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Melosira varians has smaller and much more delicate valves with inconspicuous ornamentation.

LM scalebar = 10 µm
Melosira undulata LM4 Melosira undulata LM3 Melosira undulata LM1 Melosira undulata LM2 Melosira undulata LM5 Melosira undulata LM6 Melosira undulata LM7
Diameter
30-81 µm
Width Range
28-47 µm
Striae in 10 µm
12-16

Melosira varians

C.Agardh 1827

Melosira varians LM6 Melosira varians LM1 Melosira varians LM2 Melosira varians LM4 Melosira varians LM7 Melosira varians LM3
Diameter
6-30 µm
Width Range
5-15 µm