Correct option (d) Spirogyra
Explanation:
Isogamy with non-flagellated gametes is seen it Spirogyra. it can reproduce both by sexual and asexual (vegetative) means.
They reproduce sexually by conjugation in which two non-flagellated morphologically similar but physiologically different gametes (isochronous) fuse together. One filament acts as male gamete and passes through the conjugation tube of another filament which acts as female gamete.
