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Genus: Thalassiosira

Classification
General Close

Centric

(diatoms) Having radial symmetry, i.e., cell is shaped like a coin or a tuna can or a soup can.

Centric diatom
Description
Shape Cylindrical to coin-shaped
Size 2 - 186 μm (although most are < 80 μm)
Colour Yellow-brown
Connection Organic threads extending from central Close

Strutted process

(how is this different than marginal process?) In some diatoms, a narrow tube through the frustule that is usually associated with the secretion of chitin. It may appear as a marginal process or as a simple pore in the valve wall (Spaulding et al. 2010).

strutted process(es)
Covering Silica Close

Frustule

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

frustule
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Flagellum

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

Flagella		 None
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Chloroplast

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

Chloroplast		 Numerous, small, plate-like
Behaviour
Lifestyle Close

Photosynthesis

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.

Photosynthetic. Sexual/asexual. Close

Auxospore

In diatoms, the special cells that restore normal size following cell division. Auxospores are associated with sexual reproduction (Horner 2002).

Auxospores present
Harmful effects Known for some species
Distribution
Habitat Close

Neritic

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).

Neritic
Geographic Cold and temperate regions
Seasonal Often forms extensive spring and fall blooms
Growth Conditions
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Salinity

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).

Salinity		 18 - 38
Temperature -2 - 29°C
T. anguste/lineata T. nordenskioeldii/aestivalis/pacifica
T. punctigera T. rotula

Classification

Empire Eukaryota
Kingdom Chromista
Subkingdom Harosa
Infrakingdom Heterokonta
Phylum Ochrophyta
Subphylum Khakista
Class Coscinodiscophyceae
Subclass Coscinodiscophycidae
Order Thalassiosiranae
Family Thalassiosirales
Genus Thalassiosira Cleve 1873

(Guiry and Guiry 2011)

Lifestyle

Photosynthetic. Reproduces sexually and asexually. Large lobed auxospores are present, formed by separation of parent Close

Valve

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

valves (Cupp 1943).

Description

Cells are short and cylindrical to Close

Discoid

Disc-shaped.

discoid. Cells of most species are connected in flexible chains by organic threads extruded from central strutted process(es). Very few species live in groups covered in mucilage (not common around B.C.) or are solitary (T. punctigera). Strutted processes are also present on the valve Close

Margin

The outline or border that defines the shape of an organism or cell.

margins, and most species also have straight threads extending out from these Close

Process

A natural projection or appendage on an organism.

processes (Hasle and Syvertsen 1997). The valve face is covered in Close

Areola(e)

In diatoms, the regularly repeated hexagonal holes on the valve walls (HPP 2003).

areolae or Close

Punctum

(plural: puncta) A sharp tip or small point on any part of an organism's anatomy.

puncta. Chloroplasts are numerous, small and plate-like (Cupp 1943). Cells are yellow-brown in colour.

Measurements

Diameter: 2 - 186 μm (although most species are < 80 μm)
(Hasle and Syvertsen 1997)

Key to local species

Cells usually solitary; valves convex; few thick Close

Spine

In some diatoms, "closed or solid structures projecting from the cell wall;" in dinoflagellates, solid projections that usually taper to a point.

spines on valve margins T. punctigera
Cells connected by a single thin thread; cell edges usually bevelled;
valve centre usually concave T. nordenskioeldii/aestivalis/pacifica
Cells connected by a bundle of central threads (appears thick); cells widely discoid T. rotula
Cells connected by multiple subcentral threads T. anguste-lineata

Similar genera/species

Individual Thalassiosira species in valve view can be confused with Coscinodiscus species, which are usually much larger in size and do not have any organic threads extending from the cell.

Harmful effects

Known for some species (see species profiles).

Habitat

Neritic (Cupp 1943).

Distribution

Mainly found in cold and temperate regions (Cupp 1943) and often forms extensive blooms in spring and fall.

Environmental Ranges

Depth range (m): 0 - 3300
Temperature range (°C): -2.045 - 29.468
Nitrate (μmol L-1): 0.053 - 34.037
Salinity: 17.940 - 37.775
Oxygen (mL L-1): 3.946 - 9.192
Phosphate (μmol L-1): 0.046 - 2.366
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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).

Silicate (μmol L-1): 0.648 - 125.490
(OBIS 2012, cited in EOL 2012)

References

Cupp, E. E. 1943. Marine Plankton Diatoms of the West Coast of North America. University of California Press. Berkeley, California. 238.

Encyclopedia of Life (EOL). 2012. Thalassiosira. http://eol.org/pages/12082/overview. Accessed 19 Feb 2012.

Guiry, M. D. and Guiry, G. M. 2012. Thalassiosira Cleve, 1873: 6. http://www.algaebase.org/search/genus/detail/?genus_id=43768. Accessed 19 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.

Ocean Biogeographic Information System (OBIS). 2012. Thalassiosira. http://www.iobis.org/mapper/?taxon_id=518563. Accessed 19 Feb 2012.