Pheromones are used from basic unicellular prokaryotes to complex multicellular eukaryotes. Streptophyte algae are either unicellular or form multicellular filaments, branched or unbranched. Green algae are photosynthetic unicellular and multicellular protists that are related to land plants. Marine bacteriophages are significant parasites of unicellular marine cyanobacteria. Molecular signaling can occur between different organisms, whether unicellular or multicellular. Plant hairs may be unicellular or multicellular, branched or unbranched. All living organisms, whether unicellular or multicellular, exhibit homeostasis. Of eukaryotic groups, the protists are most commonly unicellular and microscopic. Most excavates are unicellular, heterotrophic flagellates. Most unicellular organisms are classed as microorganisms. It is found predominantly in protists and in unicellular algae. The Rhizaria are a species-rich supergroup of mostly unicellular eukaryotes. Diatoms form a (disputed) phylum containing about 100,000 recognised species of mainly unicellular algae. As predators, they prey upon unicellular or filamentous algae, bacteria, and microfungi. A single mitochondrion is often found in unicellular organisms.