A deposit of calcium salts made in the stomach of many crustaceans during the period between molts. It may be used to store calcium needed in the new exoskeleton A sea slug of the Class Gastropoda, Phylum Mollusca.

Literally “stomach stones,” refers to stones ingested by a vertebrate to use for either digestion or ballast. The fossil equivalent of this is a trace fossil.

A stone that has been swallowed by an animal - usually a dinosaur - and used as part of the digestive system. Large herbivorous dinosaurs seem to have had a crop and gizzard, much like birds, and swallowed stones to put into the gizzard. These stones helped them to crush and grind the vegetation they ate more efficiently. When the dinosaur died, the stones in its gizzard would be left by the body as it decayed and can sometimes be found near - or even in - fossils. They are generally shiny, smoothed and have tiny pits in the surface where stomach acids has eaten away at them.

See Crab's eyes, under Crab.