Genus: Pseudo-nitzschia

General Close


(diatoms) A type of diatom that has longitudinal symmetry with valves that are linear or oval shaped. Some pennate diatoms possess a raphe, which allows them to be motile.

Shape Narrow and boat-shaped
Size Length 25 - 160 μm, width 0.5 -8 μm
Colour Yellow-brown
Connection Overlapping Close


In diatoms, the structurally distinct halves of the cell wall (Becker 1996).

Covering Silica Close


In diatoms, the hard and porous silica cell wall (Horner 2002).



(plural: flagella) A tail-like projection that sticks out from the cell body and enables movement.



An organelle in the cell that contains the cell pigments (Horner 2002). This is where photosynthesis occurs. A chloroplast is a specialized chromatophore.

Two, plate-like, one on each side of central plane
Lifestyle Close


The chemical process by which light energy, water and carbon dioxide are combined to produce oxygen and organic compounds. Photoautotrophic organisms (plants and algae) use this reaction to produce their own food.

. Sexual/asexual.
Harmful effects Most species produce Close

Domoic acid

(related to ASP) An amino acid produced by some species of diatoms. The neurotoxin responsible for amnesic shellfish poison (Jeffery et al. 2004).

domoic acid
, which can cause Close

Amnesic Shellfish Poison

(ASP, Pseudo-nitzschia) Mainly caused by domoic acid, a toxin produced by some diatoms. When shellfish consume phytoplankton, they can bioconcentrate the toxin leading to a potential health hazard for humans who consume the contaminated shellfish. Hazards may include gastrointestinal symptoms within 24 hours and/or neurologic symptoms within 48 hours of consumption of mussels (Jeffery et al. 2004).

Habitat Close


Describing shallow, near-shore areas and the organisms that live there. Refers to shallow marine waters ranging from the low tide mark to the continental shelf. Varying amounts of sunlight penetrate the water, allowing photosynthesis by both phytoplankton and bottom-dwelling organisms. Close proximity to land favours high nutrient content and biological activity (Encyclopedia Britannica 2011).

Geographic Close


Widely distributed; occurring in many parts in the world.

Seasonal Present from spring to fall in low to medium numbers
Growth Conditions


The dissolved ion content of a body of water. Can be measured in the following units: parts per thousand (PPT or ‰), practical salinity units (PSU), and absolute salinity (g/kg). PPT is measured by weight, denoting the number of parts salt per thousand total parts or a value of 10-3. PSU measures the conductivity of saltwater and compares it in a ratio to a standard KCl solution (because this is a ratio, salinity measured in this way can also be written without units). The newest unit of salinity is absolute salinity, which uses the mass fraction of salt in seawater (g salt per kg seawater) rather than its conductivity (TEOS-20 2010).

18 - 38
Temperature -2 - 29°C
P. delicatissima P. seriata


Empire Eukaryota
Kingdom Chromista
Subkingdom Harosa
Infrakingdom Heterokonta
Phylum Ochrophyta
Subphylum Khakista
Class Bacillariophyceae
Subclass Bacillariophycidae
Order Bacillariales
Family Bacillariaceae
Genus Pseudo-nitzschia Peragallo 1900

(Guiry and Guiry 2012)


Photosynthetic. Reproduces sexually and asexually.


Cells are narrow and Close


Torpedo-shaped. Shaped like a small boat when viewed from above.

, united in stepped chains with overlapping valve ends. Chains are motile. Two plate-like chloroplasts are located along the Close


In diatoms, the portion of the cell wall between the two valves of a cell; made up of intercalary bands (bands closest to the valves) and connecting bands (bands in the middle of the girdle). In dinoflagellates, the equivalent of a cingulum or transverse furrow (Horner 2002).

, one on each side of the median transapical plane. Cells are yellow-brown in colour (Hasle and Syvertsen 1997).
The valve face is covered with slits and pores (fibulae, Close


(referring to pores in diatoms) In diatoms, a striation or row of pores on the valve face. "In centric diatoms, striae may be radial, running from the centre of the valve to the margin ... In pennate diatoms, striae may be parallel to the median line of the valve or raphe" (Horner 2002).

, Close


(plural: interstriae) The non-perforated siliceous strip between striae (Hasle and Syvertsen 1996).

). The Close


"In some pennate diatoms, one or two longitudinal slits along the [long] axis or around the valve margins" (Horner 2002). Secretion of mucilage allows a pennate diatom to attach itself to or glide on a substrate (Regents of the University of California 2006).

is off-center and not raised above the valve (Hasle and Syvertsen 1997).


Length Close


(axis, spine) The region of the apex or point. Refers to the most anterior point or region of the cell (HPP 2003).

axis): 25 - 160 μm
Width Close

Transapical axis

In diatoms, the longitudinal axis of the valve.

(transapical axis
): 0.5 - 8 μm
(Hasle and Syvertsen 1997)

Key to local species

Transapical axis wider than 3 μm. P. seriata complex (see P. pungens/australis)
Transapical axis narrower than 3 μm. P. delicatissima complex (see P. delicatissima)

Harmful effects

Most species are capable of producing domoic acid, a neurotoxin that causes ASP (amnesic shellfish poisoning; Hasle and Syvertsen 1997). The level of toxicity may be correlated with the amount of urea present, such as that from runoff (Howard et al. 2007). Toxin production may also increase under P, Si (but not N) limitation (Fehling et al. 2004).


Neritic (Hasle and Syvertsen 1997).


Cosmopolitan (Hasle and Syvertsen 1997). Present from spring to fall in low to medium numbers forming part of diatom-dominated communities. Sometimes blooms in the summer in the waters close to the western coast of Vancouver Island to California.

Environmental Ranges

Depth range (m): 0 - 3300
Temperature range (°C): -2.045 - 29.468
Nitrate (μmol L-1): 0.030 - 34.037
Salinity: 17.940 - 38.049
Oxygen (mL L-1): 3.756 - 9.116
Phosphate (μmol L-1): 0.046 - 2.366

Silicic acid

A general term to describe chemical compounds containing silicon, oxygen and hydrogen with a general formula of [SiOx(OH)4-2x]n. Diatoms polymerize silicic acid into biogenic silica to form their frustules (Azam and Chisholm 1976).

(μmol L-1): 0.648 - 116.089
(OBIS 2012, cited in EOL 2012)


Encyclopedia of Life (EOL). 2012. Pseudo-nitzschia. Accessed 18 Feb 2012.

Fehling, J., Davidson, K., Bolch, C. J. and Bates, S. S. 2004. Growth and domoic acid production by Pseudo-nitzschia seriata (Bacillariophyceae) under phosphate and silicate limitation. Journal of Phycology. 40: 674-683.

Guiry, M. D. and Guiry, G. M. 2012. Pseudo-nitzschia H. Peragallo in H. & M. Peragallo, 1900: 263, 298. Accessed 18 Feb 2012.

Hasle, G. R. and Syvertsen, E. E. 1997. Marine diatoms. In: Tomas, C. R. (ed.) Identifying Marine Phytoplankton. Academic Press, Inc., San Diego. 5-385.

Kraberg, A., Baumann, M. and Durselen, C. D. 2010. Coastal Phytoplankton: Photo Guide for Northern European Seas. Verlag Dr. Friedrich Pfeil, Munchen, Germany. 204.

Ocean Biogeographic Information System (OBIS). 2012. Pseudo-nitzschia. Accessed 18 Feb 2012.

Howard, M. D. A., Cochlan, W. P., Ladizinsky, N. and Kudela, R. M. 2007. Nitrogenous preference of toxigenic Pseudo-nitzschia australis (Bacillariophyceae) from field and laboratory experiments. Harmful Algae. 6: 206-217.

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