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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 substitute. [49] [50] [51] In Samoa, nautilus shells decorate the forehead band of a traditional headdress called tuiga. [52]
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 not a golden spiral. The shell exhibits countershading, being light on the bottom and dark on top. This ...
Many biological structures including the shells of mollusks. [14] In these cases, the reason may be construction from expanding similar shapes, as is the case for polygonal figures. Logarithmic spiral beaches can form as the result of wave refraction and diffraction by the coast. Half Moon Bay (California) is an example of such a type of beach ...
For example, a golden spiral can be approximated by first starting with a rectangle for which the ratio between its length and width is the golden ratio. This rectangle can then be partitioned into a square and a similar rectangle and this rectangle can then be split in the same way. After continuing this process for an arbitrary number of ...
A cross-section of a Nautilus pompilius shell, showing the large body chamber, shrinking camerae, concave septa, and septal necks (partial siphuncle supports) All nautiloids have a large external shell, divided into a narrowing chambered region (the phragmocone) and a broad, open body chamber occupied by the animal in life. The outer wall of ...
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For example, in the nautilus, a cephalopod mollusc, each chamber of its shell is an approximate copy of the next one, scaled by a constant factor and arranged in a logarithmic spiral. [51] Given a modern understanding of fractals, a growth spiral can be seen as a special case of self-similarity. [52]
According to Stephen Skinner, the study of sacred geometry has its roots in the study of nature, and the mathematical principles at work therein. [5] Many forms observed in nature can be related to geometry; for example, the chambered nautilus grows at a constant rate and so its shell forms a logarithmic spiral to accommodate that growth without changing shape.