Smallest sized prokaryote is ...................

Explanation

**Step-by-Step Solution:**

1. **Understanding Prokaryotes**: Prokaryotes are single-celled organisms that lack a nucleus and other membrane-bound organelles. They are generally smaller than eukaryotic cells.

2. **Identifying Size Range**: The size of prokaryotic cells typically ranges from about 0.5 micrometers to several micrometers.

3. **Researching Smallest Prokaryote**: Among prokaryotes, various species exist, but we need to identify the smallest one.

...