Nautilus+pompilius

Chambered Nautilus //Nautilus pompilius// Linnaeus, 1758 toc The most beautiful thing we can experience is the mysterious. It is the source of all true art and science." - Einstein, Albert. Photo credit: MarineBio. (Pending approval)

1. Introduction
Nautiluses are cephalopods (Greek for “head-foot” due to tentacles attaching to the head) that are closely related to the coleoids such as octopus, cuttlefish and squid 1]. Commonly referred to as the “living fossils”, nautiluses had originated and virtually unmodified over the last 450 million years 2]. These marine creatures have dominated the ancient oceans before the realm of fishes arose, and even before the first dinosaurs appeared. There were approximately 10,000 species in prehistoric times but only six extant species in the Nautilidae family remain as of today 1] 3]. The Chambered Nautilus (//Nautilus pompilius//) is of particular interest, being the largest and most prevalent nautilus known to exist!

Genus //Nautilus// Genus //Allonautilus//
 * //Nautilus pompilius// Linnaeus, 1758;
 * //Nautilus// //macromphalus// Sowerby, 1849;
 * //Nautilus stenomphalus// Sowerby, 1849;
 * //Nautilus belauensi//s Saunders, 1981
 * //Allonautilus scrobiculatus// (Lightfoot, 1786);
 * //Allonautilus perforates// (Conrad, 1847).

2.1. Evolutionary relationship with ammonites!
Nautiluses are often compared with ammonites due to numerous morphological similarities. In contrast to popular belief, ammonites and modern coleoids are more closely related as compared to the extant nautilus 4]. Nautiluses originated from the Ordovician period (approximately 450 million years ago) wheres ammonites first appeared during the Permian period (approximately 240 million years ago) 4]. Ammonites faced extinction after three catastrophic events during the Permian, Triassic and end of the Cretaceous, which coincided with that of dinosaurs in the Cretaceous-Palaeogene (K-Pg) event 5]. Their shells are index fossils for stratigraphy due to their easy identification, rapid evolution and being discovered on many types of marine sedimentary rocks with global geographic distribution 6]. Ammonites were believed to be petrified snakes and were fitted with carved heads to be sold to pilgrims during the medieval times 5]. Phylogenetic tree depicting relationships amongst cephalopods with stratigraphic ranges; Ammonoidea is more closely related to the coleoids as compared to Nautiloidea. Dotted lines represent no evidence to prove existence of common ancestor 7]. Images adapted from Benton & Harper, 2013. (Pending approval) Ammonite fossils arranged in chronological order (Early Jurassic - Late Cretaceous). Photo credit: British Geological Survey. (Pending approval)
 * = [[image:taxo4254/Screen Shot 2016-11-18 at 9.24.10 pm.png width="127" height="168"]] ||= [[image:taxo4254/Screen Shot 2016-11-18 at 9.24.04 pm.png width="126" height="164"]] ||= [[image:taxo4254/Screen Shot 2016-11-18 at 9.23.58 pm.png width="130" height="163"]] ||= [[image:taxo4254/Screen Shot 2016-11-18 at 9.23.52 pm.png width="137" height="182"]] ||= [[image:taxo4254/Screen Shot 2016-11-18 at 9.23.45 pm.png width="119" height="173"]] ||

Ammonite fossil with undulated sutures. Photo credit: The Crystal Caves, used with permission.
 * Table 1.** Comparison of anatomical and physiological features between modern nautilus and ammonite fossils 8]
 * **Cephalopods** || **Siphuncle** || **Shell texture; inner chambers; sutures** || **Protection mechanism** || **Camouflage** ||
 * **Modern nautilus** || Runs straight through the centre of shell || Smooth shell; 30 chambers; uniformly curved sutures || No retraction of bodies into shell; leathery hood atop the head of shell || Countershading ||
 * **Ammonite fossils** || Ran along outer edge of the shell || “Ribbed” shell; 26 chambers; undulated sutures || Retraction of bodies into shell; flap called the aptychus close at the head of shell || Colours unknown ||

2.2. The nautilus shell is not a golden spiral!
Often associated with the golden spiral, the nautilus shell is in fact an equiangular spiral. The golden spiral ratio is a beautiful logarithm of 1.618:1 whereas the average ratio of nautilus shell is 1.33:1 9]. Golden spiral (blue solid lines) superimposed on Nautilus equiangular spiral shell. Photo credit: Gary Meisner, 2014.

**3.1. Native distribution range**
The occurrence of //Nautilus// //pompilius// subspecies exist in different regions - //Nautilus pompilius pompilius// covers the Andaman Sea east to Fiji and southern Japan south to the Great Barrier Reef whereas //Nautilus pompilius suluensis// is restricted to the Sulu Sea in southwestern Philippines 10].

Geographic distribution map of //Nautilus// populations indicated by red dots. Image adapted from Encyclopedia of Life 11]. Close-up of geographic distribution map of //Nautilus// populations: (1) Philippines; (2) Great Barrier Reef, Australia; (3) Vanuatu, South Pacific Ocean; (4) Fiji, South Pacific Ocean; (5) American Samoa. Image adapted from Vandepas et al. 2016.

3.2. Singapore context
Few captive specimens currently reside in S.E.A. Aquarium 12]. However, no wild live specimens have been recorded in Singapore to date 13]. Only fragmented empty shell pieces have been retrieved until a complete nautilus shell was discovered on [|Pulau Semakau] in a preliminary survey conducted in 2010 14] 15]. The origin of this particular shell is undetermined yet. This finding raised questions on whether there could be a population near, if not in Singapore waters. Unfortunately, such a hypothesis may disappoint many due to (1) transportation by currents or (2) extensive involvement in ornamental shell trade and could be an accidental discovery! (Left) A live specimen of //Nautilus pompilius// in S. E.A. Aquarium. Image taken by Gan Zi Hui. (Right) Complete postmortem shell of //Nautilus pompilius// discovered in Singapore. Photo credit: Ron Yeo. (Pending approval)
 * [[image:IMG_5035.JPG width="252" height="192" align="left"]] || [[image:taxo4254/nautilus.jpg width="276" height="195" align="left"]] ||

4. Threats & Conservation Status!
Identification of species within //Nautilus// is of great significance due to their vulnerability and susceptibility to commercial harvest in ornamental shell trade 16]. At present, there exists legislative protection for populations in Great Barrier Reef and local agreement with fishermen not to target populations in the Coral Sea (Australian regulatory authorities for additional protective measures - Marine Bioregional Planning of Coral Sea) 17]. Some countries such as Indonesia have banned their export since 1987. Furthermore, there is legal protection under Schedule 1, Appendix Part IV(B) Mollusca of Wildlife Protection Act, 1972.

In contrast, there is absence of such protective legislation in several regions such as the Philippines. They are not yet under the protection of U.S. Fish and Wildlife Service (USFWS), not evaluated for International Union for Conservation of Nature (IUCN) Red List of Threatened Species and not yet listed on Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) 18]. Fortunately, there are petitions to review and list chambered nautiluses under Appendix II 19]. Long-term effects of //Nautilus// overfishing are unexplored but protective measures are key to conservation of this unique species. Bamboo traps used to capture chambered nautilus. Photo credit: Jürgen Freund and WWF/TRAFFIC. (Pending approval)

5.1. Habitat
Chambered nautiluses occur at coral reef slopes of tropical and warm temperate waters in Indo-Pacific region. Being benthic bottom dwellers, they can dive to depths of 600-2000 feet 1]. Yet, there is a depth limit for these deep sea creatures where the deepest record was 2300 feet 20]. They are subjected to severe stress during rapid ascent and descent through the water column. An experiment conducted in 1980 resulted in the implosion of the ectosiphuncule, which is the weakest of all shell components, which occurred at depths of 2575 feet (hydrostatic pressure of 8.05MPa) 21] 22].

5.2. Locomotion and Buoyancy
1. Diel vertical migration Having said that chambered nautiluses can ascend and descent through different oceanic zones, they undergo diurnal migration to deeper waters (600-2000 feet) to avoid predation and nocturnal migration up to coral reefs (300 feet) to hunt for prey 23]. To control positive, negative or neutral buoyancy while maintaining an upright position, the ratio of argon-nitrogen gas mixture and liquid saline solution in the inner chambers connected to ectosiphuncle is modified, and thus its weight, for diving 24].

2. Jet propulsion Similar to other coleoids, chambered nautiluses move via jet propulsion. They exhibit a see-saw motion by alternately drawing water into its mantle cavity and blowing it out through the muscular, elastic siphon beneath the tentacles. This way, the forward, backward and sideways movements can be controlled 24].

media type="youtube" key="hcyzr3zJol4" width="560" height="315" align="center" Locomotion of the chambered nautilus. Video adapted from Youtube Channel: "The Chambered Nautilus" 25] Hyponome of the chambered nautilus, where water is blown out and results in jet propulsion. Photo credit: David Remsen, Flickr 26]

5.3. Reproduction, Growth and Sexual Maturity
Chambered nautiluses are gonochoristic organisms, indicating that the species have separate sexes. The male/female ratio is 8:1 and <10% are juveniles in unexploited populations 16]. Researchers have speculated that the male-biased sex ratio is (1) a reflection of the natural equilibrium of these populations and is the critical sex for its population growth or (2) due to sampling bias 27].

Methods used to determine their sexes 23]: 1. Newly caught nautiluses which are not accustomed to captivity can be turned upside down. A visible horseshoe-shaped gland is found in females and will be brownish green in mature individuals. This method should only be performed by trained aquarists. 2. Locate the spadix (large modified tentacle made out of 4 tentacles) which should only be found on the left side in males.

Little is known about their reproductive means in the wild, and their mating behaviour is only observed in protected captivity 24]. Through internal fertilization, males transfer a sperm packet (i.e. spermatophore) via the spadix into the mantle cavity of females while holding onto their shell 2]. Each female lays 20 oblong eggs (largest amongst all cephalopods) and attaches the eggs to solid surfaces. The eggs are covered with membrane layers that form a protective covering. Development of the embryo lasts for 9-12 months before hatching 3]. Chambered nautiluses do not undergo larval stage and new hatchlings have four inner chambers. As they grow larger, septa are produced to seal off older chambers.


 * Table 2.** Comparison of reproductive features between nautilus and coleoids
 * **Cephalopods** || **Sexual maturity** || **Reproductive strategy** || **Lifetime reproductive rate** ||
 * **Nautilus** || Long; average of 10-15 years || k selection 27]; long gestation periods and low offspring numbers || Multiple times; once per year ||
 * **Coleoids** || Short || r selection 28]; short gestation periods and high offspring numbers || Once ||

5.4. Memory
Unlike modern cephalopods that have diverged from the primitive nautilus and evolved large brains for long term memory, chambered nautiluses have lack thereof brain structures. Nevertheless, a research study resembling Pavlov’s experiments with dogs demonstrated some evidence of a simple form of memory in chambered nautiluses 29] 30].

media type="youtube" key="usDqXrT7zso" width="560" height="315" align="center" Video adapted from Youtube Channel: "Simple minded nautilus reveals flash of memory"

5.5. Feeding
As opportunistic feeders, chambered nautiluses’ diet consists of high calcium food sources such as crustaceans and their molts, nematodes, echinoids, fishes to sustain normal shell growth 23]. They are also obligate scavengers, feeding on dead organisms (i.e. carrion) which is crucial for recycling of nutrients. At times, they even resort to cannibalism whereby cephalopod beaks and nautilus tentacles were found in their gut. Due to their poor vision, they locate prey via olfaction or specifically, chemotaxis 31]. They possess a pair of rhinopores to sample lateral currents for detecting chemical trails.

5.6. Natural predators
Octopus, sharks, triggerfish, sea turtle prey on the chambered nautilus 1].

6. Description
Anatomical features of a nautilus. Image adapted from Benton & Harper, 2013. (Pending approval) The shell is underlined with compartmentalized chambers that are separated by septum walls. An individual can possess an average of 30 chambers by adulthood. Its entire body is contained within the outermost compartment, being the newest and largest 23]. Chambers are interconnected by an ectosiphuncule that is used for locomotion.
 * Anatomy & Physiology**
 * Internal compartmentalized chambers**

Nautiluses are the only cephalopods with an equiangular spiral external shell made of calcium carbonate produced by its mantle 23] 24]. Brown stripes radiate in an irregular pattern from umbilicus (approximately 5% of shell diameter) to venter 31]. Colouration (i.e. amount, hue, degree of coalescence of banding over the venter and band development near the umbilicus) is variable. An umbilical callus is secreted during the growth of second whorl, with rare exceptions of an open umbilicus. The leathery hood is situated above its body which is used for concealing itself at times of dangerous threats 23].
 * Spiral external shell and leathery hood**

Functions of external shell 23]: 1. Protection: Nautilus withdraws its body into its shell completely and covers the opening with the leathery hood at times of threats. 2. Countershading: To avoid predators, the dark dorsal region of the shell blends in with the darkness of the sea when observed from above, while the light ventral region of the shell blends in with light penetration when observed from below.

Nautiluses possess more than 90 suckerless, retractable tentacles. These arm-like appendages have alternating grooves and ridges that are used to grip onto prey prior to delivering it to its beak-like jaw. The radula (file-like feeding structure) further shreds its prey before swallowing 1].
 * Tentacles and feeding organs**


 * Table 3.** Comparison of anatomical and physiological features between nautilus and coleoids
 * **Cephalopods** || **Life Span** || **Vision** || **Chromatophores and ink sac** || **Pairs of gills; and their attachment** 32] ||
 * **Nautilus** || Long; average of 20 years || Poor vision due to simple, primitive eyes and absence of lenses || Absent; thus poor camouflage || Two; Single attachment at the origin and lie freely in the mantle cavity ||
 * **Coleoids** || Short; average of 1-2 years || Excellent vision || Present || One; Attachment along the body wall at one side ||

7. Diagnosis
//Nautilus pompilius// have high morphological resemblance to other species in the Nautilidae family. Nevertheless, there are unique diagnostic features to differentiate each of the species.

1a. Umbilicus small, or moderate, i.e. from 5-16% of shell diameter, whorl cross-section oval… //Nautilus// 1b. Umbilicus larger, approximately 20% of shell diameter, whorl cross-section quadrate… //Allonautilus//
 * Dichotomous key to two genera of the family Nautilidae**

Lateral view of //Nautilus// (top left) and //Allonautilus// (top right); note the size of umbilicus in both genera. Cross section of //Nautilus// oval whorl (bottom left) and //Allonautilus// quadrate whorl (bottom right). Image adapted from FAO Species Catalogue for Fishery Purposes, used with permission 33]. ii. Callus present on umbilicus. || Maximum of 229 mm || Refer here. || ii. Callus absent. || Maximum of 160 mm || Southwestern Pacific Ocean || ii. Hood covered by elevated papillae. iii.Callus absent. || 170 mm || Great Barrier Reef of eastern Australia || ii. Longitudinally growth lines with distinct concentrically lirate pattern on shell. iii.Wide central radular teeth. || 226 mm || Pulau, Western Caroline Islands of North Pacific Ocean || Fuzzy nautilus || i. Larger umbilicus. ii. Creases and encrusting layer on periostracum. iii. Different gills and male reproductive system from //Nautilus// species. || 180 mm || Tropical western Pacific – Papua New Guinea, Manus Province, Bismark Archipelago, Milne Bay.
 * Table 4.** Diagnostic features and geographic distribution of six extant species in the family Nautilidae. Due to lack of reliable sources, no images of each //Nautilus// species are illustrated below.
 * **Accepted scientific name** || **Vernacular name(s)** || **Brief description** || **Size of shell diameter** || **Geographical distribution** ||
 * //Nautilus pompilius// || Chambered nautilus; Emperor nautilus; Pearly nautilus 34] || i. No inner shell coils visible.
 * //Nautilus// //macromphalus// || Bellybutton nautilus || i. Inner shell coils visible.
 * //Nautilus// //stenomphalus// || White-patch nautilus || i. Reduced colouration in umbilicus region.
 * //Nautilus// //belauensis// || Pulau nautilus || i. Large mature size.
 * //Allonautilus// //scrobiculatus// || Crusty nautilus;

Drift shells at Solomon Islands. ||
 * //Allonautilus perforates// || N/A || i. Shell similar to //Allonautilus scrobiculatus// || Maximum of 180 mm || Bali, Indonesia ||

8. Etymology
The term "Nautilus" is coined in Greek Ναυτίλος (pronounced as nautilos) and refers to "paper nautilus" which literally means "sailor". The ancient Greeks thought that the webbed arms were used as sails 35].

9.1. Original description
The [|original description] of //Nautilus pompilius// was retrieved from Biodiversity Heritage Library on 1 November 2016 36]. The book collection is titled "Systema Naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Editio decima, reformata. Laurentius Salvius: Holmiae. ii, 824 pp." Specifically, the description can be found on page 709:

Image adapted from book collection "Systema Naturae" by Linnaeus (1758).

9.2. Taxonavigation
The hierarchical ranks are referenced from Integrated Taxonomic Information System 37] and World Register of Marine Species (WoRMS) 38]. Ranks are not included in the classification because they do not provide meaningful information.
 * Animalia ||
 * Bilateria ||
 * Protostomia ||
 * Lophozoa ||
 * Mollusca ||
 * Cephalopoda Cuvier, 1797 ||
 * Nautiloidea Agassiz, 1847 ||
 * Nautilida Agassiz, 1847 ||
 * Nautilidae de Blainville, 1825 ||
 * //Nautilus// Linnaeus, 1758 ||
 * //Nautilus pompilius // ||
 * //Nautilus pompilius pompilius// Linnaeus, 1758 ||
 * //Nautilus pompilius suluensis// Habe and Okutani, 1988 ||

**9.3. Type Information**
The type series of //Nautilus pompilius// comprises one specimen in the Linnean Society of London, four specimens in the University Museum in Uppsala and those figured by pre-Linnean authors such as Rumphius (1705) referenced in Linnaeus (1758) 39].

Even though Linnaeus did not specifically mention any of the extant specimens in London and Uppsala, they were possibly known to him during the publication of the 10th edition of Systema Naturae (Linnaeus 1758).

Despite popular belief that the lectotype figured by Rumphius (1705) in his collection titled "D'Amboinsche Rariteitkamer" was designated by Linnaeus (1767), this assumption is invalid because no particular specimen was deemed to be the type specimen by Linnaeus himself. The specific description can be found on page 59-66 ([|http://www.biodiversitylibrary.org/item/127485#page/132/mode/2up]). Subsequent lectotypifications of Rumphius' drawings are invalid due to the fact that three different specimens are illustrated 40].

Nevertheless, a lectotype from Linnaeus' collection can be designated. An alternative approach is to apply to International Commission on Zoological Nomenclature (ICZN) to disregard all preceding designations and assign a neotype of known origin based on molecular techniques given the quality of the specimens and uncertainty to its type status 39].

**9.4. Phylogeny**
Within the Class Cephalopoda, the evolutionary history of these "living fossils" dates back to the Ordovician period and has remained unchanged over the last 450 million years. Modern coleoids and extinct ammonites had diverged from their common ancestor (//Plectronoceras//) to form distinct lineages [4].

Within the family //Nautilidae//, //Nautilus// and //Allonautilus// (previously known as //N. scrobiculatus//; genus renamed by Ward and Saunders, 1997) have high probabilities of having sister taxon relationship 41] 42]. However, there is no consensus of the phylogenetic classification of //Nautilus// to date. The taxonomic confusion (i.e. number of species in genus //Nautilus// and taxonomic status of //N. pompilius//) was due to poor recent fossil record and the proposed new species were originally collected and described from drift shells transported at extreme distances by surface currents (Refer to diagnosis for unique shell morphologies) 43].


 * Table 5.** Examples of research analyses in attempts to resolve phylogenetic classification of //N. pompilius//
 * **Analysis methodologies** || **Research authors, Year** || **Independent lineages within //N. pompilius//?** ||
 * Maximum likelihood, neighbor joining trees, fossil evidence || Wray et al., 1995 || No ||
 * Karotyping (18S rDNA) || Bonnaud, Ozouf-Costaz & Boucher-Rodoni, 2004 44] || No ||
 * Simultaneous analysis, maximum parsimony, genetic distance estimation, population aggregation analysis || Bonacum et al., 2011 || Yes ||
 * Optimal nucleotide substitution model, Bayesian inference || Vandepas et al., 2016 || No ||

Some researchers suggest that individuals from different populations may be morphotypes or subspecies, or even have phenotypic plasticity. Differences in morphological features without the creation of new species could have occurred due to environmental factors such as geographic boundaries and oceanographic conditions. The evidence of samples from different localities distributing amongst //N.////pompilius// samples may indicate that there is no reproductive isolation and thus likelihood of gene flow amongst these populations is high 42].

Other studies have shown cryptic diversity under //N. pompilius// where there are potentially up to five distinct species. Long distance migration was unlikely due to physiological and depth constraints such as reef slope lifestyle and dispersal limitations 43]. As such, reproductive isolation amongst these populations could have occurred, leading to formation of new species. The fact that these populations are discovered in different geographic localities indicates the occurrence of migrations, though the process as to how these migrations came about is unclear. It has been suggested that events such as glacial ocean movements and large scale disturbances such as cyclones could have led to such migrations over geological time scale.

Based on the above-mentioned phylogenetic analyses (morphological and molecular data), //N. stenomphalus//, //N. macromphalus//, //N. belauensis// and //N. pompilius// from various geographic localities should fall under the same clade.

Phylogenetic reconstruction of Nautilus populations using //N. scrobiculatus// (now //Allonautilus scrobiculatus//) as outgroup; unordered characters; 100 random addition heuristic searches in parsimony analyses. Image adapted from Wray et al., 1995.

10. Relevance to Humans

 * Art and Literature**
 * The famous poem “The Chambered Nautilus” was written by Oliver Wendell Holmes, where the original poem can be found on page 65 45].
 * A painting of "Chambered Nautilus" (1956) by Andrew Wyeth. A [|review] of the art piece speculated its reference to the "The Chambered Nautilus" poem 46].
 * Jewelry companies have designed pieces with reference to the exquisite inner chamber patterns of the nautilus shell 47].


 * Brand Names**
 * Nautilus Minerals: Canadian company to first launch deep sea mining campaign 48].
 * U.S.S. Nautilus (launched in 1954): First nuclear-powered Jules Vern’s submarine in the world 49].

11. Glossary

 * **Benthic** || Ecological zone at the lowest level of a water body such as oceans, which includes the sediment and sub-surface layers. ||
 * **Callus** || Thickened area of shell material that can cover the umbilicus (partly or completely). ||
 * **Chemotaxis** || Movement of a motile organism in response to chemical stimuli. ||
 * **Coalescence** || Two or more particles merge upon physical contact. ||
 * **Cryptic diversity** || Phenomenon where individuals have identical morphology but belong to different species. ||
 * **Diurnal** || During the day. ||
 * **Equiangular** || Having equal angles. ||
 * **Heuristic** || Trial and error. ||
 * **Hyponome** || A tube or funnel in cephalopods where water is expelled from for jet propulsion. ||
 * **Lectotype** || Physical specimen selected by a subsequent author from the syntypes (several specimens described in olden days) as type species. ||
 * **Lirate** || Thread-like grooves ||
 * **Morphotypes** || Individuals in a population (of the same species) distinguished by their morphology. ||
 * **Oblong** || Rectangle with unequal sides. ||
 * **Olfaction** || Sense of smell. ||
 * **Outgroup** || Group of organisms not belonging to the group whose evolutionary relationships are being analysed. Such a group is used for comparison to assess characters of the in-groups. ||
 * **Papillae** || White bumps on leathery hood ||
 * **Paraphyletic** || Group of organisms that descended from common evolutionary ancestor or ancestral group, but not including all of the descendants. ||
 * **Parsimony** || Simplest and best hypothesis that requires least evolutionary changes in phylogenetic tree reconstruction. ||
 * **Periostracum** || Thin organic coating at outermost layer of shell ||
 * **Phenotypic plasticity** || Ability of one genotype to produce more than one phenotypes when exposed to different environmental conditions. ||
 * **Pilgrim** || A traveler on a physical journey towards a holy place. ||
 * **Postmortem** || Dead form of an organism. ||
 * **Rhinopores** || Receptors used for detecting odours. ||
 * **Stratigraphy** || A branch in geology involved in studying rock layers and layering. ||
 * **Umbilicus** || Depression in the centre of shell whorl ||
 * **Undulated** || Wavy form or outline. ||
 * **Unordered characters** || Multistate (more than two states) morphological characters that have equal costs in phylogenetic analyses using parsimony. ||
 * **Uppsala** || Fourth largest city of Sweden. ||
 * **Whorl** || Spiral pattern. ||

12. References
[1] "Chambered Nautilus,” by George Grall. National Aquarium, n.d. URL: [] (Accessed on 1 November 2016).

[2] “Fascinating Facts About the Nautilus,” by Jennifer Kennedy. About Education, n.d. URL: [|http://marinelife.about.com/od/invertebrates/ss/9-Fascinating-Facts-About-Nautiluses.htm#showall] (Accessed on 2 November 2016).

[3] “Chambered Facts About Nautiluses,” by Mark Mancini. Mental Floss, n.d. URL: [] (Accessed on 2 November 2016).

[4] Benton, M. & Harper, D. A. T., 2013. Introduction to Paleobiology and the Fossil Record. John Wiley & Sons, Inc.

[5] “Ammonite Fossils", by The Crystal Caves, n.d. URL: @http://www.crystalcaves.com.au/infosheets/2%20Ammonite.pdf (Accessed on 1 November 2016).

[6] "Ammonites through time" by British Geological Survey. National Environment Research Council, n.d. URL: @http://www.bgs.ac.uk/discoveringGeology/time/Fossilfocus/ammonite.html (Accessed on 18 November 2016).

[7] Weston, P., 1996. How to Read an Evolutionary Family Tree. Creation, 18(3): 52.

[8] “The Differences Between Nautilus and Ammonites,” by Brenton Shields. eHow, n.d. URL: [] (Accessed on 2 November 2016).

[9] “Is the Nautilus shell spiral a golden spiral?,” by Gary Meisner. The Golden Number, 8 February 2014. URL: [] (Accessed on 9 November 2016).

[10] “Chambered Nautilus – //Nautilus pompilius//,” by Carnivora, 9 January 2012. URL: [] (Accessed on 2 November 2016).

[11] “//Nautilus pompilius// – Maps,” by Encyclopedia of Life, n.d. [] (Accessed on 2 November 2016).

[12] “Explore S.E.A. Aquarium: Ocean Journey,” by Resorts World Sentosa, n.d. URL: [] (Accessed on 2 November 2016).

[13] “Cephalopods (Phyllum Mollusca: Class Cephalopoda) of Singapore: Order Nautilida,” by Ron Yeo. The Tide Chaser, 6 December 2012. URL: @http://tidechaser.blogspot.sg/2012/12/cephalopoda-of-singapore.html (Accessed on 1 November 2016).

[14] "Project Semakau," by Lee Kong Chian Natural History Museum, n.d. URL: http://projectsemakau.rafflesmuseum.net/ (Accessed on 15 November 2016).

[15] Tan, S. K. & Yeo, R. K. H., 2010. The intertidal Molluscs of Pulau Semakau: Preliminary Results of "Project Semakau". Nature in Singapore, 3: 287-296.

[16] Valdivia, A., 2016. A Petition to List Chambered Nautilus (//Nautilus pompilius//) as Endangered or Threatened Species Under the Endangered Species Act. Center for Biological Diversity, 5-47.

[17] Williams, R. C., Newman, S. J. & Sinclair, W., 2012. DNA barcoding in //Nautilus pompilius// (Mollusca: Cephalooda): evolutionary divergence of an ancient species in modern times. Invertebrate Systematics, 26: 548-560. doi: 10.1071/IS12023

[18] “Pearly nautilus may get extra protection,” by K. S. Sudhi. The Hindu, 4 April 2016. URL: [] (Accessed on 9 November 2016).

[19] “Inclusion of the Family Nautilidae (Blainville, 1825) in Appendix II in accordance with Article II paragraph 2(a) of the Convention and satisfying Criterion B in Annex 2a of Resolution Conf. 9.24 (Rev. CoP16),” by Convention on International Trade in Endangered Species of Wild Fauna and Flora, 24 September – 5 October 2016. URL: [] (Accessed on 9 November 2016).

[20] Dunstan, A. J., Ward, P. D. & Marshall, N. J., 2011. Vertical Distribution and Migration Patterns of //Nautilus pompilius.// PloS ONE, 6(2): e16311. doi: 10.1371/journal.pone.0016311

[21] Kanie, Y., Fukuda, Y., Nakayama, H., Seki, K. & Hattori, M., 1980. Implosion of living //Nautilus// under increased pressure. Paleobiology, 6(1): 44-47.

[22] Saunders, W. B. & Wehman, D. A. (1977). Shell strength of //Nautilus// as a depth limiting factor. Paleobiology, 3: 83-89.

[23] “Aquarium Science: Husbandry of the Nautilus: Aspects of its Biology, Behaviour, and Care,” by Adam Daw and Gregory J. Barord. Tropical Fish Magazine, June 2007. URL: [] (Accessed on 2 November 2016).

[24] “Chambered Nautilus,” by Aquarium of the Pacific, n.d. URL: [] (Accessed on 1 November 2016).

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