Staurodesmus pterosporus, zygospore of triradiate formImage © Koos Meesters

Zygospore of Staurodesmus pterosporus (triradiate cell form). Notice rectangular spore with transparent 'wings' extending into the empty gametangial cells (basically, we have to do with remaining parts of the contents of the conjugating cells that do not participate in the formation of the actual spore).

Dimensions of rectangular spore: ca 20 x 15 µm

 

 

Desmid of the month
August 2014

Staurodesmus pterosporus

Vegetative cells of Staurodesmus pterosporus very much resemble those of Std. omearae but there is a big difference in zygospore morphology. Whereas zygospores in Std. omearae are globose and furnished with numerous, rather long spines (as in most Staurodesmus species) those in Std. pterosporus are most peculiar, i.e., flattened rectangular with produced angles following the outline of the enveloping, empty gametangial cells. By this, the spores in question make a somewhat winged impression (pteron = wing, feather). Unfortunately, zygospores are but incidentally encountered. Vegetative cells of this species often may be distinguished from those of Std. omearae in that the spines at the semicell angles are somewhat shorter and the transition from semicell body to spine is more abrupt.

Staurodesmus pterosporus, conjugating cells Image © Koos Meesters

Conjugating cells of Std. pterosporus (triradiate gametangial cells).

Staurodesmus pterosporus, biradiate vegetative cell Image © Koos Meesters

Biradiate vegetative cell of Std. pterosporus. Notice the rather abrupt attenuation of the apical angles of the semicell body into the (fairly short) spines.

Staurodesmus pterosporus, zygospore of biradiate form Image © Koos Meesters

Zygospore of Std. pterosporus (biradiate gametangial cells).