cyanobacteria
    n 1: predominantly photosynthetic prokaryotic organisms
         containing a blue pigment in addition to chlorophyll; occur
         singly or in colonies in diverse habitats; important as
         phytoplankton [syn: cyanobacteria, blue-green algae]

cyanobacterium \cyanobacterium\ pl. cyanobacteria
\cyanobacteria\ [from the pigment phycocyanin.]
   any of a group of photosynthetic autotrophic prokaryotic
   microorganisms possessing characteristics of both bacteria
   and plants. When classed as bacteria, they are assigned to
   the Cyanobacteria; when classed as plants, they are assigned
   to the Cyanophyta. They were earlier named blue-green
   algae, a term less used now in technical discussions. Since
   the chlorophyll within the cyanobacteria is diffused
   throughout the cell, rather than being contained in
   chloroplasts, they are no longer thought of as true plants.
   [PJC]

blue-green alga \blue"-green al"ga\ pl. blue"-green al"gae
   [from the color and resemblance to algae.]
   any of a group of photosynthetic microorganisms possessing
   characteristics of both bacteria and plants. When classed as
   bacteria, they are assigned to the Cyanobacteria; when
   classed as plants, they are assigned to the Cyanophyta. They
   are now known to be prokaryotic, and are usually called
   cyanobacteria in technical contexts. See cyanobacterium.
   [PJC]