Ordovician to Recent.  Virtually all marine, Bryozoans are exclusively colonial.  They share superficial similarities to corals but can be distinguished from corals in that the individual zooids (critters) are nearly microscopic (pinhole size or less) in size.  They are most closely related to worms and brachiopods.  The most common colony shapes are incrustations (coatings) and branched forms.

 
 
 
 

Along with corals they were important components of Paleozoic reefs.  One distinctive genus, Archimedes, (large picture) is the remains of the central stem of a spiral fan colony.

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