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The nautilus (, ) is a
pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or w ...
marine
mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000  extant species of molluscs are recognized. The number of fossil species is est ...
of the
cephalopod A cephalopod is any member of the molluscan class Cephalopoda ( Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...
family Nautilidae. The nautilus is 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 chambered nautilus (''Nautilus pompilius''), also called the pearly nautilus, 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 ...
'', the name
chambered nautilus The chambered nautilus (''Nautilus pompilius''), also called the pearly nautilus, 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 also used for any of the Nautilidae. All are protected under CITES Appendix II. Depending on species, adult shell diameter is between 4 and 10 inches. Nautilidae, both extant and extinct, are characterized by
involute In mathematics, an involute (also known as an evolvent) is a particular type of curve that is dependent on another shape or curve. An involute of a curve is the locus of a point on a piece of taut string as the string is either unwrapped from o ...
or more or less convolute shells that are generally smooth, with compressed or depressed
whorl A whorl ( or ) is an individual circle, oval, volution or equivalent in a whorled pattern, which consists of a spiral or multiple concentric objects (including circles, ovals and arcs). Whorls in nature File:Photograph and axial plane floral ...
sections, straight to sinuous sutures, and a tubular, generally central
siphuncle The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, a ...
.Kümmel, B. 1964. Nautiloidae-Nautilida, in the
Treatise on Invertebrate Paleontology The ''Treatise on Invertebrate Paleontology'' (or ''TIP'') published by the Geological Society of America and the University of Kansas Press, is a definitive multi-authored work of some 50 volumes, written by more than 300 paleontologists, and ...
, Geological Society of America and Univ of Kansas Press, Teichert and Moore eds.
Having survived relatively unchanged for hundreds of millions of years, nautiluses represent the only living members of the subclass nautiloidea, and are often considered "
living fossil A living fossil is an extant taxon that cosmetically resembles related species known only from the fossil record. To be considered a living fossil, the fossil species must be old relative to the time of origin of the extant clade. Living foss ...
s". The word nautilus is derived from the Greek word ''nautílos'' "sailor", it originally referred to a type of octopus of the genus '' Argonauta'', also known as 'paper nautilus', which were thought to use two of their arms as sails.


Anatomy


Cirri

The "tentacles" of the nautili are actually cirri (singular: cirrus), composed of long, soft, flexible appendages which are retractable into corresponding hardened sheaths. Unlike the 8–10 head appendages of coleoid cephalopods, nautiluses have many cirri. In the early embryonic stages of nautilus development a single
molluscan Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is estim ...
foot differentiates into a total of 60–90 cirri, varying even within a species. Nautilus cirri also differ from the tentacles of some coleoids in that they are non-elastic and lack pads or suckers. Instead, nautilus cirri adhere to prey by means of their ridged surface. Nautili have a powerful grip, and attempts to take an object already grasped by a nautilus may tear away the animal's cirri, which will remain firmly attached to the surface of the object. The main cirri emerge from sheaths which cohere into a single firm fleshy mass. Also, the pair of cirri before the eye (pre-ocular) and the pair of cirri behind the eye (post-ocular) are separate from the others. These are more evidently grooved, with more pronounced ridges. They are extensively
cilia The cilium, plural cilia (), is a membrane-bound organelle found on most types of eukaryotic cell, and certain microorganisms known as ciliates. Cilia are absent in bacteria and archaea. The cilium has the shape of a slender threadlike proje ...
ted and are believed to serve an
olfactory The sense of smell, or olfaction, is the special sense through which smells (or odors) are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste. In humans, ...
purpose.


Digestive system

The
radula The radula (, ; plural radulae or radulas) is an anatomical structure used by molluscs for feeding, sometimes compared to a tongue. It is a minutely toothed, chitinous ribbon, which is typically used for scraping or cutting food before the food ...
is wide and distinctively has nine teeth. The mouth consists of a parrot-like beak made up of two interlocking jaws capable of ripping the animal's food— mostly crustaceans— from the rocks to which they are attached. Males can be superficially differentiated from females by examining the arrangement of tentacles around the buccal cone: males have a spadix organ (shaped like a spike or shovel) located on the left side of the cone making the cone look irregular, whereas the buccal cone of the female is
bilaterally symmetrical Symmetry in biology refers to the symmetry observed in organisms, including plants, animals, fungi, and bacteria. External symmetry can be easily seen by just looking at an organism. For example, take the face of a human being which has a pl ...
. The crop is the largest portion of the digestive tract, and is highly extensible. From the crop, food passes to the small muscular stomach for crushing, and then goes past a digestive caecum before entering the relatively brief intestine.


Circulatory system

Like all cephalopods, the blood of the nautilus contains hemocyanin, which is blue in its oxygenated state. There are two pairs of
gill A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they ar ...
s which are the only remnants of the ancestral metamerism to be visible in extant cephalopods. Oxygenated blood arrives at the heart through four ventricles and flows out to the animal's organs through distinct aortas but returns through veins which are too small and varied to be specifically described. The one exception to this is the vena cava, a single large vein running along the underside of the crop into which nearly all other vessels containing deoxygenated blood empty. All blood passes through one of the four sets of filtering organs (composed of one pericardial appendage and two renal appendages) upon leaving the vena cava and before arriving at the gills for re-oxygenation. Blood waste is emptied through a series of corresponding pores into the pallial cavity.


Nervous system

The central component of the nautilus nervous system is the oesophageal nerve ring which is a collection of
ganglia A ganglion is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system there are both sympathe ...
, commissures, and connectives that together form a ring around the animal's oesophagus. From this ring extend all of the nerves forward to the mouth, tentacles, and funnel; laterally to the eyes and rhinophores; and posteriorly to the remaining organs. The nerve ring does not constitute what is typically considered a cephalopod "brain": the upper portion of the nerve ring lacks differentiated lobes, and most of the nervous tissue appears to focus on finding and consuming food (i.e., it lacks a "higher learning" center). Nautili also tend to have rather short memory spans, and the nerve ring is not protected by any form of brain case.


Shell

Nautili are the sole living cephalopods whose bony body structure is externalized as a planispiral shell. The animal can withdraw completely into its shell and close the opening with a leathery hood formed from two specially folded
tentacle In zoology, a tentacle is a flexible, mobile, and elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work main ...
s. The shell is coiled, aragonitic,
nacre Nacre ( , ), also known as mother of pearl, is an organicinorganic composite material produced by some molluscs as an inner shell layer; it is also the material of which pearls are composed. It is strong, resilient, and iridescent. Nacre is ...
ous and pressure-resistant, imploding at a depth of about . The nautilus shell is composed of two layers: a
matte Matte may refer to: Art * paint with a non-glossy finish. See diffuse reflection. * a framing element surrounding a painting or watercolor within the outer frame Film * Matte (filmmaking), filmmaking and video production technology * Matte pa ...
white outer layer with dark orange stripes, and a striking white
iridescent Iridescence (also known as goniochromism) is the phenomenon of certain surfaces that appear to gradually change color as the angle of view or the angle of illumination changes. Examples of iridescence include soap bubbles, feathers, butterfl ...
inner layer. The innermost portion of the shell is a pearlescent blue-gray. The osmeña pearl, contrarily to its name, is not a
pearl A pearl is a hard, glistening object produced within the soft tissue (specifically the mantle) of a living shelled mollusk or another animal, such as fossil conulariids. Just like the shell of a mollusk, a pearl is composed of calcium carb ...
, but a
jewellery Jewellery ( UK) or jewelry ( U.S.) consists of decorative items worn for personal adornment, such as brooches, rings, necklaces, earrings, pendants, bracelets, and cufflinks. Jewellery may be attached to the body or the clothes. From a w ...
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 The Southeastern Pennsylvania Transportation Authority (SEPTA) is a regional public transportation authority that operates bus, rapid transit, commuter rail, light rail, and electric trolleybus services for nearly 4 million people in five c ...
, each of which is pierced in the middle by a duct, the
siphuncle The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, a ...
. 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 4 at the moment of
hatching Hatching (french: hachure) is an artistic technique used to create tonal or shading Shading refers to the depiction of depth perception in 3D models (within the field of 3D computer graphics) or illustrations (in visual art) by varying ...
to 30 or more in adults. The shell coloration also keeps the animal
cryptic Cryptic may refer to: In science: * Cryptic species complex, a group of species that are very difficult to distinguish from one another * Crypsis, the ability of animals to blend in to avoid observation * Cryptic era, earliest period of the Earth ...
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 Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the b ...
is called
countershading Countershading, or Thayer's law, is a method of camouflage in which an animal's coloration is darker on the top or upper side and lighter on the underside of the body. This pattern is found in many species of mammals, reptiles, birds, fish ...
. The nautilus shell presents one of the finest natural examples of a
logarithmic spiral A logarithmic spiral, equiangular spiral, or growth spiral is a self-similar spiral curve that often appears in nature. The first to describe a logarithmic spiral was Albrecht Dürer (1525) who called it an "eternal line" ("ewige Linie"). More ...
, although it is not a golden spiral. The use of nautilus shells in art and literature is covered at
nautilus shell The chambered nautilus (''Nautilus pompilius''), also called the pearly nautilus, 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 ...
.


Size

''N. pompilius'' is the largest species in the genus. One form from
Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Gui ...
and northern
Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
, once called ''N. repertus'', may reach in diameter. However, most nautilus species never exceed . '' Nautilus macromphalus'' is the smallest species, usually measuring only . A dwarf population from the
Sulu Sea The Sulu Sea ( fil, Dagat Sulu; Tausug: ''Dagat sin Sūg''; Chavacano: ''Mar de Sulu''; Cebuano: ''Dagat sa Sulu''; Hiligaynon: ''Dagat sang Sulu''; Karay-a: ''Dagat kang Sulu''; Cuyonon: ''Dagat i'ang Sulu''; ms, Laut Sulu) is a body o ...
('' Nautilus pompilius suluensis'') is even smaller, with a mean shell diameter of .


Physiology


Buoyancy and movement

To swim, the nautilus draws water into and out of the living chamber with its hyponome, which uses jet propulsion. This mode of propulsion is generally considered inefficient compared to propulsion with fins or undulatory locomotion, however, the nautilus has been found to be particularly efficient compared to other jet-propelled marine animals like
squid True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fittin ...
and
jellyfish Jellyfish and sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum Medusozoa, a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animals with umbre ...
, or even
salmon Salmon () is the common name for several commercially important species of euryhaline ray-finned fish from the family Salmonidae, which are native to tributaries of the North Atlantic (genus '' Salmo'') and North Pacific (genus '' Onco ...
at low speeds. It is thought that this is related to the use of asymmetrical contractile cycles and may be an adaptation to mitigate metabolic demands and protect against hypoxia when foraging at depth. While water is inside the chamber, the
siphuncle The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, a ...
extracts
salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quant ...
from it and diffuses it into the blood. The animal adjusts its
buoyancy Buoyancy (), or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the ...
only in long term density changes by
osmosis Osmosis (, ) is the spontaneous net movement or diffusion of solvent molecules through a selectively-permeable membrane from a region of high water potential (region of lower solute concentration) to a region of low water potential (region ...
, either removing liquid from its chambers or allowing water from the blood in the siphuncle to slowly refill the chambers. This is done in response to sudden changes in buoyancy that can occur with predatory attacks of fish, which can break off parts of the shell. This limits nautiluses in that they cannot operate under the extreme
hydrostatic pressure Fluid statics or hydrostatics is the branch of fluid mechanics that studies the condition of the equilibrium of a floating body and submerged body " fluids at hydrostatic equilibrium and the pressure in a fluid, or exerted by a fluid, on an i ...
s found at depths greater than approximately , and in fact implode at about that depth, causing instant death. The gas also contained in the chambers is slightly below atmospheric pressure at sea level. The maximum depth at which they can regulate buoyancy by osmotic removal of chamber liquid is not known. The nautilus has the extremely rare ability to withstand being brought to the surface from its deep natural habitat without suffering any apparent damage from the experience. Whereas fish or crustaceans brought up from such depths inevitably arrive dead, a nautilus will be unfazed despite the pressure change of as much as . The exact reasons for this ability, which is thought to be coincidental rather than specifically functional, are not known, though the perforated structure of the animal's
vena cava In anatomy, the venae cavae (; singular: vena cava ; ) are two large veins (great vessels) that return deoxygenated blood from the body into the heart. In humans they are the superior vena cava and the inferior vena cava, and both empty into th ...
is thought to play an important role.


Senses

Unlike many other cephalopods, nautiluses do not have what many consider to be good vision; their eye structure is highly developed but lacks a solid
lens A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements ...
. Whereas a sealed lens allows for the formation of highly focused and clear, detailed surrounding imagery, nautiluses have a simple pinhole eye open to the environment which only allows for the creation of correspondingly simple imagery. Instead of vision, the animal is thought to use
olfaction The sense of smell, or olfaction, is the special sense through which smells (or odors) are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste. In humans, ...
(smell) as the primary sense for
foraging Foraging is searching for wild food resources. It affects an animal's fitness because it plays an important role in an animal's ability to survive and reproduce. Foraging theory is a branch of behavioral ecology that studies the foraging behavi ...
and for locating and identifying potential mates. The "ear" of the nautilus consists of structures called ''
otocyst Otic vesicle, or auditory vesicle, consists of either of the two sac-like invaginations formed and subsequently closed off during embryonic development. It is part of the neural ectoderm, which will develop into the membranous labyrinth of the in ...
s'' located immediately behind the pedal
ganglia A ganglion is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system there are both sympathe ...
near the nerve ring. They are oval structures densely packed with elliptical calcium carbonate crystals.


Brain and intelligence

Nautiluses are much closer to the first cephalopods that appeared about 500 million years ago than the early modern cephalopods that appeared maybe 100 million years later ( ammonoids and coleoids). They have a seemingly simple
brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...
, not the large complex brains of
octopus An octopus ( : octopuses or octopodes, see below for variants) is a soft-bodied, eight- limbed mollusc of the order Octopoda (, ). The order consists of some 300 species and is grouped within the class Cephalopoda with squids, cuttlefish, ...
,
cuttlefish Cuttlefish or cuttles are marine molluscs of the order Sepiida. They belong to the class Cephalopoda which also includes squid, octopuses, and nautiluses. Cuttlefish have a unique internal shell, the cuttlebone, which is used for control of ...
and
squid True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fittin ...
, and had long been assumed to lack intelligence. But the cephalopod nervous system is quite different from that of other animals, and recent experiments have shown not only memory, but a changing response to the same event over time. In a study in 2008, a group of nautiluses (''N. pompilius'') were given food as a bright blue light flashed until they began to associate the light with food, extending their tentacles every time the blue light was flashed. The blue light was again flashed without the food 3 minutes, 30 minutes, 1 hour, 6 hours, 12 hours, and 24 hours later. The nautiluses continued to respond excitedly to the blue light for up to 30 minutes after the experiment. An hour later they showed no reaction to the blue light. However, between 6 and 12 hours after the training, they again responded to the blue light, but more tentatively. The researchers concluded that nautiluses had memory capabilities similar to the " short-term" and " long-term memories" of the more advanced cephalopods, despite having different brain structures. However the long-term memory capability of nautiluses was much shorter than that of other cephalopods. The nautiluses completely forgot the earlier training 24 hours later, in contrast to octopuses, for example, which can remember conditioning for weeks afterwards. However, this may be simply the result of the
conditioning Conditioning may refer to: Science, computing, and technology * Air conditioning, the removal of heat from indoor air for thermal comfort ** Automobile air conditioning, air conditioning in a vehicle ** Ice storage air conditioning, air conditio ...
procedure being suboptimal for sustaining long-term memories in nautiluses. Nevertheless, the study showed that scientists had previously underestimated the memory capabilities of nautiluses.


Reproduction and lifespan

Nautiluses reproduce by laying eggs. Gravid females attach the fertilized eggs, either singly or in small batches, to rocks in warmer waters (21-25 Celsius), whereupon the eggs take eight to twelve months to develop until the juveniles hatch. Females spawn once per year and regenerate their
gonad A gonad, sex gland, or reproductive gland is a mixed gland that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, produces sp ...
s, making nautiluses the only cephalopods to present iteroparity or
polycyclic spawning Reproduction (or procreation or breeding) is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. Reproduction is a fundamental feature of all known life; each individual org ...
. 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. At sexual maturity, the male shell becomes slightly larger than the female's. Males have been found to greatly outnumber females in practically all published studies, accounting for 60 to 94% of all recorded individuals at different sites. The lifespan of nautiluses may exceed 20 years, which is exceptionally lengthy for a cephalopod, many of whom live less than three even in captivity and under ideal living conditions. However, nautiluses typically do not reach sexual maturity until they are about 15 years old, limiting their reproductive lifespan to often less than five years.


Ecology


Range and habitat

Nautiluses are only found in the
Indo-Pacific The Indo-Pacific is a vast biogeographic region of Earth. In a narrow sense, sometimes known as the Indo-West Pacific or Indo-Pacific Asia, it comprises the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the ...
, from 30° N to 30° S latitude and 90° E to 175° E longitude. They inhabit the deep slopes of
coral reef A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of Colony (biology), colonies of coral polyp (zoology), polyps held together by calcium carbonate. Most coral reefs are built from stony corals, wh ...
s. Nautiluses usually inhabit depths of several hundred metres. It has long been believed that nautiluses rise at night to feed, mate, and lay eggs, but it appears that, in at least some populations, the vertical movement patterns of these animals are far more complex. The greatest depth at which a nautilus has been sighted is (''N. pompilius''). Implosion depth for nautilus shells is thought to be around . Only in
New Caledonia ) , anthem = "" , image_map = New Caledonia on the globe (small islands magnified) (Polynesia centered).svg , map_alt = Location of New Caledonia , map_caption = Location of New Caledonia , mapsize = 290px , subdivision_type = Sovereign st ...
, the Loyalty Islands, and
Vanuatu Vanuatu ( or ; ), officially the Republic of Vanuatu (french: link=no, République de Vanuatu; bi, Ripablik blong Vanuatu), is an island country located in the South Pacific Ocean. The archipelago, which is of volcanic origin, is east of ...
can nautiluses be observed in very shallow water, at depths of as little as . This is due to the cooler surface waters found in these southern hemisphere habitats as compared to the many equatorial habitats of other nautilus populations – these usually being restricted to depths greater than . Nautiluses generally avoid water temperatures above .


Diet

Nautiluses are scavengers and opportunistic predators. They eat molts of
lobster Lobsters are a family (Nephropidae, synonym Homaridae) of marine crustaceans. They have long bodies with muscular tails and live in crevices or burrows on the sea floor. Three of their five pairs of legs have claws, including the first pair, ...
s, hermit crabs, and
carrion Carrion () is the decaying flesh of dead animals, including human flesh. Overview Carrion is an important food source for large carnivores and omnivores in most ecosystems. Examples of carrion-eaters (or scavengers) include crows, vultures ...
of any kind.


Evolution

Fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
records indicate that nautiloids 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 Late
Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ago ...
period and became a significant group of sea
predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill t ...
s during the
Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. T ...
period. Certain species reached over in size. The other cephalopod subclass, Coleoidea, diverged from the nautiloids long ago and the nautilus has remained relatively unchanged since. Nautiloids were much more extensive and varied 200 million years ago.
Extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
relatives of the nautilus include
ammonite Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefis ...
s, such as the
baculite ''Baculites'' ("walking stick rock") is an extinct genus of cephalopods with a nearly straight shell, included in the heteromorph ammonites. The genus, which lived worldwide throughout most of the Late Cretaceous, and which briefly survived the ...
s and goniatites. The family Nautilidae has its origin in the Trigonocerataceae ( Centroceratina), specifically in the Syringonautilidae of the
Late Triassic The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch ...
and continues to this day with '' Nautilus'', the type genus, and its close relative, '' Allonautilus''.


Fossil genera

The fossil record of Nautilidae begins with '' Cenoceras'' in the Late Triassic, a highly varied genus that makes up the
Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...
''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 The Middle Jurassic is the second Epoch (geology), epoch of the Jurassic Period (geology), Period. It lasted from about 174.1 to 163.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relatively ...
and is followed by the
Upper Jurassic The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987. In European lithostratigraphy, the name ...
-
Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...
'' Eutrephoceras''. '' Eutrephoceras'' is generally subglobular, 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 Lower may refer to: * Lower (surname) * Lower Township, New Jersey *Lower Receiver (firearms) * Lower Wick Gloucestershire, England See also *Nizhny Nizhny (russian: Ни́жний; masculine), Nizhnyaya (; feminine), or Nizhneye (russian: Н� ...
'' Strionautilus'' from
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
and the European ex-
USSR The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen nati ...
, 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 Crimea, crh, Къырым, Qırım, grc, Κιμμερία / Ταυρική, translit=Kimmería / Taurikḗ ( ) is a peninsula in Ukraine, on the northern coast of the Black Sea, that has been occupied by Russia since 2014. It has a p ...
and in
Libya Libya (; ar, ليبيا, Lībiyā), officially the State of Libya ( ar, دولة ليبيا, Dawlat Lībiyā), is a country in the Maghreb region in North Africa. It is bordered by the Mediterranean Sea to the north, Egypt to the east, Suda ...
. '' Carinonautilus'' is a genus from the
Upper Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...
of
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
, 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. ''
Obinautilus ''Obinautilus'' is an extinction, extinct genus of shelled cephalopod that has been variously identified as an Argonautidae, argonautid octopus, octopodMartill, D.M. & M.J. Barker (2006). A paper nautilus (Octopoda, ''Argonauta'') from the Miocen ...
'' has also been placed in Nautilidae by some authorities, though it may instead be an argonautid
octopus An octopus ( : octopuses or octopodes, see below for variants) is a soft-bodied, eight- limbed mollusc of the order Octopoda (, ). The order consists of some 300 species and is grouped within the class Cephalopoda with squids, cuttlefish, ...
.


Taxonomy

The family Nautilidae contains up to six
extant Extant is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Extant taxon, a taxon which is not extinct, ...
species and several
extinct species This page features lists of extinct species, organisms that have become Extinction, extinct, either in the wild or completely disappeared from Earth. In actual theoretical practice, a species not definitely located in the wild in the last fifty ...
: *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'' Recent genetic data has pointed to there being only three extant species: ''A. scrobiculatus'', ''N. macromphalus'', and ''N. pompilius'', with ''N. belauensis'' and ''N. stenomphalus'' both subsumed under ''N. pompilius'', possibly as
subspecies In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics ( morphology), but that can successfully interbreed. Not all specie ...
.


Dubious or uncertain taxa

The following
taxa In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...
associated with the family Nautilidae are of uncertain taxonomic status:


Conservation status and human use

Nautilus are collected or fished for sale as live animals or to carve the shells for souvenirs and collectibles, not for just the shape of their shells, but also the nacreous inner shell layer, which is used as a
pearl A pearl is a hard, glistening object produced within the soft tissue (specifically the mantle) of a living shelled mollusk or another animal, such as fossil conulariids. Just like the shell of a mollusk, a pearl is composed of calcium carb ...
substitute. Nautilus shells were popular items in the
Renaissance The Renaissance ( , ) , from , with the same meanings. is a period in European history marking the transition from the Middle Ages to modernity and covering the 15th and 16th centuries, characterized by an effort to revive and surpass ide ...
and
Baroque The Baroque (, ; ) is a style of architecture, music, dance, painting, sculpture, poetry, and other arts that flourished in Europe from the early 17th century until the 1750s. In the territories of the Spanish and Portuguese empires including ...
cabinet of curiosities and were often mounted by
goldsmith A goldsmith is a metalworker who specializes in working with gold and other precious metals. Nowadays they mainly specialize in jewelry-making but historically, goldsmiths have also made silverware, platters, goblets, decorative and servicea ...
s on a thin stem to make extravagant nautilus shell cups. The low fecundity, late maturity, long gestation period and long life-span of nautiluses suggest that these species are vulnerable to over-exploitation and demand for the ornamental shell is causing population declines. The threats from trade in these shells has led to countries such as Indonesia legally protecting the chambered nautilus with fines of up to US $8,500 and/or 5 years in prison for trading in this species. Despite their legal protection, these shells were reported to be openly sold at tourist areas in Bali as of 2014. The continued trade of these animals has led to a call for increased protection and in 2016 all species in Family Nautilidae were added to CITES Appendix II, regulating international trade. File:Berlín KGM nautilus.JPG, Baroque ''nautilus cup'' of Aleksander Kęsowski, abbot of
Oliwa Oliwa ( la, Oliva; csb, Òlëwa; german: Oliva) is a northern district of the city of Gdańsk, Poland. From east it borders Przymorze and Żabianka, from the north Sopot and from the south with the districts of Strzyża, VII Dwór and Brętow ...
, 1643-1667 File:Nautilus shell carved and painted C19th Poldi Pezzoli Museum.jpg, Nautilus shell carved and painted with fanciful scenes of human figures and animals (spider, dragonfly, dog, butterfly, sawfly, fly), bronze pendant mount, nineteenth century. Poldi Pezzoli Museum, Milan File:A Bowing in Art 1996.jpg, Nautilus shell in art 1996


See also

* Cephalopod size, for maximum shell diameters * '' Historiae animalium'' by Conrad Gessner, first book with fossil illustrations * '' The Nautilus'', a malacological journal * ''The Chambered Nautilus'', a poem of Oliver Wendell Holmes *
Nautilus Pompilius The chambered nautilus (''Nautilus pompilius''), also called the pearly nautilus, 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 ...
, a Russian rock band


References


Notes


Bibliography

* Ward, P.D. 1988. ''In Search of Nautilus''. Simon and Schuster. *


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 {{Authority control Articles containing video clips Extant Triassic first appearances