Bacteria genital villi (eng. bacteriophage hair - phage tail) are thread-like structures on the shell of various bacteria that are capable of adsorbing on DNA- or RNA-containing phages.
Villi are formed in bacterial cells that contain plasmids, that is, genetic elements that are present inside the bacterial cell, but do not encode its own protein. Instead, they store information for protein synthesis that the bacterium can use when needed.