species in two genera, the type of which is the genus Nautilus...

 native to the Great Barrier Reef

Great Barrier Reef

The Great Barrier Reef is the world'slargest reef system composed of over 2,900 individual reefs and 900 islands stretching for over 2,600 kilometres over an area of approximately...

. N. stenomphalus is very similar to N. pompilius

Chambered Nautilus

The Chambered Nautilus, Nautilus pompilius, is the best-known species of nautilus. The shell, when cut away reveals a lining of lustrous nacre and displays a nearly perfect equiangular spiral, although it is not a golden spiral. The shell exhibits countershading, being light on the bottom and dark...

and may in fact represent a subspecies. It is separated by the absence of a thickened callus

Callus (disambiguation)

Callus means a hardening of a certain object or substance. It can refer to:*Callus, an area of toughened skin*Fibrocartilage callus, the temporary new bony tissue that forms at the ends of a fractured bone...

 and the presence of white patches in the umbilical and shoulder regions of the shell. The sheaths of this species have scalloped edges compared with the smooth sheaths of N. pompilius. N. stenomphalus also differs slightly in hood ornamentation. The shell is usually up to around 180 mm in diameter, although the largest specimen ever recorded measured 201 mm.