Isogamous condition with non-flagellated gametes is found in:
Fucus
Chlamydomonas
Spirogyra
Volvox
Sexual reproduction in algae takes place by three means.
Isogamous:- The fusion of two gametes either flagellated or non-flagellated that are similar in size. For eg; Chlamydomonas (flagellated), Spirogyra (non-flagellated).
Anisogamous:- Fusion of gametes that are dissimilar in size. For eg; some species of chlamydomonas.
Oogamous:- Fusion between one large non-motile female gamete with one small motile gamete. For eg; Fucus and Volvox.
Thus, the correct answer is option c.