This is a dinoflagellate armored with cellulosic thecal plates, which have the somewhat unusual property of lying beneath the cell membrane. The dinoflagellates are a large and diverse algal group with no shortage of interesting characteristics. For example, most do not have histones and keep their chromosomes condensed for almost the entire cell cycle. I do not invite them to parties because I have little patience for guests who shout “Spartan!” every time someone goes for the guacamole.
Photo from here.
