Cyanobacteria ("blue-green algae")

Anabaena (note that each coil is made of multiple cells joined like pearls on a necklace; some coils are stained red, some green)

Anabaena (note the coil is made of numerous spherical cells, with an occasional heterocyst in the chain)

Anabaena (note occasional heterocysts in chain)

Nostoc 

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