Arcella reproduce asexually through a process called binary fission. Here's how it works:

1. Nuclear Division: The single nucleus inside the Arcella divides into two identical nuclei.

2. Cytoplasm Division: The cytoplasm of the Arcella then divides into two equal parts, with each part containing one of the newly formed nuclei.

3. Shell Formation: Each daughter cell forms a new shell around itself, which may be slightly smaller than the original shell.

4. Separation: The two daughter cells, each with its own nucleus and shell, separate from each other, resulting in two independent Arcella.

This process allows for rapid population growth in favorable conditions.