Proterospongia is considered connecting link between protists and sponges/metazoa due to

Options

A. Colonial nature
B. Choanocyte type of individuals
C. Sponge - like nature
D. All the above.

Answer

### Step-by-Step Solution:

1. **Understanding Proterospongia**: Proterospongia is a type of unicellular protist classified under the kingdom Protista, specifically within the class of Choanoflagellates.

2. **Connection to Sponges**: Proterospongia is considered a connecting link between protists and sponges (metazoa) because it exhibits characteristics that are similar to the simplest animals, which belong to the phylum Porifera (sponges).

3. **Colonial Nature**: One of the key features of Proterospongia is its ability to form colonies. This characteristic is also observed in sponges, where individual cells work together in a colony.

4. **Cellular Structure Similarity**: Proterospongia possesses cell structures that resemble choanocytes, which are specialized cells found in sponges. Choanocytes are flagellated cells with a collar-like structure that help in feeding and water circulation within the sponge.

5. **Sponge-like Characteristics**: The presence of these choanocyte-like structures in Proterospongia gives it a sponge-like nature, reinforcing its role as a connecting link between unicellular protists and multicellular organisms like sponges.

6. **Conclusion**: Therefore, Proterospongia is considered a connecting link between protists and sponges due to its colonial nature, similarity in cellular structure to choanocytes, and overall sponge-like characteristics.

### Final Answer:
Proterospongia is considered a connecting link between protists and sponges due to its colonial nature, similarity to choanocytes, and sponge-like characteristics.