Although these organisms 
Although these organisms are officially eukaryotes, some scientists have labeled them "mesokaryotes" because of the unusual organization of their nuclei. Some of them occur in freshwater, but most live in warm seas. Most have stiff external cellulose plates resembling armor. After the male and female haploid cells fuse in reproduction, a cyst is formed that, when ruptured, begins dividing into daughter cells. For ten points, name this organism responsible for red tides.
Although these organisms are officially eukaryotes, some scientists have labeled them "mesokaryotes" because of the unusual organization of their nuclei.
{Dinoflagellate}