Phylum Chlorophyta; sub-phylum Chlorophyceae; Order Zygnematales
There are two groups of Desmids: the "Placoderm" and the "Saccoderm" Desmids.
Placoderm desmids have cells composed of two halves (semicells), often almost divided from each other by deep median incisions. The cells are symmetrical about 3 planes, and often bear elaborate ornamentation. Genera are Cosmarium, Cosmocladium, Euastrum, Micrasterias, Staurastrum, Staurodesmus, Xanthidium.
Saccoderm desmids are simple shapes, cylindrical or spindle-shaped, rarely with any median constriction. This group forms the family Mesotaeniaceae and includes the genera Cylindrocystis, Mesotaenium, Netrium, Roya, Spirotaenia, Tortitaenia, and, in the suborder Closteriinae, Closterium, Gonatozygon and Penium, and in the suborder Desmidiinae, Actinotaenium.
ILLUSTRATIONS:click on an image to enlarge: use the browser back button to return to this page
|Semicells simple shapes, undissected, but margins may be crenellated. Apical view elliptical.|
|Cosmarium cyclicum v. arcticum|
|Cosmarium ?depressum v. planctonicum|
colonial desmid in a spherical mucilage sheath; cells similar to Cosmarium, linked by threads of mucilage.
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