Either of two genera of cephalopods. The pearly, or chambered, nautilus (genus Nautilus) lives in the outermost chamber of its smooth, coiled, usually 36-chambered shell, about 10 in. (25 cm) in diameter. A connecting tube adjusts the gases in the chambers, allowing the shell to act as a float. Nautiluses search the ocean bottom for shrimp or other prey, which they capture with up to 94 small, suckerless, contractile tentacles. The paper nautilus (genus Argonauta) feeds on plankton near the surface of tropical and subtropical seas. The female resembles an octopus but has a thin, unchambered, coiled shell, 12–16 in. (30–40 cm) in diameter. The much smaller male has no shell.
Chambered nautilus (Nautilus)—Douglas Faulkner
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