Placoneis gastrum, P. placentula, P. minor, and P. clementis are similar in shape: elliptic valves with rostrate apices. Placoneis gastrum is distinguished by low stria density, broadly apices and large variable central area. Placoneis minor and P. clementis are shorter in length. Placoneis placentula has protracted, acute apices.

LM scalebar = 10 µm
Placoneis gastrum LM6 Placoneis gastrum LM5 Placoneis gastrum LM4 Placoneis gastrum LM3 Placoneis gastrum LM2 Placoneis gastrum LM1
Length Range
30.2-55.8 µm
Width Range
15.9-20.0 µm
Striae in 10 µm
7-9 near the center, up to 10 near the apices

Also compare to

Placoneis placentula

(Ehrenb.) Mereschk.

Placoneis clementis

(Grunow) E.J.Cox

Placoneis minor

(Grunow) Lange-Bert. in Metzeltin et al.