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Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Order: Nautilida
Family: Nautilidae
Genus: Nautilus
Species: pompilius
The Chambered Nautilus, Nautilus pompilius, is the most well-known nautiloid in
the world. A true living fossil, The Chambered Nautilus is a member of Class Cephalopoda which first appeared in the Cambrian around 530 million years ago (Ma). 416 Ma during the mid-Paleozoic, cephalopods diverged into nautiloids and coleoids - the squids, cuttlefish, and octopods (Kroger, 2011). Fossil evidence has shown that extant Nautilus is highly conserved and more morphologically similar to the first shelled cephalopods than coleoids that derived later - this is why it is regarded as a "living fossil".
Whereas coleoids evolved to have an internal shell or no shell at all, Nautilus lives in a continually growing two-layered shell composed of chambers (called a phragmocone) arranged in a spiral. Since hatching, Nautilus pompilius has a 7-chambered shell. As it grows it seals the previous chamber with a calcareous secretion and the animal moves to fill the new larger open space. This process continues until fully grown with approximately 39 chambers. The chambers are connected by a duct in the center called a siphuncle which helps regulate pressure inside the chambers to regulate buoyancy. N. pompilius is the largest of the extant Nautiloids reaching up to 26.8cm in diameter (Kroger, 2011).
The long gestation period, low fecundity, slow movement, and restriction of habitat makes N. pompilius susceptible to over-exploitation. Shell-collection, jewelry, and overfishing (intentional or not) have contributed to the species' declining population (Dunstan, et al 2011). As of October 2016, the United Nations Convention on International Trade in Endangered Species adopted Nautilus pompilius into Appendix 2 designation, resulting in higher protection from trade demand (Broad, 2011).
Citations
Broad, William (24 October 2011). "Loving the Chambered Nautilus to Death". The New York Times.
Castrejón Pita, A. A., et al. "The impressive complexity in the Nautilus pompilius shell." Fractals 11.02 (2003): 163-168.
Dunstan, Andrew J., Peter D. Ward, and N. Justin Marshall. "Nautilus pompilius life history and demographics at the Osprey Reef Seamount, Coral Sea, Australia." PloS one 6.2 (2011).
Dunstan, Andrew, Corey JA Bradshaw, and Justin Marshall. "Nautilus at risk–estimating population size and demography of Nautilus pompilius." PloS one 6.2 (2011).
Kier, W.M. 1987. "The functional morphology of the tentacle musculature of Nautilus pompilius."In: W.B. Saunders & N.H. Landman (eds.) Nautilus: The Biology and Paleobiology of a Living Fossil. Springer Netherlands. pp. 257–269.
Kröger, Björn, Jakob Vinther, and Dirk Fuchs. "Cephalopod origin and evolution: a congruent picture emerging from fossils, development and molecules." Bioessays 33.8 (2011): 602-613.
Sousounis, Konstantinos, Atsushi Ogura, and Panagiotis A. Tsonis. "Transcriptome analysis of nautilus and pygmy squid developing eye provides insights in lens and eye evolution." PloS one 8.10 (2013).
Von Byern, Janek, et al. "Old and sticky—adhesive mechanisms in the living fossil Nautilus pompilius (Mollusca, Cephalopoda)." Zoology 115.1 (2012): 1-11.
Wells MJ, O'Dor RK. 1991. Jet propulsion and the evolution of the Cephalopods. Bull Mar Sci 49: 419–32.
Nautiloids rely on "shell-pumping" or jet propulsion for movement. It draws water in through a siphon called a hyponome into the chamber the organism lives in and pumps water out to generate propulsion, although it is slow (Wells, 1991). N. pompilius modifies its buoyancy by osmosis and extracts water or adds water to its chambers. Unlike squids and octopus, Nautilus has a pin-hole type of eye that lacks a lens and cornea (Sousounis, et al 2013). This means that the vision of Nautilus is more simple than other cephalopods.
Rather than relying solely on vision, Nautilus probably uses chemical olfaction to find food and to mate. Two pairs of tentacles, the pre-ocular and post-ocular, are different from the rest of the organism's tentacles; they are cilliated and serve as olfactory organs (Kier, 1987). The rest of the tentacles - of which there may be up to 90 - are flexible and used for touching and feeding. Nautilus tentacles lack suckers or hooks but instead glands on the oral side of the tentacles produce a glue for chemical adhering (Byern, et al 2012).
Environment and Reproduction
Nautilus pompilius is benthic and likes to live on the slopes of coral reefs in the oceans of the Indo-Pacific at depths greater than 100m. They generally avoid warm water temperatures above 25 degrees C. The shell of N. pompilius limits the depths the organism can live as it implodes around 800m depth due to the high pressures (Pita, et al). The deepest recorded N. pomilius was found at 703m (Dunstan, et al 2011). N. pompilius typically undergoes vertical movement to shallower waters (around 200m) during the nighttime to feed and stays in the deeper waters during the day to avoid predation. As Nautiliods do not produce larvae, they are restricted from colonizing over distances in open ocean. The shell of N. pompilius exhibits countershading - it is patterned dark dorsally and white ventrally to provide camouflage in the ocean (Pita, et al).
N. pompilius can have a very long lifespan for a cephalopod and may live to 20 years or more. Development and sexual maturity is late and may take 12-15 years (Pita, et al). N. pompilius has low fecundity and long gestation times - 10 to 12 months while only producing 10-20 viable eggs per year (Dunstan, et al 2011). There has been no direct observation of egg-laying or embryonic development in wild populations and most of what we know comes from aquarium settings. Demographic studies of N. pompilius show local populations to be low in overall number and density, high in mature individuals, with a high percentage of males (60-94%) (Dunstan, et al 2011).
Locomotion and Sensory Systems
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