In which of the following sexual reproduction is of oogamous type and accompanied by complex post-fertilization developments ?

Options

A. Ulothrix
B. Spirogyrs
C. Polysiphonia
D. Ectocarpus

Answer

To determine which of the given options represents sexual reproduction of the oogamous type accompanied by complex post-fertilization developments, we need to analyze each option based on their reproductive strategies.

### Step-by-Step Solution:

1. **Understanding Oogamous Reproduction**:
- Oogamous reproduction involves the formation of two types of gametes: a large, non-motile female gamete (egg) and a smaller, motile male gamete (sperm). This type of reproduction is characteristic of many higher plants and some algae.

2. **Analyzing the Options**:
- **Eulothrix**: This organism reproduces via isogamous reproduction, where the male and female gametes are similar in size and morphology. Therefore, it does not fit the criteria of oogamous reproduction.
- **Spirogyra**: Like Eulothrix, Spirogyra also reproduces isogamously. The gametes are similar in size and shape, thus it is not oogamous.
- **Polysiphonia**: This organism exhibits oogamous reproduction. In Polysiphonia, the male gamete is smaller and motile, while the female gamete is larger and non-motile. Additionally, Polysiphonia is known for its complex post-fertilization developments, which include the formation of a multicellular structure.
- **Ectocarpus**: This organism shows anisogamous reproduction, where the male and female gametes are dissimilar in size and structure. Therefore, it does not meet the criteria for oogamous reproduction.

3. **Conclusion**:
- Based on the analysis, the correct answer is **Polysiphonia**, as it is the only option that exhibits oogamous reproduction and is accompanied by complex post-fertilization developments.

### Final Answer:
**Polysiphonia**