Dinoflagellate have 1 to 3 whiptails (flagellates), hence the name. That is about the only commonality among the 2,000 species.
Most dinoflagellates have an odd nucleus, called a dinokaryon, with chromosomes attached to the nuclear membrane. These chromosomes lack histones, and so stay condensed throughout interphase, which is strange.
Once considered a primitive prokaryotic holdover owing to their peculiar practice of genetic management, the chromosomal doings of dinokaryons are instead simply distinctive to other eukaryotic life.
Overall, dinoflagellates cover the food chain range: as autotrophs, heterotrophs (phagotrophs), symbionts (e.g., coral), and parasites.
A popular pastime for social dinoflagellates is to bloom into concentrations of more than a million per milliliter of water. Some produce neurotoxins and kill hapless fish. Others are innocuous. A few are flashy: bioluminescent blooms that blink when disturbed.
Hard times can make a dinoflagellate congregate for protection. 2 cells fuse, entering hibernation after tucking in extra fat, and forming a hard shell, sometimes even spikes.
When prospects return to promising, dormant dinoflagellates break out of their shells, separate, and start life anew. Ah, to be young again, with a new tail at the start of life’s tale.