Chaetoceros diadema is a diatom in the genus Chaetoceros. The easiest way to identify this species is by finding the very characteristic diadem-like resting spores.
Cells united into chains. Very characteristic, diadem - like spores (see species image). One chloroplast. Base of setae is short.
Chaetoceros constrictus is quite similar in the vegetative stage, but its resting spores are different from C. diadema resting spores .
^ Tomas, C. R., Hasle G. R., Syvertsen, E. E., Steidinger, K. A., Tangen, K., Throndsen, J., Heimdal, B. R., (1997). Identifying Marine Phytoplankton, Academic Press.