Chaetoceros didymus

General Close


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

Shape Elliptic cylinder
Size Large diameter 10 - 40 μm, length 6 - 30 μm
Colour Yellow-brown
Connection Crossing of adjacent Close


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

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, large, plate-like; one in each Close


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

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. Close

Resting spore

In diatoms, a cell that requires a dormancy period prior to germination and can survive for several years; usually developed to survive adverse conditions. They are commonly observed in centric but not pennate diatoms. The morphology of the spore may be similar or different from a vegetative cell; they usually have heavily silicified walls and are rich in storage products (Horner 2002).

Resting spores


A rapid increase or accumulation of algal populations in an aquatic system. This will likely involve one or a few dominant phytoplankton species. This follows seasonal patterns (i.e., spring, summer or fall bloom) with dominant species being those that are best adapted to the environmental conditions of that time period. Discolouration of the water may be observed because of the algae's pigmentation. Blooms are often green but may be yellow-brown or red depending on the species present.

Information not available
Harmful effects None known
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 Temperate to warm waters
Seasonal Late spring and late summer
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).

30 - 36
Temperature -1 - 29 °C


*Sometimes referred to as C. didymum (Guiry 2012).


Empire Eukaryota
Kingdom Chromista
Subkingdom Harosa
Infrakingdom Heterokonta
Phylum Ochrophyta
Subphylum Khakista
Class Bacillariophyceae
Subclass Coscinodiscophycidae
Order Chaetocerotales
Family Chaetocerotaceae
Genus Chaetoceros
Species C. didymus Ehrenberg 1845

(Guiry and Guiry 2012)


Photosynthetic. Reproduces sexually and asexually (Guiry 2012). Resting spores present (Cupp 1943).


Cells are connected in straight chains. In 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).

view, valves are concave with a distinct semi-circular protrusion in the centre, producing Close


"In some diatoms, the space between the valves of adjacent cells in chains" (Horner 2002).

that are constricted in the middle. Spines are thin and arise from the corners of the cell, crossing near or away from the cell (Cupp 1943). Two large, plate-like chloroplasts are present, one in each valve, with a Close


Any of various protein granules that can be found in the chloroplast of some algae species. It is associated with the production of starch.

in the protrusion (Kraberg et al. 2010).
Internal spines diverge at 25 - 45 degrees to the chain axis, while terminal spines are almost parallel to the chain axis. Spines are rectangular in cross-section, covered in pores, and have small hairs near the base. The Close

Labiate process

In diatoms, a simple slit in the valve wall with two internal lips, one on each side of the slit. They can be useful in identification because they are positioned differently in different species (Horner 2002).

labiate process
is located in the centre (Kraberg et al. 2010).
Resting spores are smooth and paired, with short and thick spines, and are formed within mother cells that do not possess protrusions (Cupp 1943).


Large diameter Close


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

axis): 10 - 40 μm
Length Close

Pervalvar axis

The axis through the centre point of the two valves of a frustule. This axis is perpendicular to the valve face.

(pervalvar axis
): 6 - 30 μm
(Hasle and Syvertsen 1997, Kraberg et al. 2010)

Similar species


Harmful effects

None known.


Neritic (Cupp 1943).


Temperate to warm waters (Hasle and Syvertsen 1997).
Present throughout the year but with higher abundances in summer and fall in Northern European seas (Kraberg et al. 2010). Abundant during the summer off SW Spain (Establier et al. 1986).
Most abundant in late spring and late summer in Saanich Inlet (McQuoid and Hobson 1995). A common and abundant species off California (Cupp 1943).

Growth conditions

May be favoured by 12 - 16 °C temperatures and 15 - 16 h Close


The amount of time in a day that an organism is exposed to daylight. This varies between seasons, with photoperiods being longer in the summer and shorter in the winter.

(McQuoid and Hobson 1995). N-limited conditions may trigger the formation of resting spores, and extended periods of darkness may contribute further to their development (Itakura et al. 1993). May be favoured by conditions of high N:P ratio (> 80; Yoshida et al. 1998).

Environmental Ranges

Depth range (m): 0 - 300
Temperature range (°C): -1.462 - 29.468
Nitrate (μmol L-1): 0.056 - 34.037
Salinity: 30.119 - 35.801
Oxygen (mL L-1): 4.139 - 8.095
Phosphate (μmol L-1): 0.061 - 2.358

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): 0.754 - 92.735
(OBIS 2012, cited in EOL 2012)

Bloom characteristics

Information not available.


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. Chaetoceros didymum. Accessed 28 Mar 2012.

Establier, R., Lubian, L. M. and Balsco, J. 1986. Phytoplankton and hydrography on the Bay of Cadiz (SW Spain) from March 1980 to December 1983. Investigación Pesquera (Barcelona). 50(1): 69-81.

Guiry, M. D. 2012. Chaetoceros didymus Ehrenberg, 1845. Accessed 28 Mar 2012.

Guiry, M. D. and Guiry, G. M. 2012. Chaetoceros didymus Ehrenberg. Accessed 28 Mar 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.

Itakura, S., Yamaguchi, M. and Imai, I. 1993. Resting spore formation and germination of Chaetoceros didymus var. protuberans (Bacillariophyceae) in clonal culture. Nippon Suisan Gakkaishi. 59(5): 807-813.

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

McQuoid, M. R. and Hobson, L. A. 1995. Importance of resting stages in diatom seasonal succession. Journal of Phycology. 31(1): 44-50.

Ocean Biogeographic Information System (OBIS). 2012. Chaetoceros didymus. Accessed 28 Mar 2012.

Yoshida, Y., Mishima, Y. and Sato, M. 1998. Relationships between the dominant phytoplankton and DIN:DIP ratios in the inner part of Tokyo Bay. Nippon Suisan Gakkaishi. 64(2): 259-263.

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