Placoneis abiskoensis has linear valves, with subcapitate apices. Placoneis elginensis and P. paraelginensis have capitate apices (in larger specimens) and the distal raphe ends are unilaterally deflected. Placoneis placentula has wide (12-20 µm) elliptic valves, with acutely rounded apices. Placoneis symmetrica has rostrate to capitate apices, radiate striae throughout and a higher areola density (28 in 10 µm).

LM scalebar = 10 µm
Placoneis explanata LM2 Placoneis explanata LM3 Placoneis explanata LM6 Placoneis explanata LM8 Placoneis explanata LM10 Placoneis explanata LM13
Length Range
22.3-37.2 µm
Width Range
8.5-11.4 µm
Striae in 10 µm
10-12 at the valve center, 17-19 at the apices

Placoneis abiskoensis

(Hust.) Lange-Bert. and Metzeltin 1996

Placoneis abiskoensis LM4 Placoneis abiskoensis LM3 Placoneis abiskoensis LM2 Placoneis abiskoensis LM1
Length Range
33.3-46.0 µm
Width Range
8.4-11.1 µm
Striae in 10 µm

Also compare to

Placoneis paraelginensis

Lange-Bert. in U.Rumrich, Lange-Bert. and M.Rumrich

Placoneis placentula

(Ehrenb.) Heinzerl.

Placoneis symmetrica

(Hust.) Lange-Bert.

Placoneis elginensis

(W.Greg.) E.J.Cox

Placoneis paraelginensis

Lange-Bert. in Rumrich et al.