Nautilus

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See Nautilus in Wikipedia, the free encyclopedia.

A nautilus (Greek meaning "sailor") is any various shelled cephalopod of either genus Nautilus, or Allonautilus. Unlike all other living cephalopods (among those with eyes, at least), the nautilus has a lensless "pinhole camera" eye.

The nautilus should not be confused with the paper nautilus, a genus of pelagic octopi of the genus Argonauta. Paper nautilus get their common name because of the shell-like eggcase the female secretes to house herself while she broods her eggs. Early naturalists mistakenly thought that this structure was the shell, and that the (female) paper nautilus used the enlarge, fan-like tips of her two dorsal tentacles as sails.

Unlike all other living cephalopods, nautili (plural) do not have planktonic larvae. After mating, the female lays a single egg within an eggcase at a time, which she deposits on the seafloor, presumedly in deeper portions of coral reefs. The egg then develops into a minature version of the adult, complete with chambered shell. It is suspected that the reason the nautilus survived the K-T extinction event while the ammonites did not was that the ammonites had a planktonic larval stage that depended on a diet of calcium-rich foraminifera prey, while the nautilus did not.

Nautili have an extensive fossil record and are among the most important Paleozoic index fossils. The term "nautiloid" is used to refer to extinct relatives of the genera Nautilus and Allonautilus.

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