[DNA]

A day of discovery.
This is the first time I see on print why the dinos and cyano like to hang out together.
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Most dinoflagellates are encased in plates of armor.

Dinoflagellates are surrounded by a complex covering called the amphiesma, which consists of outer and inner continuous membranes, and between which lie a series of flattened vesicles. In armored forms, these vesicles contain the thecal plates, cellulose plates that are the "armor". This armor may be lacking (the cells are "naked"), and some species shed their theca under certain environmental conditions.

Armored dinoflagellates have two major plate regions composed of two to 100 individual plates. The edges of the plates overlap, sliding apart as the cell increases in size and allowing the cell to expand. The plates come in many varied shapes, from spherical forms like Peridinium to elongate horn-like forms such as Ceratium. In addition, some species have ridges or crests -- especially members of the Dinophysiales, such as the one shown at right. In some, the crests may be hollow and house cyanobacteria which provide fixed nitrogen to the host. This is most common in nitrogen-poor waters.

Source: http://www.ucmp.berkeley.edu/protista/dinoflagmm.html