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.