Dinoflagellates are unicellular plankton that belong to the phylum dinoflagellata. They have a unique dinokaryotic nucleus and use photosynthesis to produce food. There are over 20,000 known species of dinoflagellates that live primarily in oceans, with some found in snow. While most are harmless, some cause harmful algal blooms that release toxins dangerous to sea life and humans. Dinoflagellates reproduce asexually through binary fission and have a distinctive top-like spinning motion enabled by their two flagella.