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|Size Range:||32.3-35 μm wide x 155.8-165 μm long (LUMCON Guide); 13-25 μm wide x 50-250 μm long (Cupp 1943); 28-75 μm wide x 90-600 μm long (Tomas 1997); sizes depend upon species|
|Key Characteristics:||Valves sigmoid, though sometimes only very slightly; two or four ribbon-like chloroplasts that follow a convoluted but orderly pattern from pole to pole or pole to center; rarely with many small round chloroplasts; striae are oblique and transverse but these are not always visible with light microscopy|
|Confused With:||Gyrosigma spp., which also have sigmoid valves, but have two large plate like chloroplasts, one against each side of the girdle; also Gyrosigma spp. have striae that are longitudinal and transverse but these are not always visible with light microscopy|