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.

Cosmarium	Cosmocladium	Euastrum	Micrasterias	Staurastrum	Staurodesmus	Xanthidium
Saccoderm:	Closteriinae		Mesotaeniaceae		Desmidiinae

ILLUSTRATIONS:

Saccoderm: Closteriinae

Closteriiniae:Closterium	unicellular Desmid, varying from crescent shaped to straight: radius of curvature, dimensions and wall ornamentation distinguish species
	Closterium ?abruptum
	Closterium acerosum
	Closterium aciculare
	Closterium angustatum
	Closterium attenuatum
	Closterium baillyanum
	Closterium closterioides
	Closterium cornu
	Closterium costatum
	Closterium dianae
	Closterium dianae v. minus
	Closterium dianae v. pseudodianae
	Closterium directum
	Closterium ehrenbergii
	Closterium gracile
	Closterium gracillimum
	Closterium idiosporum
	Closterium incurvum
	Closterium intermedium
	Closterium jenneri
	Closterium juncidum
	?Closterium juncidum v. elongatum
	Closterium kutzingii
	Closterium lebleinii
	Closterium littorale
	Closterium lunula
	Closterium moniliferum
	Closterium navicula
	Closterium ? parvulum
	Closterium praelongum
	Closterium ralfsii
	Closterium setaceum
	Closterium striolatum
	Closterium venus
Closteriiniae: Gonatozygon	Filamentous Desmid: elongated cells usually in pairs joined end-to-end, ends slightly swollen, cell surface decorated, chloroplast axile.
	Gonatozygon kinahanii
	Gonatozygon monotaenium
Closteriiniae: Penium	Unicellular Placoderm Desmid: cylindrical with rounded ends, cell wall granular, 1 chloroplast in each semicell (sometimes interrupted in P. margaritaceum).
	Penium exiguum
	Penium margaritaceum
Desmidiinae (suborder) : Actinotaenium
	Actinotaenium curtum

Cosmarium	Cosmocladium	Euastrum	Micrasterias	Staurastrum	Staurodesmus	Xanthidium
Saccoderm:	Closteriinae		Mesotaeniaceae		Desmidiinae

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John Kinross