Actinoptychus senarius

General Close


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

Shape Close



Size Diameter 20 - 150 μm
Colour Yellow-brown
Connection None
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.

Numerous, large
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 stage
may be present.


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).

. Close


The ecological zone at the bottom of a body of water.

, Close


Organisms that drift at the mercy of the currents.

. Freshwater to brackish.
Geographic Close


Widely distributed; occurring in many parts in the world.

Seasonal More abundant during spring and fall, and after strong water-mixing events.
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).

31 - 36
Temperature -1 - 29 °C


Actinoptychus undulatus J. W. Bailey ex Hustedt 1927 Close


A difference in type. In naming species, a heterotypic synonym is one that comes into being when a taxon becomes part of a different taxon. Compare to homotypic.

Actinoptychus undulatus (J. W. Bailey) Ralfs 1861 (heterotypic)
Actinocyclus undulatus Kützing 1844 (heterotypic)
Actinocyclus undulatus J. W. Bailey 1842 (heterotypic)
Actinocyclus senarius Ehrenberg 1838 Close


The original name for an organism. In botany, the original published nomenclature from which a new binomial nomenclature is derived for a particular group of organisms (Tindall 1999).

, Close


Expressing the same fundamental type or structure; may or may not be symmetrical (e.g., the two valves of a diatom, where they are the same shape and appearance, but one is bigger than the other). In naming species, a homotypic synonym is one that comes into being when a taxon gets a new name (without being added to an already existing taxon).

(Guiry and Guiry 2012)


Empire Eukaryota
Kingdom Chromista
Subkingdom Harosa
Infrakingdom Heterokonta
Phylum Ochrophyta
Subphylum Khakista
Class Coscinodiscophyceae
Subclass Coscinodiscophycidae
Order Coscinodiscales
Family Heliopeltaceae
Genus Actinoptychus
Species A. senarius (Ehrenberg) Ehrenberg 1843

(Guiry and Guiry 2012)


Photosynthetic. Reproduces sexually and asexually (Guiry 2012). Resting stage may be present (Ishii et al. 2009).


Cells are discoid and usually solitary, but sometimes in loose clusters (Horner 2002). The Close


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

surface is divided into six Close


(symmetry) Describing a shape that many axes of symmetry. That is, it does not have a left and right like humans do (bilateral symmetry), but can be divided into equal halves no matter where you place the axis. Some examples of radially symmetrical organisms include sea stars and centric diatoms like Thalassiosira.

sectors, alternately raised and depressed, and visible as undulations 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. The central area is smooth and hexagonal; the rest is strongly Close


Synonym: perforated. Describing a surface that has many holes. Often used to describe the valve surface of diatom frustules.

(Cupp 1943). Chloroplasts are numerous and large (Hasle and Syvertsen 1997). Cells are yellow-brown in colour (Guiry 2012).
Raised sectors each have an external tube of 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 processes
near their margins (Horner 2002); the valve margin has numerous small Close


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

(Cupp 1943). In raised sectors, Close


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

toward the outside of the cell [are arranged] in fairly regular parallel radial rows, toward the center [they are] irregular. Close


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

in more or less regular, crossing Close


At a slanted angle (i.e., not parallel or perpendicular).

lines. The depressed sectors usually don't present Close


A natural projection or appendage on an organism.

, and in place of areolae only weakly marked dots that are bound together by a network of delicate lines. Close


Marked with tiny coloured spots or depressions.

coarser, radial 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).

less striking, oblique rows stronger. Valve margin narrow, faintly striated" (Cupp 1943).


Diameter: 20 - 150 μm
Height 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
): 10 - 70 μm
Areolae: 4 - 7 in 10 μm
Puncta on raised sector: 16 - 18 in 10 μm
Puncta on depressed sector: 13 - 14 in 10 μm
(Cupp 1943, Hasle and Syvertsen 1997)

Similar species

Thalassiosira spp. and other disc-shaped species. A. senarius can be easily distinguished by the undulated surface.

Harmful effects

None known.


Neritic. Benthic and planktonic (Cupp 1943). Often found in freshwater to brackish environments (Essien et al. 2008).


Cosmopolitan (Hasle and Syvertsen 1997), sometimes abundant in cold to temperate coasts (Kraberg et al. 2010).
Present throughout the year but slightly more abundant in winter and fall in Northern European waters (Kraberg et al. 2010). Irregular blooms from fall to early spring in the northwest coastal zone of Portugal (Resende et al. 2007). Abundant during the summer (wet season) in a Nigerian Close


The area where a river meets the ocean. Often characterized by high sediments, high nutrient levels, salinity fluctuations and tidal mixing.

(Essien et al. 2008).
Present throughout the year, with higher abundances during spring and fall, and especially after strong water mixing events (e.g. storms).

Growth conditions

Information not available.

Environmental Ranges

Depth range (m): 0 - 470
Temperature range (°C): 0.657 - 29.468
Nitrate (μmol L-1): 0.056 - 32.386
Salinity: 31.144 - 36.252
Oxygen (mL L-1): 4.500 - 7.789
Phosphate (μmol L-1): 0.062 - 2.229

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): 1.191 - 90.016
(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. Actinoptychus senarius. Accessed 07 Jan 2012.

Essien, J. P., Antai, S. P. and Benson, N. U. 2008. Microalgae biodiversity and biomass status in Qua Iboe Estuary mangrove swamp, Nigeria. Aquatic Ecology. 42: 71-81.

Guiry, M. D. 2012. Actinoptychus senarius (Ehrenberg) Ehrenberg, 1843. Accessed 07 Jan 2012.

Guiry, M. D. and Guiry, G. M. 2012. Actinoptychus senarius (Ehrenberg) Ehrenberg. Accessed 07 Jan 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.

Horner, R. A. 2002. A Taxonomic Guide To Some Common Phytoplankton. Biopress Limited, Dorset Press, Dorchester, UK. 200.

Ishii, K., Ishikawa, A. and Imai, I. 2009. Marine diatoms emerged from in situ surface sediment in a temperate embayment. Phycologia. 48(4, suppl.): 48.

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. Actinoptychus senarius. Accessed 07 Jan 2012.

Resende, P., Azeitero, U. M., Gonçalves, F. and Pereira, M. J. 2007. Distribution and ecological preferences of diatoms and dinoflagellates in the west Iberian Coastal zone (North Portugal). Acta Oecologica. 32(2): 224-235.

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