Nautilus (genus)

Genus of molluscs
the genus Nautilus

Nautilus is a marine cephalopod genus in the mollusk family Nautilidae. Species in this genus differ significantly, morphologically, from the two nautilus species in the adjacent sister taxon Allonautilus. The oldest fossils of the genus are known from the Late Eocene Hoko River Formation, in Washington State and from Late Eocene to Early Oligocene sediments in Kazakhstan. The oldest fossils of the modern species Nautilus pompilius are from Early Pleistocene sediments off the coast of Luzon in the Philippines. Various authors claim that the genus consists of between four and seven extant species; this remains the subject of debate. Nautiloids are typically found in shallow ocean waters in tropical seas, mainly within the Indo Pacific, from the Coral Triangle and Strait of Malacca to the open water South Pacific islands. In 1951, he determined that only extant species of Nautilus should be placed in the genus, despite many fossil species having already been assigned to it.

There has been much debate over the validity of species within the genus, and several identified species have since been reclassified or determined as taxonomic synonyms or nomen dubium (a doubtful classification). As of 2015, only four Nautilus species have been recognised, specifically N. pompilius, N. macromphalus, N. stenomphalus, and N. belauensis, For example, although N. pompilius was well studied in the 19th century, it was not until 1996 that soft tissues of Allonautilus scrobiculatus had been dissected. This same 2011 study, however, suggested that N. macromphalus was a species synonymous with A. scrobiculatus, leading to further debate over classification. These findings were also reinforced by the initial DNA studies conducted on the genus, which only revealed two phylogenetic species. A 2017 study determined that there were likely five Nautilus species, however these did not exactly correlate to the described species of the genus. It has been suggested that this organ contains chemoreceptors, in order to detect food or sample the surrounding water. Many shells recovered from areas of the world have not yet been identified down to the level of species, however, are still identifiable as members of the genus Nautilus. Shells have been found across a wide range of coastal areas, including Korea, Australia, Seychelles, Mauritius, the Philippines, Taiwan, Japan, Thailand, India, Sri Lanka, Kenya, and South Africa. An experiment with a Nautilus shell in an aquarium resulted in the shell floating for over two years, and one recovered shell was revealed to have been afloat for a period of 11 years. Several aquaria around the world host specimens of the genus, however, there have not yet been any successful attempts of breeding in captivity, despite viable eggs being produced at several locations.