Male gametes are flagellated in Ectocarpus belonging to Phaeophyceae. The flagella of male gamete plays an important role in establishing initial sexual contact with the female gamete. However in Ectocarpus the female gamete too, is flagellated but is different in structure

Male gametes, also known as sperm cells, are flagellated in the organism Ectocarpus.

Ectocarpus is a type of brown algae that belongs to the class Phaeophyceae. It is a multicellular organism that exhibits a complex life cycle involving both sexual and asexual reproduction. The male and female reproductive structures in Ectocarpus are called gametangia.

Ectocarpus reproduces sexually by the fusion of male and female gametes. The male gametes, or sperm cells, are flagellated, meaning they possess a whip-like tail called a flagellum that allows them to move and swim towards the female gametes. The flagellum is a specialized structure that provides motility to the sperm and helps them reach the egg for fertilization.

The flagellated nature of male gametes in Ectocarpus is an adaptation that ensures efficient and effective fertilization. The flagellum propels the sperm through the water, increasing their chances of encountering and fertilizing the stationary female gametes. This mode of sexual reproduction allows for genetic variation and the production of offspring with diverse traits.

It is important to note that the other options listed in the question (Spirogyra, Polysiphonia, and Anabaena) do not belong to the same group as Ectocarpus and do not possess flagellated male gametes. Spirogyra is a filamentous green algae, Polysiphonia is a red algae, and Anabaena is a cyanobacterium. Each of these organisms has different modes of reproduction that may involve non-flagellated male gametes or other mechanisms for achieving fertilization.

In conclusion, the correct answer is option D: Ectocarpus. Male gametes in Ectocarpus are flagellated, which allows them to swim and reach the female gametes for fertilization.