cephalopod

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cephalopod

(sĕf`ələpŏd'), member of the class Cephalopoda, the most highly organized group of mollusks (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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), and including the squidssquid,
carnivorous marine cephalopod mollusk. The squid is one of the most highly developed invertebrates, well adapted to its active, predatory life. The characteristic molluscan shell is reduced to a horny plate shaped like a quill pen and buried under the mantle.
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, octopusesoctopus,
cephalopod mollusk having no shell, eight muscular arms or tentacles, a pouch-shaped body, and two large, highly developed eyes. The prey (crabs, lobsters, and other shellfish) is seized by the sucker-bearing arms and pulled into the web of tissue at the base of the
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, cuttlefishcuttlefish,
common name applied to cephalopod mollusks that have 10 tentacles, or arms, 8 of which have muscular suction cups on their inner surface and 2 that are longer and can shoot out for grasping prey, and a reduced internal shell enbedded in the enveloping mantle.
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, and nautilusesnautilus
or chambered nautilus,
cephalopod mollusk belonging to the sole surviving genus (Nautilus) of a subclass that flourished 200 million years ago, known as the nautiloids.
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. The class as a whole has become adapted for a free-swimming existence. Cephalopods are able to move about rapidly, and most are aggressive carnivores. The part of the body that forms the foot in other mollusks is located anteriorly in cephalopods instead of ventrally. Part of the foot area surrounds the mouth and is modified into sucker-bearing tentacles, used to capture prey. The tentacles number 8 in octopuses, 10 in squids, and as many as 90 in nautiluses. The rest of the foot forms a muscular funnel, or siphon, which expels water from the mantle cavity, permitting cephalopods to move about by a kind of jet propulsion. Only one existing genus, the nautiluses, the sole survivors of an extinct group known as the nautiloids, possesses an external shell. In the squid and cuttlefish the shell has become internalized and reduced, and in the octopus it is completely absent. The cephalopod head is large and is equipped with prominent eyes that resemble those of vertebrate animals. The class Cephalopoda has a fossil record of 10,000 species, although only 600 exist today. The nautiloid group was dominant through Paleozoic times, and the ammonitesammonite
, one of a type of extinct marine cephalopod mollusk, related to the nautilus and resembling it in having an elaborately coiled and chambered shell. Unlike the interiors of nautilus shells, the chambers of ammonite shells display intricately shaped septa and sutures.
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 flourished in the Mesozoic era.

cephalopod

any marine mollusc of the class Cephalopoda., characterized by well-developed head and eyes and a ring of sucker-bearing tentacles. The group also includes the octopuses, squids, cuttlefish, and pearly nautilus