Statospores are endogenous cysts formed within the vegetative cell by members of Chrysophyceae such as Ochromonas spp. The cyst walls consist predominantly of silica and so are often preserved as fossils. These statospores are spherical or ellipsoidal, often ornamented with spines or other projections. The wall is pierced by a pore, sealed by an unsilicified bung, and within the cyst lie a nucleus, chloroplasts, and abundant reserve material. After a period of dormancy the cyst germinates and liberates its contents in the form of one to several flagellated cells.
Akinetes are of widespread occurrence in the blue-green and green algae. They are essentially enlarged vegetative cells that develop a thickened wall in response to limiting environmental nutrients or limiting light. Figure 1.18 shows the akinetes of Anabaena cylindrica (Cyanophyta). They are extremely resistant to drying and freezing and function as a long-term anaerobic storage of the genetic material of the species. Akinetes can remain in sediments for many years, enduring very harsh conditions, and remain viable to assure the continuance of the species. When suitable conditions for vegetative growth are restored, the akinete germinates into new vegetative cells.
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