Identification

English

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H. akashiwo was in the period 1971- ca 1985 often misidentified as Olisthodiscus luteus. Heterosigma akashiwo is distinguished from Olisthodiscus by its only slightly flattened cells versus the very flattened cells of Olisthodiscus. Also Heterosigma cells rotate during swimming while Olisthodiscus does not.. Heterosigma differs from Chattonella in having fewer and larger chloroplasts. Cells are typically 10-20 um long. Cells of H. akashiwo are slightly longer than wide, measuring 11-25 micrometer in length. The newly described species H. minor is almost round and measures 7-12 micrometer in diameter. In fixed samples, H. akashiwo can be difficult to identify (see image below). It may be confused with other species whose cells contain several yellow or yellow-brown chloroplasts such as Pseudochattonella or naked stages of other silicoflagellates.

Larsen, J. & Moestrup, Ø. (1989). Guide to toxic and potentially toxic marine algae.The Fish Inspection Service, Ministry of Fisheries, June 1989, 61 pp.  

Engesmo, A.; Eikrem, W.; Seoane, S.; Smith, K.; Edvardsen, B.; Hofgaard, A.; Tomas, C. R. (2016). New insights into the morphology and phylogeny of <i>Heterosigma kashiwo</i> (Raphidophyceae), with the description of <i>Heterosigma minor</i> sp. nov. <em>Phycologia.</em> 55(3): 279-294.