(c) : Ulothrix is a green filamentous alga, belonging to Class Chlorophyceae. The plant body is an unbranched filament consisting of numerous cylindrical cells joined end and end. Under favourable conditions, each cell produces zoospores except holdfast. These zoospores are of two types macrozoospores and microzoospores. The macrozoospores are larger in size and are quadriflagellate and the microzoospores are smaller zoospores which may be biflagellate or quadrifagelleate. Under unfavourable conditions, nonmotile mitospores called aplanospores are produced. Sexual reproduction in Ulothrix is of isogamous type. The isogametes fuse to form a quadriflagellate zygospore which after meiosis forms 16 aplanospores or zoospores.