Diatoms are generally considered to be non-motile, meaning they lack the ability to move independently. However, they do exhibit a few forms of movement:

* Sliding: Diatoms can slide along surfaces using raphe, a groove or slit in their frustule (cell wall). The raphe is lined with a mucus-like substance that allows them to glide over surfaces. This movement is primarily used for foraging for nutrients and avoiding unfavorable conditions.

* Passive movement: Diatoms can be moved by water currents. This is the most common form of movement for diatoms, especially in planktonic species.

* Internal movements: Some species have been observed to exhibit cytoplasmic streaming, a movement of their internal fluids that can sometimes cause a slight displacement of the diatom.

In summary: Diatoms are primarily non-motile organisms, but they exhibit limited movement through sliding, passive transport by currents, and internal streaming.