shell, in zoology, hard outer covering secreted by an animal for protection. It is also called the test, crust, or carapace. The term usually refers to the calcareous shells of the many species of mollusk but is also applied to the exoskeleton of the crab and other crustaceans, to the bony covering of the turtle, and to the hard exterior of a bird's egg. People have made use of mollusk shells since early times as receptacles for food and water, as currency (see shell money), and for ornament. The scientific study of shells is called conchology.

See P. A. Morris, A Field Guide to the Shells (of the Atlantic coast, 1973; the Pacific, 1974); J. M. Eisenberg, A Collector's Guide to Seashells of the World (1980); The Audubon Society Field Guide to North American Shells (1981); S. D. Romashko, The Shell Book (1984); K. R. Wye, The Simon & Schuster Pocket Guide to Shells of the World (1989).

Artillery projectile, cartridge case, or shotgun cartridge. It originated in the 15th century as a container for metal or stone shot, dispersed when the container burst after leaving the gun. Explosive shells, in use by the 16th century, were hollow cast-iron balls filled with gunpowder and lit by a fuse. Until the 18th century, such shells were used only in high-angle fire (including mortars). In the 19th century, shells were adopted for direct-fire artillery, notably in the form of shrapnel. Modern artillery shells consist of a casing (usually steel), a propelling charge, and a bursting charge; the propelling charge is ignited by a primer at the base of the shell and the bursting charge by a fuse in the nose. In rifle, pistol, and machine-gun ammunition, the word usually signifies the brass casing that contains the propulsive charge. In shotgun ammunition, the shell is the entire cartridge, including shot, powder, primer, and case.

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Any of several species of marine clams (family Solenidae) common in intertidal sands and muds, particularly of temperate seas. Razor clams have narrow and elongated shells (shaped like straight razors) up to 8 in. (20 cm) long. A large active foot enables them to move rapidly up and down within their burrow and retreat quickly when disturbed. With their short siphons (tubes) they feed on particulate material in seawater. Some species can swim short distances by jetting water through their siphons.

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Shell may refer to

  • Animal shell, or exoskeleton, including those of molluscs, turtles, insects and crustaceans
  • Seashell, the shells of various marine animals, especially marine mollusks
  • Eggshell, the outer covering of a hard-shelled egg

Any more or less hollow surface covering, including:

In science and mathematics:

In computing

  • Shell (computing), a type of computer user interface (for example a Unix or a DOS shell)
  • Shell account, a personal account that gives a user access to a Unix shell on another machine, usually through SSH
  • Shell sort, a sorting algorithm

In business

In media and entertainment:

  • Shell Thropp, a character from the books Wicked and Son of a Witch
  • "Shells" (Angel), a 2004 episode of the television series Angel
  • The Shells, an American doo wop group
  • Big Shell, an offshore decontamination facility in the videogame Metal Gear Solid 2: Sons of Liberty

As a surname:

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