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NAUTILUS

Note 2

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REPRODUCTION AND GROWTH OF THE SMALL

From the observation in the aquarium it has been observed that they reach sexual maturity no earlier than five years of age.

In* Nautilus* the sexes are distinct in fact the male is larger than the female as it is provided with a large organ called spadix, which serves to introduce the sperm into the cavity of the female's coat. Reproduction therefore takes place by coupling. After which the female lays no more than ten large eggs (about 3 cm in diameter). The newborn babies have all the characteristics of the adult nautilus, that is to say they already have a perfectly developed shell inside which they live.

The octopus is one of their main predators as it is capable of piercing the shell and injecting a venom.

Note 2

STATE OF THE POPULATION

THE *Nautilus* they are fished both to be eaten and above all for their shells, much sought after by collectors or to make ornamental objects.

Unfortunately at present i* Nautilus* they are not protected by the Washington Convention on International Trade of Endangered Species (CITES), because there is not enough scientific information about them.

Indiscriminate fishing of them is made in various countries. Only Indonesia since 1987 has banned its trade while all the other countries around which nautilus usually swim allow hunting. Until all countries adopt a conservation policy, the best way to protect these amazing mollusks is by not purchasing their shells.

SOCIAL, ECONOMIC AND ECOSYSTEM IMPORTANCE

Unfortunately today i *Nautilus* they are illegally caught both for meat and for their shells.

They are also producers of so-called low prized pearls *coque de perle*.

CURIOSITY'

The name *nàutilos* comes from the Greek ναυτίλος which means "navigator".

Nautilus is the name of the first submarine built by the American inventor Robert Fulton in 1801 and commissioned by Napoleon. It consisted of copper sheets with an iron structure, 6.5 m long and equipped with a control tower for observation.

Nautilus is also the name of the submarine commanded by Captain Nemo, in the novels of Jules Verne (Nantes, February 8, 1828 - Amiens, March 24, 1905)* Twenty thousand leagues under the sea* is* The mysterious island*.

Image of the nautilus as it appears from the 1954 Disney film *Twenty thousand leagues under the sea* (Note 3)

The USS Nautilus was the first nuclear-powered military submarine with an enriched uranium reactor and pressurized water built by the United States Navy in 1954 and was the first ship to reach the North Pole passing under the ice sheet.

The Italian Royal Navy established in 1910 a class of submarines (two examples) called Nautilus.

I think it is important to pause for a moment also on the spiral shape of the shell of the *Nautilus*. In fact, the spiral itself is a geometric figure that wraps around itself in infinite turns around a point and is a very represented structure in nature. In fact, we find it for example in the flowers of the sunflower, in the horns of different animals, in the motion of cyclones, in the DNA, in the galaxies (the Milky Way has the shape of a spiral), in the shells ... This spiral is also of great importance from a mathematical point of view because the growth of the shell occurs following a particular succession of numbers called* Fibonacci sequence* (Pisa, 1180-1250) which in practice is a succession of natural integers where each number (apart from the first two) is the result of the sum of the previous two (1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89 ...).

To explain with a simple example how it works, let's take a squared sheet and use the side of a square as the unit of measurement and proceeding clockwise, draw two contiguous squares of side 1, then a square of side 2, followed by a square of side 3, then of side 5, then of side 8 and so on ... We then join the vertices of these squares with an arc of circumference, obtaining the spiral structure of the *Nautilus*, that is to say a spiral, called *logarithmic spiral*, which describes its structure.In practice, the Fibonacci sequence follows a sort of logarithmic spiral, that is to say a curve that continues indefinitely both inwards and outwards without ever reaching an end or a beginning. Fibonacci numbers and are related to each other, a definite relationship is obtained *golden section*, considered as the universal law of harmony, the mathematical expression of the beauty of nature *Nautilus *ben represents it with its shell that develops in a perfect logarithmic spiral, therefore in perfect harmony.

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*Nautilus pompilius* - Attribution: Profberger (English Wikipedia). Image licensed under Creative Commons Attribution-Share Alike 3.0 Unported
- Attribution: WikiFred (en.wikipedia.org). Image licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license