Nautilus is a genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of cephalopod

Cephalopod

A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...

s in the family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 Nautilidae

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...

. Species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 in this genus differ significantly in terms of morphology

Morphology (biology)

In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....

 from those placed in the sister taxon

Taxon

|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...

 Allonautilus

Allonautilus

The genus Allonautilus contains two species of nautiluses, which differ significantly in terms of morphology from those placed in the sister taxon Nautilus. Allonautilus is now thought to be a descendant of Nautilus and the latter paraphyletic.-External links:*...

. The oldest fossils of the genus are known from the Late Eocene Hoko River Formation

Hoko River Formation

The Hoko River Formation is a Late Eocene marine sedimentary geologic formation. The formation is exposed in outcrops along the Strait of Juan de Fuca on the Olympic Peninsula in Washington State, USA. It is known for containing numerous fossils of crabs...

, in Washington State and from Late-Eocene to Early Oligocene sediments in Kazakhstan

Kazakhstan

Kazakhstan , officially the Republic of Kazakhstan, is a transcontinental country in Central Asia and Eastern Europe. Ranked as the ninth largest country in the world, it is also the world's largest landlocked country; its territory of is greater than Western Europe...

. The oldest fossils of the modern species Nautilus pompilius are from Early Pleistocene sediments off the coast of Luzon

Luzon

Luzon is the largest island in the Philippines. It is located in the northernmost region of the archipelago, and is also the name for one of the three primary island groups in the country centered on the Island of Luzon...

 in the Philippines

Philippines

The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...

.

The common term 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...

usually refers to any extant members of the Nautilidae family.

Species

• Nautilus belauensis
  Palau Nautilus
  Nautilus belauensis, also known as the Palau Nautilus, is a species of nautilus native to the waters around the Pacific island nation of Palau. N. belauensis is very similar to Nautilus pompilius and shares with this species a closed umbilicus covered with a callus...
  
  
• †Nautilus cookanum
  Nautilus cookanum
  Nautilus cookanum is an extinct species of nautilus. It lived during the Eocene epoch. N. cookanum has been grouped into a single taxon together with extant species based on their shared shell characters. Fossils of the species from the Late Eocene Hoko River Formation are noted as one of the two...
  
  
• Nautilus macromphalus
  Bellybutton Nautilus
  The Bellybutton Nautilus is a species of nautilus native to the waters off New Caledonia, the Loyalty Islands, and northeastern Australia. The shell of this species lacks a callus, leaving the umbilicus exposed, in which the inner coils of the shell are visible...
  
  
• Nautilus pompilius (type
  Type species
  In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
  
  )
  • Nautilus pompilius pompilius
  • Nautilus pompilius suluensis
• †Nautilus praepompilius
  Nautilus praepompilius
  Nautilus praepompilius is an extinct species of nautilus. It lived during the Late Eocene through Oligocene epochs. Fossil specimens have been uncovered from the Chegan Formation of Kazakhstan. N. praepompilius has been grouped into a single taxon together with extant species based on their shared...
  
  
• Nautilus stenomphalus
  White-patch Nautilus
  Nautilus stenomphalus, also known as the White-patch Nautilus, is a species of nautilus native to the Great Barrier Reef. N. stenomphalus is very similar to N. pompilius and may in fact represent a subspecies. It is separated by the absence of a thickened callus and the presence of white patches in...