The Nautilus (from the Latin form of the original Ancient Greek, meaning, ‘sailor’) is a pelagic marine mollusk characterized by shells that are generally smooth, with compressed or depressed whorl sections, straight to sinuous sutures, and a tubular, generally central siphuncle. Having survived relatively unchanged for millions of years, nautiluses are often considered “living fossils.” Nautiluses are the sole living cephalopods whose bony body structure is externalized as a shell. The animal can withdraw completely into its shell and close the opening with a leathery hood formed from two specially folded tentacles. The innermost portion of the shell is a pearlescent blue-gray. The osmeña pearl, contrarily to its name, is not a pearl, but a jewelry product derived from this part of the shell. The nautilus shell presents one of the finest natural examples of a logarithmic spiral, although it is not a golden spiral. The use of nautilus shells in art and literature is covered at nautilus shell. Nautilus shells were popular items in the Renaissance cabinet of curiosities and were often mounted by goldsmiths on a thin stem to make extravagant nautilus shell cups. Small natural history collections were common in 19th-century Victorian homes, and chambered nautilus shells were popular decorations.