In fresh water most diatoms are of the pennate type. In marine waters the variety of body shapes is much wider. This image shows the top view of a large Coscinodiscus , a marine species that can just be seen with the naked eye. Clearly visible is the punctured structure of the cell. The yellow-brown chloroplasts used for photosynthesis are also easy to see.
Diatoms are able to locomote.
The pennates are the best movers. You can see them gliding slowly in the direction of the length of the cell. With these they can move over a substrate.