Nautilus
| Nautilus | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
 Nautilus pompilius
| ||||||||||||||
| Scientific classification | ||||||||||||||
| ||||||||||||||
|
Allonautilus |
Nautilus (from Greek nautilos, 'sailor') is the common name of any marine creatures of the cephalopod family Nautilidae, the sole family of the suborder Nautilina. It comprises 6 very similar species in 2 genera, the type of which is the genus Nautilus. Though it more specifically refers to the species Nautilus pompilius, the name chambered nautilus is also used for any species of the Nautilidae.
Having survived relatively unchanged for millions of years, nautiluses represent the only living members of the subclass Nautiloidea, and are often considered to be "living fossils."
The name "Nautilus" originally referred to the Argonauta, otherwise known as paper nautiluses, because they allegedly use their two disk-bearing arms as sails (cf. Aristotle Historia Animalium 622b).
Description
The nautilus is similar in general form to other cephalopods, with a prominent head and tentacles. Nautiluses typically have more tentacles than other cephalopods, up to ninety. These tentacles are arranged into two circles and, unlike the tentacles of other cephalopods, they have no suckers, are undifferentiated and retractable. The radula is wide and distinctively has nine teeth. There are two pairs of gills.
Nautilus pompilius is the largest species in the genus. One form from western Australia may reach 268 mm in diameter. However, the majority of other nautiluses never exceed 20 cm. Nautilus macromphalus is the smallest species, usually measuring only 16 cm.
The shell
Nautiluses are the sole cephalopods whose bony structure of the body is externalized as a shell. The animal can withdraw completely into its shell, closing the opening with a leathery hood formed from two specially folded tentacles. The shell is coiled, calcareous, mother-of-pearl-lined and pressure resistant (imploding at a depth of about 800 m). The nautilus shell is composed of 2 layers: the outer layer is a matte white, while the inner layer is a striking white with iridescence. The innermost portion of the shell is pearlescent, blue-gray. The osmena pearl, contrarily to its name, is not a pearl, but a jewelry product derived from this part of the shell.
The shell is internally divided into chambers, the chambered section being called the phragmocone. The phragmocone is divided into camerae by septa, all of which are pierced in the middle by a duct, the siphuncle. As the nautilus matures its body moves forward, sealing the camerae behind it with a new septum. The last fully open chamber, also the largest one, is used as the living chamber. The number of camerae increases from around four at the moment of hatching to thirty or more in adults.
The shell coloration also keeps the animal cryptic in the water. When seen from the top, the shell is darker in color and marked with irregular stripes, which makes it blend into the darkness of the water below. On the contrary, the underside is almost completely white, making the animal indistinguishable from brighter waters near the ocean surface. This mode of camouflage is named countershading.
The nautilus shell presents one of the finest natural examples of a logarithmic spiral. (It is sometimes incorrectly claimed to be a golden spiral as well.)
A nautilus shell when viewed from above
The same shell viewed from underneath
Hemishell showing the camerae in a logarithmic spiral
Buoyancy and movement
In order to swim, the nautilus draws water into and out of the living chamber with the hyponome, which makes use of jet propulsion. When water is inside the chamber, the siphuncle extracts salt from it and diffuses it into the blood. When water is pumped out, the animal adjusts its buoyancy with the gas contained in the chamber. Buoyancy can be controlled by the osmotical pumping of gas and fluid into or from the camerae along the siphuncles. The control of buoyancy in this manner limits the nautilus; they cannot operate under extreme hydrostatic pressures.
The animal can also crawl on land or on the seabed.
In the wild, nautiluses usually inhabit depths of about 300 m, rising to around 100 m at night for feeding, mating and egg laying. The shell of the nautilus cannot withstand depths greater than approximately 800 m.
Diet and sensory system
Nautiluses are predators and feed mainly on shrimp, small fish and crustaceans, which are captured by the tentacles. However, due to the very little energy they devote to swimming, they need only eat once a month. Unlike other cephalopods, they do not have good vision; their eye structure is highly developed but lacks a solid lens. They have a simple "pinhole" lens through which water can pass. Instead of vision, the animal is thought to use olfaction as the primary sensory means during foraging, locating or identifying potential mates.
Reproduction and lifespan
Nautiluses are sexually dimorphic and reproduce by laying eggs. Attached to rocks in shallow waters, the eggs take twelve months to develop before hatching out at around 30 mm long. Females spawn once per year and regenerate their gonads, making nautiluses the only cephalopods to present iteroparity or polycyclic spawning. The lifespan of nautiluses is about 20 years, which is exceptionally long for a cephalopod.
Classification
The genus Nautilus contains six extant species and several extinct species.
- Genus Allonautilus
- Allonautilus perforatus
- Allonautilus scrobiculatus
- Genus Nautilus
- Nautilus belauensis
- †Nautilus clarkanus
- †Nautilus cookanum
- Nautilus macromphalus
- Nautilus pompilius (type)
- Nautilus pompilius pompilius
- Nautilus pompilius suluensis
- †Nautilus praepompilius
- Nautilus stenomphalus
Dubious or uncertain taxa
| Binomial name and author citation | Current systematic status | Type locality | Type repository |
|---|---|---|---|
| Nautilus alumnus Iredale, 1944 | Species dubium [fide Saunders (1987:49)] | Queensland, Australia | Not designated [fide Saunders (1987:49)] |
| Nautilus ambiguus Sowerby, 1848 | Species dubium [fide Saunders (1987:48)] | Not designated | Unresolved |
| Nautilus beccarii Linne, 1758 | Non-cephalopod; Foraminifera [fide Frizzell and Keen (1949:106)] | ||
| Nautilus calcar Linne, 1758 | ?Non-cephalopod; Foraminifera Lenticulina | Adriatic Sea | Unresolved; Linnean Society of London? |
| Nautilus crispus Linne, 1758 | Undetermined | Mediterranean Sea | Unresolved; Linnean Society of London? |
| Nautilus crista Linne, 1758 | Non-cephalopod; Turbo [fide Dodge (1953:14)] | ||
| Nautilus fascia Linne, 1758 | Undetermined | Adriatic Sea | Unresolved; Linnean Society of London? |
| Nautilus granum Linne, 1758 | Undetermined | Mediterranean Sea | Unresolved; Linnean Society of London? |
| Nautilus lacustris Lightfoot, 1786 | Non-cephalopod; Helix [fide Dillwyn (1817:339)] | ||
| Nautilus legumen Linne, 1758 | Undetermined | Adriatic Sea | Unresolved; Linnean Society of London? |
| Nautilus micrombilicatus Joubin, 1888 | Nomen nudum | ||
| Nautilus obliquus Linne, 1758 | Undetermined | Adriatic Sea | Unresolved; Linnean Society of London? |
| Nautilus pompilius marginalis Willey, 1896 | Species dubium [fide Saunders (1987:50)] | New Guinea | Unresolved |
| Nautilus pompilius moretoni Willey, 1896 | Species dubium [fide Saunders (1987:49)] | New Guinea | Unresolved |
| Nautilus pompilius perforatus Willey, 1896 | Species dubium [fide Saunders (1987:49)] | New Guinea | Unresolved |
| Nautilus radicula Linne, 1758 | ?Non-cephalopod; Foraminifera Nodosaria | Adriatic Sea | Unresolved; Linnean Society of London? |
| Nautilus raphanistrum Linne, 1758 | Undetermined | Mediterranean Sea | Unresolved; Linnean Society of London? |
| Nautilus raphanus Linne, 1758 | Undetermined | Adriatic Sea | Unresolved; Linnean Society of London? |
| Nautilus semi-lituus Linne, 1758 | Undetermined | Liburni, Adriatic Sea | Unresolved; Linnean Society of London? |
| Nautilus sipunculus Linne, 1758 | Undetermined | "freto Siculo" | Unresolved; Linnean Society of London? |
| Nautilus texturatus Gould, 1857 | Nomen nudum | ||
| Octopodia nautilus Schneider, 1784 | Rejected specific name [fide Opinion 233, ICZN (1954:278)] |
Distribution
Nautiluses are only found in the Indo-Pacific, from 30° N to 30° S latitude and 90° to 185° W longitude. They inhabit the deep slopes of coral reefs.
Natural history
Fossil records indicate that nautiluses have not evolved much during the last 500 million years, and nautiloids were much more extensive and varied 200 million years ago. Many were initially straight-shelled, as in the extinct genus Lituites. They developed in the Cambrian period and became a significant sea predator in the Ordovician period. Certain species reached over 2.5 meters in size. The other cephalopod subclass, Coleoidea, diverged from the Nautilidae long ago and the nautilus has remained relatively unchanged since. Extinct relatives of the nautilus include ammonites, such as the baculites and goniatites.
See also
- Coelacanth - another living fossil
- The Chambered Nautilus, a poem of Oliver Wendell Holmes
ReferencesISBN links support NWE through referral fees
- Sweeney, M.J. 2002. Taxa Associated with the Family Nautilidae Blainville, 1825. Tree of Life web project.
- Ward, P.D. 1988. In Search of Nautilus. Simon and Schuster.
External links
Template:CephBase Family
- Nautilidae discussion forum at TONMO.com
- Waikïkï Aquarium: Marine Life Profile: Chambered Nautilus
- A molecular and karyological approach to the taxonomy of Nautilus
Credits
New World Encyclopedia writers and editors rewrote and completed the Wikipedia article in accordance with New World Encyclopedia standards. This article abides by terms of the Creative Commons CC-by-sa 3.0 License (CC-by-sa), which may be used and disseminated with proper attribution. Credit is due under the terms of this license that can reference both the New World Encyclopedia contributors and the selfless volunteer contributors of the Wikimedia Foundation. To cite this article click here for a list of acceptable citing formats.The history of earlier contributions by wikipedians is accessible to researchers here:
The history of this article since it was imported to New World Encyclopedia:
Note: Some restrictions may apply to use of individual images which are separately licensed.
