Light micrograph showing Prymnesium parvum, a phytoflagellate (Haptophyta) from marine brackish plankton; the nucleus is attached to the flagellar and haptonematal bases and can be seen between the chloroplasts. The species is of concern because of its ability to produce a toxin, prymnesin, which kills fish but appears to have little effect on humans. Magnification: 2500X at 4.5 x 5" print size.