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Heterosigma akashiwo syn Olisthodiscus carterae, Entomosigma akashiwo, Heterosigma carterae (photographed at 600x magnification)

Species is a member of the Rhahidophyceae family, along with Olisthodiscus and Chattonella, rather than a Chrysophyte. Small cells averaging 25u in diameter. Many golden brown chloroplasts.  Cell wall absent. Cells may appear in different shapes including spheroidal, ovoid, oblong and lumpy (resembling a cornflake). Sometimes forms extensive blooms in mid-summer to fall when water temperatures are greater than 15C. Toxic to fish. 
This sample was collected from the fish weir on Muddy Creek in late June of 2002. Cells numbered over 14,000 per milliliter. There was a larger than normal Menhaden die-off at that time, but no correlation could be made with existing information.

Another photo of this species as it appears in tropical waters can be seen by clicking