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Ectocarpus shows haplodiplontic life cycle ,i.e. ectocarpus goes through a phase in which they are multicellular and haploid (the gametophyte), and a phase in which they are multicellular and diploid (the sporophyte),  whereas fucus has a diplontic life cycle .i.e. in diplontic life cycle,  the diploid stage is multicellular and haploid gametes are formed.

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