The short extensions of the cell wall shown in the picture are called

Pili

Since here we are talking about bacterial cell, it contains two kinds of extension commonly- Short : pili; Long : Flagella

Flagella helps in movement of the bacterial cell, whereas pili helps in attachment of the cell to the surfaces. The number of flagella and pili are also different. Pili covers the entire surface of the bacterial cell and they are very thin and short in length.