Compare

Fragilariforma hungarica var. tumida has more narrowly tapered apices and only a single undulation along the valve outline. Fragilariforma constricta var. trinodis has narrow valves and relatively similar sized undulations. Fragilariforma horstii is much smaller, has a higher stria density and more narrow apices.

LM scalebar = 10 µm
Fragilariforma polygonata LM3 Fragilariforma polygonata LM2 Fragilariforma polygonata LM1 Fragilariforma polygonata LM5 Fragilariforma polygonata LM4
Length Range
22.1-30.2 µm
Width Range
9.8-10.5 µm
Striae in 10 µm
19-20

Fragilariforma horstii

E.Morales, Manoylov and L.L.Bahls 2012

Fragilariforma horstii LM1 Fragilariforma horstii LM2 Fragilariforma horstii LM3 Fragilariforma horstii LM4 Fragilariforma horstii LM5 Fragilariforma horstii LM6 Fragilariforma horstii LM7
Length Range
6.3-19.9 µm
Width Range
6.1-11.7 µm
Striae in 10 µm
34 in center to 40 ends

Also compare to

Fragilariforma hungarica var. tumida

(A.Cleve) Hamilton

Fragilariforma constricta var. trinodis

(Hust.) Hamilton