They have a characteristic transverse flagellum that encircles the body in a groove referred to as the cingulum. They also possess a longitudinal flagellum perpendicular to the transverse flagellum. This gives them a distinctive spiral to their swimming motion. The cell wall of many dinoflagellates is divided into plates of cellulose. These plates form a distinctive geometry known as tabulation, which is the main means for classification.
Dinoflagellates form a major part of primary planktonic production in oceans.
Most dinoflagellates have a somewhat complex life cycle involving several steps, both sexual and asexual, motile and non-motile. Even though they are important producers and a key component to the food chain, dinoflagellates are also known for producing deadly toxins, especially when they are present in large numbers. They can not only kill a large range of marine species, but can also impart fatal toxins into several species, especially shellfish. Filter-feeding shellfish such as oysters, clams and mussels consume gynnodinium breve and concentrate the toxins in various organs. Usually deadly to finfish, shellfish are relatively unaffected.