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.



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Semicells simple shapes, undissected, but margins may be crenellated. Apical view elliptical.  
Cosmarium blyttii  
Cosmarium botrytis  
Cosmarium brebissonii  
Cosmarium contractum  
Cosmarium cyclicum v. arcticum  
Cosmarium depressum  
Cosmarium formulosum  
Cosmarium impressulum  
Cosmarium ?depressum v. planctonicum  
Cosmarium portianum  
    Cosmarium ?punctatulum  
Cosmarium ralfsii  
Cosmarium speciosum  
Cosmarium subcrenatum  




colonial desmid in a spherical mucilage sheath; cells similar to Cosmarium, linked by threads of mucilage. 

Cosmocladium saxonicum  

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John Kinross
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