Compare

Chaetoceros coloradensis, C. muelleri var. subsalsum, and C. transisetus grow as single cells.

LM scalebar = 10 µm
Chaetoceros muelleri LM7 Chaetoceros muelleri LM4 Chaetoceros muelleri LM6 Chaetoceros muelleri LM3 Chaetoceros muelleri LM2 Chaetoceros muelleri LM5 Chaetoceros muelleri LM1
Diameter
8.4-19.5 µm

Also compare to

Chaetoceros coloradensis

Li and Kociolek

Chaetoceros muelleri var. subsalsum

(Lemmerm.) J.R.Johans. and S.R.Rushforth

Chaetoceros transisetus

J.R.Johans. and Boyer