algae (AL-jee)
plural noun.

(singular: alga) diverse group of aquatic organisms, the largest of which are seaweeds.

blue-green algae (BLOO-GREEN AL-jee)
noun.

type of aquatic bacteria (not algae) that can photosynthesize light to create energy. Also called cyanobacteria and (in freshwater habitats) pond scum.

coralline algae KOR-uh-lahyn AL-jee
noun.

type of red algae with a calcareous skeleton.