When a large number of unicellular flagellated algae form a colony covered by a gelatinous membrane, it is called a motile enveloped colony. A colony in which a certain number of motile cells are arranged in a certain pattern is called a synobium. Synobium algae are interconnected and their flagella are outwardly oriented. Each synobium can contain 4-50,000 algae. E.g. Eudorina, Pleodorina, Pandorina, Volvox etc.