(Conjugatophyceae) A class of the *Chlorophyta
whose members are distinguished by their distinctively symmetrical cells, anatomically complex plastids, and the lack of free-swimming forms. In addition, they reproduce by *conjugation
. It contains freshwater filamentous forms (e.g. Spirogyra, Zygnema) and unicellular forms, the desmids. The desmids are divided into the saccoderm desmids, commonly found in acidic pools and peat bogs, and the placoderm or true desmids, which are a major component of the phytoplankton. The cells of placoderm desmids are characteristically split into two virtually identical halves, joined by a narrow bridge at the centre. The cell wall is highly ornamented and indented.