Bacteria that form a cluster of spheres are called staphylococci. The prefix "staphylo-" means "cluster of grapes," referring to the grape-like appearance of these bacteria when viewed under a microscope.

Examples of staphylococcal bacteria include:

* Staphylococcus aureus: This is a common bacterium that can cause a variety of infections, including skin infections, pneumonia, and food poisoning.

* Staphylococcus epidermidis: This bacterium is typically found on the skin and is usually harmless. However, it can cause infections in people with weakened immune systems.

* Staphylococcus saprophyticus: This bacterium can cause urinary tract infections in women.

Note: Not all spherical bacteria form clusters. Some spherical bacteria form chains (streptococci) or exist as individual cells.