Micrasterias americana shows a very special morphological phenomenon. The four minor extensions of apical lobes are optional. But if some of them are formed they show rotational symmetry according to direction of the appendices. This depth of focus picture assembling 26 high resolution shots shows a specimen with all four extensions formed.
Sample from sphagnum pond situated in the northern alpine region of Austria near Salzburg. Images were taken using Zeiss Universal with Olympus C7070 CCD camera.
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Wolfgang Bettighofer, www.protisten.de.