A dinoflagellate is a one-celled aquatic protist, found in both salt and fresh water. Dinoflagellates make up a large proportion of the plankton in the ocean, and are an important part of the life cycle in many aquatic environments. The creatures have been identified and studied since the 1700s, and have probably been around for millions of years, along with several other primitive organisms.
Like other protists, a dinoflagellate is difficult to classify because it possesses traits held by plants, animals, and fungi. There is also a great deal of diversity within the biological order Dinoflagellata, leading to varying lifestyles and morphologies for dinoflagellates. As a general rule, a dinoflagellate has a unique cellulose cell wall which forms a series of protective plates. It also has two unequally sized flagella, small arms which are used for locomotion. One flagellum, called the transverse flagellum, wraps around the body of the dinoflagellate, providing the bulk of propulsive energy, and the longitudinal flagellum trails behind, acting as a rudder.
The two flagella cause a dinoflagellate to appear to whirl through the water, inspiring the scientific name, which means “whirling whips.” Mobile dinoflagellates whirl through the water in search of energy, and often cluster in large amounts called blooms. In some cases, a bloom is unnoticeable and harmless, but in other instances, the dinoflagellates may contain or secrete toxins. This is the case with a red tide, a characteristic dinoflagellate bloom which turns the water slightly red. The toxins are absorbed by shellfish, which are unsafe to eat as a result of their contamination.
Approximately half of all dinoflagellates photosynthesize for their energy, while the other half form parasitic or symbiotic relationships with other animals. This is the case with dinoflagellates which inhabit coral reefs, for example. Some are bioluminescent, meaning that their bodies glow. A bloom of bioluminescent dinoflagellates can lead to the appearance of glowing or illuminated waves, as they emit light when they are disturbed. This bloom is generally harmless, and can be quite beautiful at night.
Depending on the species and the circumstances, a dinoflagellate can reproduce sexually or asexually. In many cases, a dinoflagellate simply splits to create offspring. In others, dinoflagellates will sometimes join forces, forming a multicellular organism which later splits into four in a process called meiosis. Scientific study has also revealed that dinoflagellates sometimes join forces in periods of stress or resource scarcity, bonding into a single stronger organism which splits once the crisis has passed.