Explanation:

- Nerve cells: These cells have long extensions and a complex structure to transmit electrical signals, not an amoeboid shape.

- White blood cells: These cells are indeed amoeboid in shape and have a distinctive central nucleus. They move and engulf pathogens, offering immune protection.

- Guard cells: These are found in plants and help control gas exchange by altering the size of pores; they are not amoeboid-shaped.

- Red blood cells: They have a biconcave disc shape and lack a nucleus when mature, so they do not fit the description.