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:

Saccoderm:

Mesotaeniacea

Cylindrocystis


Unicellular Saccoderm Desmid: cells short, cylindrical with rounded ends, with 2 stellate chloroplasts
 

 

Mesotaenium


Saccoderm desmid with a single chloroplast
       
   
This example has 4 longitudinal ridges, which is not reported in FAFBI.
The cells were found in dense mucilage adhering to moss on a greenhouse roof

 

Netrium

 
Unicellular placoderm Desmid: cylindrical with tapering rounded ends, some slightly swollen in the middle, with 2 chloroplasts.
(N. interruptum has each chloroplast almost divided in 2)
 
 
Netrium digitus
 
Netrium interruptum
   

Roya

Saccoderm desmid: elongated cylindrical cell with rounded ends, usually slightly bent . The single chloroplast has a notch in the middle .
 
? Roya obtusa
(this example is rather shorter than usual)

Spirotaenia

Unicellular Placoderm desmid : cylindrical cell with rounded ends and spiral band chloroplast
 
 
 

Tortitaenia

Saccoderm desmid: cylindrical, tapering at both ends (spindle-shaped). Chloroplast with spiral ridges (cf. Spirotaenia)
 
Tortitaenia luetkemuelleri
   
Desmidiinae (suborder) : Actinotaenium
 
Actinotaenium curtum
   
   

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Saccoderm:      


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