Nautilus

For other uses, see Nautilus (disambiguation).

Nautilus Temporal range: Triassic–Present[1] PreЄ Є O S D C P T J K Pg N
Nautilus belauensis
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Cephalopoda
Subclass:	Nautiloidea
Order:	Nautilida
Superfamily:	Nautilaceae
Family:	Nautilidae Blainville, 1825
Genera
†Carinonautilus †Cenoceras †Eutrephoceras †Pseudocenoceras †Strionautilus Allonautilus Nautilus

Nautilus (from Greek ναυτίλος, 'sailor') 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. Though it more specifically refers to species Nautilus pompilius, the name chambered nautilus is also used for any species of the Nautilidae.

Nautilidae, both extant and extinct, are characterized by involute or slightly evolute shells that are generally smooth, with compressed or depressed whorl sections, straight to sinuous sutures, and a tubular, generally central siphuncle.^[2] Having survived relatively unchanged for millions of years, nautiluses represent the only living members of the subclass Nautiloidea, and are often considered "living fossils."

The name "Nautilus" originally referred to the Argonauta, otherwise known as paper nautiluses, because the ancients believed these animals used their two expanded arms as sails (cf. Aristotle Historia Animalium 622b). However, this octopus is not closely related to the Nautiloidea.

Anatomy

The anatomy of Nautilus. The top figure is dissected; the bottom just has the shell removed.

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. These are the only remnants of the ancestral metamerism to be visible in extant cephalopods.^[3]:56

Nautilus pompilius is the largest species in the genus. One form from western Australia may reach 26.8 centimetres (10.6 in) in diameter. However, most other nautilus species never exceed 20 centimetres (7.9 in). Nautilus macromphalus is the smallest species, usually measuring only 16 centimetres (6.3 in).

Shell

Nautilus hemishell showing the camerae in a logarithmic spiral

A nautilus shell viewed from above (left), and from underneath (right)

Nautiluses are the sole living cephalopods whose bony body structure is externalized as a shell. The animal can withdraw completely into its shell and close the opening with a leathery hood formed from two specially folded tentacles. The shell is coiled, aragonitic,^[4] nacreous and pressure resistant, imploding at a depth of about 800 metres (2,600 ft). The nautilus shell is composed of 2 layers: a matte white outer layer, and a striking white iridescent inner layer. The innermost portion of the shell is a pearlescent blue-gray. The osmena pearl, contrarily to its name, is not a pearl, but a jewellery product derived from this part of the shell.

Internally, the shell divides into camerae (chambers), the chambered section being called the phragmocone. The divisions are defined by septa, each of which is pierced in the middle by a duct, the siphuncle. As the nautilus matures it creates new, larger camerae, and moves its growing body into the larger space, sealing the vacated chamber with a new septum. The camerae increase in number from around four at the moment of hatching to thirty or more in adults.

The shell colouration also keeps the animal cryptic in the water. When seen from above, the shell is darker in color and marked with irregular stripes, which helps it blend into the dark water below. The underside is almost completely white, making the animal indistinguishable from brighter waters near the surface. This mode of camouflage is named countershading.

The nautilus shell presents one of the finest natural examples of a logarithmic spiral, although it is not a golden spiral. The use of nautilus shells in art and literature is covered at nautilus shell.

Tentacles

Nautilus tentacles differ from those of other cephalopods. Lacking pads, the tentacles stick to prey by virtue of their ridged surface.^[5] Nautiloids have a powerful grip. Attempts to take an object already seized by a nautilus may tear tentacles away from the creature, which remain firmly attached to the surface of the object.^[5] Two pairs of tentacles are separate from the other 90-ish, the pre-ocular and post-ocular, situated before and behind the eye. These are more evidently grooved, with more pronounced ridges. They are extensively ciliated and serve an olfactory purpose.^[5][6][7]

Physiology

Buoyancy and movement

Nautilus locomotion
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Nautilus with extended tentacles and hyponome visible

To swim, the nautilus draws water into and out of the living chamber with its hyponome, which uses jet propulsion. While water is inside the chamber, the siphuncle extracts salt from it and diffuses it into the blood. The animal adjusts its buoyancy by osmotically pumping gas and fluid into or out of the camerae along the siphuncles. This limits them; they cannot operate under the extreme hydrostatic pressures found at depths greater than approximately 800 metres (2,600 ft).

In the wild, nautiluses usually inhabit depths of about 300 metres (980 ft), rising to around 100 metres (330 ft) at night to feed, mate and to lay eggs.

Senses

Head of Nautilus pompilius showing the eye

Unlike many other cephalopods, they do not have good vision; their eye structure is highly developed but lacks a solid lens. They have a simple "pinhole" eye open to the environment.

Instead of vision, the animal is thought to use olfaction as the primary sense for foraging, locating or identifying potential mates.^[8]

Reproduction and lifespan

Nautiluses reproduce by laying eggs. Gravid females attach the fertilized eggs to rocks in shallow waters, whereupon the eggs take eight to twelve months to develop until the 30 millimetres (1.2 in) juveniles hatch. Females spawn once per year and regenerate their gonads, making nautiluses the only cephalopods to present iteroparity or polycyclic spawning.

Nautiluses are sexually dimorphic, in that males have four tentacles modified into an organ, called the "spadix," which transfers sperm into the female's mantle during mating.

The lifespan of nautiluses may exceed 20 years, which is exceptionally lengthy for a cephalopod.^[9] However, nautiluses typically reach sexual maturity when they are about 15 years old.^[10]

Ecology

Diet

Nautiluses are predators that feed mainly on small fish, shrimp, and other crustaceans, which are captured by the tentacles. Due to the limited energy they expend in swimming, nautiloids only need to eat once a month.

Range, habitat, and status

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. There is growing concern that nautiluses are being greatly overfished.^[11] Their limited ecological range and the late onset of their sexual maturity combined with this overfishing has led to recent investigations into the need to protect them from possible endangerment or extinction.^[12]

Evolution

Shell characters of the genera Allonautilus and Nautilus

Fossil records indicate that nautiluses have not evolved much during the last 500 million years. 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 metres (8 ft 2 in) in size. The other cephalopod subclass, Coleoidea, diverged from the Nautilidae long ago and the nautilus has remained relatively unchanged since. Nautiloids were much more extensive and varied 200 million years ago. Extinct relatives of the nautilus include ammonites, such as the baculites and goniatites.

The Nautilidae has its origin in the Trigonocerataceae (Centroceratina), specifically in the Syringonautilidae of the Late Triassic^[2] and continues to this day with Nautilus, the type genus, and its close relative, Allonautilus.

Fossil genera

The Nautilidae begin with Cenoceras in the Late Triassic, a highly varied genus that makes up the Jurassic Cenoceras complex. Cenoceras is evolute to involute, and globular to lentincular; with a suture that generally has a shallow ventral and lateral lobe and a siphuncle that is variable in position but never extremely ventral or dorsal. Cenoceras is not found above the Middle Jurassic and is followed by the Upper Jurassic-Miocene Eutrephoceras.

Eutrephoceras is generally subgobular, broadly rounded laterally and ventrally, with a small to occluded umbilicus, broadly rounded hyponomic sinus, only slightly sinuous sutures, and a small siphuncle that is variable in position.

Next to appear is the Lower Cretaceous Strionautilus from India and the European ex-USSR, named by Shimankiy in 1951. Strionautilus is compressed, involute, with fine longitudinal striations. Whorl sections are subrectangular, sutures sinuous, the siphuncle subcentral.

Also from the Cretaceous is Pseudocenoceras, named by Spath in 1927. Pseudocenoceras is compressed, smooth, with subrectangular whorl sections, flattened venter, and a deep umbilicus. The suture crosses the venter essentially straight and has a broad, shallow, lateral lobe. The siphuncle is small and subcentral. Pseudocenoceras is found in the Crimea and in Libya.

Carinonautilus is a genus from the Upper Cretaceous of India, named by Spengler in 1919. Carinonautilus is a very involute form with high whorl section and flanks that converge on a narrow venter that bears a prominent rounded keel. The umbilicus is small and shallow, the suture only slightly sinuous. The siphuncle is unknown.

Taxonomy

Nautilus shells: N. macromphalus (left), A. scrobiculatus (centre), N. pompilius (right)

The family Nautilidae contains six extant species and several extinct species.

• Genus Allonautilus
  • A. perforatus
  • A. scrobiculatus
• Genus Nautilus
  • N. belauensis
  • †N. cookanum
  • N. macromphalus
  • N. pompilius (type)
    • N. p. pompilius
    • N. p. suluensis
  • †N. praepompilius
  • N. stenomphalus

Dubious or uncertain taxa

The following taxa associated with the family Nautilidae are of uncertain taxonomic status:^[13]

Binomial name and author citation	Current systematic status	Type locality	Type repository
N. alumnus Iredale, 1944	Species dubium [fide Saunders (1987:49)]	Queensland, Australia	Not designated [fide Saunders (1987:49)]
N. ambiguus Sowerby, 1848	Species dubium [fide Saunders (1987:48)]	Not designated	Unresolved
N. beccarii Linne, 1758	Non-cephalopod; Foraminifera [fide Frizzell and Keen (1949:106)]
N. calcar Linne, 1758	?Non-cephalopod; Foraminifera Lenticulina	Adriatic Sea	Unresolved; Linnean Society of London?
N. crispus Linne, 1758	Undetermined	Mediterranean Sea	Unresolved; Linnean Society of London?
N. crista Linne, 1758	Non-cephalopod; Turbo [fide Dodge (1953:14)]
N. fascia Linne, 1758	Undetermined	Adriatic Sea	Unresolved; Linnean Society of London?
N. granum Linne, 1758	Undetermined	Mediterranean Sea	Unresolved; Linnean Society of London?
N. lacustris Lightfoot, 1786	Non-cephalopod; Helix [fide Dillwyn (1817:339)]
N. legumen Linne, 1758	Undetermined	Adriatic Sea	Unresolved; Linnean Society of London?
N. micrombilicatus Joubin, 1888	Nomen nudum
N. obliquus Linne, 1758	Undetermined	Adriatic Sea	Unresolved; Linnean Society of London?
N. pompilius marginalis Willey, 1896	Species dubium [fide Saunders (1987:50)]	New Guinea	Unresolved
N. pompilius moretoni Willey, 1896	Species dubium [fide Saunders (1987:49)]	New Guinea	Unresolved
N. pompilius perforatus Willey, 1896	Species dubium [fide Saunders (1987:49)]	New Guinea	Unresolved
N. radicula Linne, 1758	?Non-cephalopod; Foraminifera Nodosaria	Adriatic Sea	Unresolved; Linnean Society of London?
N. raphanistrum Linne, 1758	Undetermined	Mediterranean Sea	Unresolved; Linnean Society of London?
N. raphanus Linne, 1758	Undetermined	Adriatic Sea	Unresolved; Linnean Society of London?
N. semi-lituus Linne, 1758	Undetermined	Liburni, Adriatic Sea	Unresolved; Linnean Society of London?
N. sipunculus Linne, 1758	Undetermined	"freto Siculo"	Unresolved; Linnean Society of London?
N. texturatus Gould, 1857	Nomen nudum
Octopodia nautilus Schneider, 1784	Rejected specific name [fide Opinion 233, ICZN (1954:278)]

In popular culture

Main article: Chambered Nautilus#In literature and art

The nautilus shell features prominently in the official emblem of New Caledonia.

See also

• Cephalopod size, for maximum shell diameters
• History of animals by Conrad Gesner, first book with fossil illustrations.
• The Nautilus, a malacological journal
• The Chambered Nautilus, a poem of Oliver Wendell Holmes

References

1. ^ Ward; Saunders (1997). "Allonautilus: A New Genus of Living Nautiloid Cephalopod and Its Bearing on Phylogeny of the Nautilida". Journal of Paleontology (Paleontological Society) 71 (6): 1054–1064. doi:10.2307/1306604. JSTOR 1306604.  edit
2. ^ ^{a b} Kümmel,B. 1964. Nautiloidae-Nautilida, in the Treatise on Invertebrate Paleontology, Geological Society of America and Univ of Kansas Press, Teichert and Moore eds.
3. ^ Wingstrand, KG (1985). "On the anatomy and relationships of Recent Monoplacophora" (Link to free full text + plates). Galathea Rep. 16: 7–94. http://www.zmuc.dk/inverweb/Galathea/Galathea_p5.html. 
4. ^ "Diagenesis of aragonite from Upper Cretaceous ammonites: a geochemical case-study". Sedimentology 28 (3): 423–438. 1981. Bibcode 1981Sedim..28..423B. doi:10.1111/j.1365-3091.1981.tb01691.x.  edit
5. ^ ^{a b c} Willey, Arthur (1897). "The Pre-ocular and Post-ocular Tentacles and Osphradia of Nautilus". Quarterly Journal of Microscopical Science 40 (1): 197–201. http://jcs.biologists.org/content/vols2-40/issue157/. 
6. ^ Fukuda, Y. 1987. Histology of the long digital tentacles. In: W.B. Saunders & N.H. Landman (eds.) Nautilus: The Biology and Paleobiology of a Living Fossil. Springer Netherlands. pp. 249–256. doi:10.1007/978-90-481-3299-7_17
7. ^ Kier, W.M. 1987. The functional morphology of the tentacle musculature of Nautilus pompilius.PDF In: W.B. Saunders & N.H. Landman (eds.) Nautilus: The Biology and Paleobiology of a Living Fossil. Springer Netherlands. pp. 257–269. doi:10.1007/978-90-481-3299-7_18
8. ^ Grasso, F.; Basil, J. (2009). "The evolution of flexible behavioral repertoires in cephalopod molluscs". Brain, Behavior and Evolution 74 (3): 231–245. doi:10.1159/000258669. PMID 20029186.  edit
9. ^ Saunders WB (June 1984). "Nautilus Growth and Longevity: Evidence from Marked and Recaptured Animals". Science 224 (4652): 990–992. doi:10.1126/science.224.4652.990. PMID 17731999. 
10. ^ Dunstan AJ; Ward PD; Marshall NJ (February 2011). "Nautilus pompilius life history and demographics at the Osprey Reef Seamount, Coral Sea, Australia.". PLoS One 6 (2): e16312. doi:10.1371/journal.pone.0016312. http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0016312. 
11. ^ Broad WJ (24 October 2011). "Loving the Chambered Nautilus to Death". New York Times. http://www.nytimes.com/2011/10/25/science/25nautilus.html?_r=4. Retrieved 25 October 2011. 
12. ^ Dunstan AJ; Bradshaw CJA; Marshall NJ (February 2011). "Nautilus at Risk – Estimating Population Size and Demography of Nautilus pompilius.". PLoS One 6 (2): e16716. doi:10.1371/journal.pone.0016716. http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0016716. 
13. ^ 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.
• Nautilus: the biology and palaeontology of a living fossil. ISBN 978-90-481-3299-7. http://www.springerlink.com/content/978-90-481-3298-0/#section=639864&page=10&locus=96. 
• CephBase: Nautilidae

External links

• Nautilidae discussion forum, tonmo.com
• Waikïkï Aquarium: Marine Life Profile: Chambered Nautilus, waguarium.org
• A molecular and karyological approach to the taxonomy of Nautilus, utmb.edu