- any of numerous microscopic, unicellular, marine or freshwater algae of the phylum Chrysophyta, having cell walls containing silica.
- any microscopic unicellular alga of the phylum Bacillariophyta, occurring in marine or fresh water singly or in colonies, each cell having a cell wall made of two halves and impregnated with silicaSee also diatomite
1845, coined from Greek diatomos “cut in two,” from diatemnein “to cut through,” from dia- “through” (see dia-) + temnein “to cut” (see tome). So called because they typically appear to have been cut in half. Related: Diatomic.
- Any of various one-celled aquatic organisms of the class Bacillariophyceae that have hard bivalve shells (called frustules) composed mostly of silica, can perform photosynthesis, and often live in colonies. They make up a large portion of the marine plankton and are an important food source for many aquatic animals. The skeletal remains of diatoms are the main constituent of diatomite.