Chrysophyta, phylum (division) of unicellular marine or freshwater organisms of the kingdom Protista consisting of the diatoms (class Bacillariophyceae), the golden, or golden-brown, algae (class Chrysophyceae), and the yellow-green algae (class Xanthophyceae). In many chrysophytes the cell walls are composed of cellulose with large quantities of silica. Some have one or two flagella, which can be similar or dissimilar. A few species are ameboid forms with no cell walls. The food storage products of chrysophytes are oils or the polysaccharide laminarin. Formerly classified as plants, the chrysophytes contain the photosynthetic pigments chlorophyll a and c; all but the yellow-green algae also contain the carotenoid pigment fucoxanthin. Under some circumstances diatoms will reproduce sexually, but the usual form of reproduction is cell division. The diatoms and golden-brown algae are of great importance as components of the plankton and nanoplankton that form the foundation of the marine food chain.