Short, thick outgrowths that allow prokaryotes to attach to surfaces or each other are called pili.
Pili are small hair-like structures that enable some bacteria to attach and adhere easily to the cell surface. They are shorter and more numerous than bacterial flagella and are composed of a protein called pilin. There are two types of pili:
1. Sex pili-for the conjugation (the transfer of genetic material between bacteria)
2. Common pili-for the solid surface attachment.
