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Narrow valves with protracted apices distinguish R. californica from R. abbreviata, which is wider and has bluntly rounded apices. The striae of R. abbreviata are lineate on both valves. In contrast, the striae of R. californica are lineate, except they are often punctate bordering the axial area. Rhoicosphenia californica is smaller than R. stoermeri. The striae of R. stoermeri are distinctly punctate.

LM scalebar = 10 µm
Rhoicosphenia californica LM1 Rhoicosphenia californica LM2 Rhoicosphenia californica LM3 Rhoicosphenia californica LM4 Rhoicosphenia californica LM5 Rhoicosphenia californica LM6 Rhoicosphenia californica LM7
Length Range
8-50 µm
Width Range
3-6 µm
Striae in 10 µm
11-12 in the center valve, 13-15 at the ends

Rhoicosphenia abbreviata

(C.Agardh) Lange-Bert. 1980

57002  Lm1 1 57002  Lm3 1 57002  Lm5 1 57002  Lm2 1 57002  Lm4 1
Length Range
10–55 µm
Width Range
4–8 µm
Striae in 10 µm
15-20

Rhoicosphenia stoermeri

Thomas and Kociolek 2015

Rhoicosphenia stoermeri LM7 Rhoicosphenia stoermeri LM6 Rhoicosphenia stoermeri LM5 Rhoicosphenia stoermeri LM4 Rhoicosphenia stoermeri LM3 Rhoicosphenia stoermeri LM2 Rhoicosphenia stoermeri LM1
Length Range
25-84 µm
Width Range
6-9 µm
Striae in 10 µm
11-13 in the center valve, 14-16 at the ends