Staurodesmus extensus

Staurodesmus extensus  is characterized by biradiate cells with an elongate isthmus. Semicells are rectangular to obversely trapeziform in outline and the apical angles are furnished with a spine. Length and projection of the spines are most variable (giving rise to the distinction of quite a series of varieties). In the Netherlands, Std. extensus is one of the most common Staurodesmus species to be encountered in  acidic habitats. Sexual stages (zygospores) can be met with occasionally.

Image © Henk Schulp

Staurodesmus extensus. Note the elongate isthmus and the obversely trapeziform semicells.

Cell dimensions (L x B): ca 30 x 35 µm (including spines).

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Another specimen of Std. extensus, marked by relatively long spines (cf var. joshuae).

Image © Henk Schulp

Zygospore of Std. extensus with adhering, empty gametangial cells. The globose spore is furnished with solid spines gradually broadening towards their base.

Image © Henk Schulp