To solve this problem, we need to identify which organism has flagellated male gametes.$\newline$Let's analyze each option:$\newline$• Option 1: Polysiphonia - This is a red alga, and its male gametes (spermatia) are non-motile.$\newline$• Option 2: Anabaena - This is a cyanobacterium, and it reproduces asexually. It does not have flagellated gametes.$\newline$• Option 3: Ectocarpus - This is a brown alga, and its male gametes are flagellated.$\newline$• Option 4: Spirogyra - This is a green alga, and it reproduces through conjugation, not using flagellated gametes.$\newline$Therefore, the correct answer is Option 3: Ectocarpus, as it has flagellated male gametes.