Pennate diatoms. The cells are enclosed in siliceous valves. There are typically two valves - a top one and a lower one, and they are joined together with fine bands or girdle strips. With plastids containing chlorophylls a and c (they are stramenopiles after all). Genera and species distinguished largely by the shape of the organism and the pattern of pores and sculptings of the siliceous shell or frustule. Pennate diatoms are usually regarded as boat shaped, although some of the boats have very odd shapes. They can usually glide. This particular form is very common in sediments - the form apparently allowing the cell to penetrate through the pores of the sediments. Although enclosed in a siliceous shell, the shell of these rather delicate diatoms is flexible. The plastids contain chlorophylls a and c which gives the yellowy-brown colour. Differential interference contrast.