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argonaut,pelagic, surface-dwelling 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.
..... Click the link for more information. mollusk of the genus Argonauta. Like the closely related octopusoctopus,
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
..... Click the link for more information. , 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. (20 cm) long, that surrounds the female while she broods her eggs. This structure, actually a calcareous egg case, is secreted by the tips of the female's two greatly expanded dorsal tentacles prior to egg laying. After she deposits her eggs in the floating egg case, the female takes shelter in it herself; she is usually found with her head and tentacles protruding from the opening, but she retreats deeper inside if disturbed. Air trapped in the egg case is used by the female to maintain neutral buoyancy. The much smaller male, which lacks the modified dorsal tentacles, often shares the shell of a female. It was once believed that the paper nautilus used the expanded tentacles, extended from the shell, as a sail. The true nautilusnautilus
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.
..... Click the link for more information. (genus Nautilus) belongs to a different cephalopod order. The paper 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.
..... Click the link for more information. , class Cephalopoda, order Octopoda.