Other algal pigments such as chlorophylls and carotenoids are insoluble in water but can be extracted with organic solvents such as acetone and alcohol. Algae are also distinguished by their cellular organization. Unicellular algal species occur as single, unattached cells that may or may not be motile. Filamentous algal species occur as chains of cells attached end to end. These filaments may be few to many cells long and many be unbranched or branched in various patterns.
Colonial algae occur as groups of cells attached to each other in a nonfilamentous manner.
For example, a colony may include several to many cells adhering to each other as a sphere, flat sheet, or other three-dimensional shape. The cells may be embedded in a common matrix of gelatin secreted from the cells or attached by thin strands of cytoplasm. All the cells of a colony are similar in structure and function and metabolically independent. Multicellular organization is not typical of protists but describes algae of more complex design than simple colonies. Multicellular species have cells of different kinds and functions and show significant interdependence.