nautilus


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nautilus

or

chambered nautilus,

cephalopodcephalopod
, member of the class Cephalopoda, the most highly organized group of mollusks (phylum Mollusca), and including the squids, octopuses, cuttlefish, and nautiluses. The class as a whole has become adapted for a free-swimming existence.
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 mollusk belonging to the sole surviving genus (Nautilus) of a subclass that flourished 200 million years ago, known as the nautiloids. The spirally coiled shell consists of a series of chambers; as the nautilus grows it secretes larger chambers, sealing off the old ones with thin septa. The animal lives in the largest and newest chamber, with a tubular elongation of the body, known as the siphuncle, extending through the septa to the apex of the shell. The siphuncle removes liquid from the chambers and replaces it with gas, giving the animal the buoyancy that permits it to swim (backwards except when feeding), which it accomplishes by ejecting water through a funnel.

The nautilus breathes by means of two pairs of gills; it feeds on crabs and other animals, which it catches with its long, slender tentacles (numbering more than 90) that encircle the mouth. There is a thickened area over the head, called the hood, that acts as a protective lid when the animal withdraws into the shell. The nautilus lives in deep water in the S Pacific and Indian oceans. It is active at night; during the day it stays hidden in coral crevices. It is hunted for its shell, which is used in jewelry and ornaments.

The paper nautiluspaper nautilus
or argonaut,
pelagic, surface-dwelling cephalopod mollusk of the genus Argonauta. Like the closely related octopus, the paper nautilus has a rounded body, eight tentacles, and no fins. It is so named for the beautiful papery shell, up to 8 in.
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, which is not a true nautilus, is a close relative of the octopus, belonging to the order Octopoda. The true nautilus is classified in the phylum MolluscaMollusca
, taxonomic name for the one of the largest phyla of invertebrate animals (Arthropoda is the largest) comprising more than 50,000 living mollusk species and about 35,000 fossil species dating back to the Cambrian period.
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, class Cephalopoda, order Nautilida, family Nautilidae.


Nautilus:

see submarinesubmarine,
naval craft capable of operating for an extended period of time underwater. Submarines are almost always warships, although a few are used for scientific, business, or other purposes (see also submersible).
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.

Nautilus

 

a genus of invertebrates of the superorder Nautiloidea and the class Cephalopoda.

Nautilus is now the only living group of the subclass Tetrabranchia. The shell is large (up to 30 cm in diameter) and external, spirally coiled in a single plane, and divided by partitions into a series of chambers. The body of the mollusk is located in the last and largest chamber. The chambers serve the animal as a hydrostatic apparatus. To descend, it fills them with water to varying degrees, while to rise it fills them with a gas with a high content of nitrogen. There are several species, which are found in the Indian Ocean and the western part of the Pacific. Nautilus crawls along the bottom (at shallow depths) or swims on the surface of the water. It feeds on small crabs and fish.

Nautilus

[′nȯd·ə·ləs]
(invertebrate zoology)
The only living genus of the molluscan subclass Nautiloidea, containing the only living cephalopods with an external chambered shell and numerous cephalic tentacles, six species live in the western Pacific and around the East Indies.

Nautilus

submarine in which its builder, Captain Nemo, cruises around the world. [Fr. Lit.: Jules Verne Twenty Thousand Leagues Under the Sea]

nautilus

1. any cephalopod mollusc of the genus Nautilus, esp the pearly nautilus
2. short for paper nautilus
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