any of a class (Bacillariophyceae) of microscopic algae (division Chromophycota), one-celled or in colonies, whose cell walls consist of interlocking parts and valves and contain silica: diatoms are a source of food for all kinds of marine life
Any of various microscopic one-celled or colonial algae of the class Bacillariophyceae, having cell walls of silica consisting of two interlocking symmetrical valves.