The alveolates are a major clade of unicellular eukaryotes of both autotrophic and heterotrophic members. Chemotrophs can be either autotrophic or heterotrophic. Most excavates are unicellular, heterotrophic flagellates. It can easily adapt between heterotrophic and autotrophic lifestyles. Unlike heterotrophic prokaryotes, cyanobacteria have internal membranes. Some sources divide the heterokonts into the autotrophic Ochrophyta and heterotrophic Bigyra and Pseudofungi. They exploit the autotrophic, heterotrophic or mixotrophic properties of "C. vulgaris". A similar event occurred with photosynthetic cyanobacteria entering large heterotrophic cells and becoming chloroplasts. Thrombolites are ancient forms of microbial communities that can be photosynthetic or heterotrophic. Mixotrophic dinoflagellates are photosynthetically active, but are also heterotrophic. Thus there is the element of synergism between phytoplankton and heterotrophic bacteria. Currently known "Shewanella" species are heterotrophic facultative anaerobes. Photoautotrophs evolved from heterotrophic bacteria by developing photosynthesis. Tholins could have been the first microbial food for heterotrophic microorganisms before autotrophy evolved. Protozoa may also live as mixotrophs, supplementing a heterotrophic diet with some form of autotrophy.