Biology
A detail of the external apex of a valve of Nitzschia sigmoidea under the electron microscope, showing the curved end of the raphe slit and the rows of small pores through the silica wall.
Diatoms are photosynthetic organisms. Their chloroplasts often appear brownish because, in addition to green chlorophyll, they contain brown and yellow pigments. In Nitzschia sigmoidea there are two chloroplasts - one at each end of the long, s-shaped cells.
Like many diatoms, Nitzschia species are able to glide over surfaces by secreting mucilage. Large populations of these diatoms can form a golden-brown coating on rocks and sediments, and are often clearly visible on intertidal muds at low tide.