DESMIDS

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.

             
Saccoderm:

ILLUSTRATIONS:

click on an image to enlarge: use the browser back button to return to this page

Placoderm

 


COSMARIUM

 

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  
 

 

COSMOCLADIUM

 

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

 
 
 
Cosmocladium saxonicum  
 
 

click on an image to enlarge: use the browser back button to return to this page

             
Saccoderm:

John Kinross
[return to desmid key]
(back to desmid key)
[CONTENTS]