Answer:
Some of the diatoms are able to stay afloat and some of them lies at the bottom of the water bodies.
The can easily float because they have a large surface area and they can extend their body parts and makes them sink much slower.
Other types of the diatoms remains attached to the benthos and because they do not have appendages and they sink in the bottom of water.
Some of the diatoms that live on mud have the appendages for crawling.