Akinete

Resting spores of cyanobacteria in order to survive through periods of cold (including freeze thaw) weather, desiccation and darkness (lack of photosynthesis).
Have thick cell walls like heterocysts to protect the internals.
The development of akinetes can be triggered by many factors. (E.g. desiccation, lack of carbon or nitrogen sources, light avalibility or temperature).

Akinetes have little resistance to heat (this is unlike bacterial endospores).
Akinetes have been shown to survive for 5 years in a desiccator (darkness, -20C and desiccation) and then go on to germinate normally.
Vegetative cells would only last a maximum of 2 week sin these conditions.
Viable akinetes have been found in sediments 64 years old.