equiangular

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Chambered nautilus (Nautilus pompilius)

The chambered 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 is to help avoid predators, because when seen from above, it blends in with the darkness of the sea, and when seen from below, it blends in with the light coming from above. The species has about 90 tentacles with no suckers. The oldest fossils of the species are known from Early Pleistocene sediments deposited off the coast of Luzon in the Philippines. Its diet consists of small crustaceans, carrion and small fish.

photo credits: montereybayaquairum, Ingrid Taylaraqua