Nautilus belauensis, also known as the Palau 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 waters around the Pacific

Pacific Ocean

The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

 island nation

Island nation

An island country is a state whose primary territory consists of one or more islands or parts of islands. As of 2011, 47 of the 193 UN member states are island countries.-Politics:...

 of Palau

Palau

Palau , officially the Republic of Palau , is an island nation in the Pacific Ocean, east of the Philippines and south of Tokyo. In 1978, after three decades as being part of the United Nations trusteeship, Palau chose independence instead of becoming part of the Federated States of Micronesia, a...

. N. belauensis is very similar to Nautilus 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 shares with this species a closed umbilicus covered with a 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...

. It differs on the basis of a modified radula

Radula

The radula is an anatomical structure that is used by molluscs for feeding, sometimes compared rather inaccurately to a tongue. It is a minutely toothed, chitinous ribbon, which is typically used for scraping or cutting food before the food enters the esophagus...

 and fine raised ridges across and along the shell, which form a cross-grid texture. N. belauensis is the second largest nautilus

Cephalopod size

Size has been one of the most interesting aspects of cephalopod science to the general public. This article lists the largest cephalopods from various groups, sorted in order of mantle length, total length, weight, and shell diameter...

 after the giant form of N. pompilius 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...

. The shell is usually up to around 210 mm in diameter, although specimens up to 226 mm have been recorded.