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Allelopathic Describing a condition where the growth of one organism is inhibited by the release of chemicals by another organism into the shared environment.

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).

Amoeboid (movement) A crawling-like movement exhibiting flexibility in form.

Amoeboid (shape) Exhibiting a jelly-like changeable form.

Anisogamous Sexual reproduction involving two dissimilar gametes, e.g. sperm and egg.

Annular Ring-shaped.

Anoxic Describing a condition where there is no available oxygen for primary production. Oxygen may be present in complexed forms that are not available for phytoplankton. A related term is hypoxia, where oxygen is present at very low concentrations.

Ansula(e) In Ditylum and related diatoms, ansulae are the "fringes" seen near the ends of each cell. In SEM, you can see that each ansula is split into two ribbon-like points. A "single element of the fringed marginal ridge of Ditylum, shaped as a ribbon longitudinally split in its medium part" (Hasle and Syvertsen 1996).

Antapical Referring to the most posterior point of a cell. The opposite of apical.

Anterior The front. The part of the cell in the direction of movement. Opposite of posterior (HPP 2003).

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

Aphotic Describes a zone in the water where light from the surface does not penetrate and primary production cannot take place (i.e., aphotic zone).

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

Apical pore complex In many armoured dinokont dinoflagellates, describes a small hole on the epitheca. May be positioned on a horn and can be oval, round, narrow, curved or even fishhook shaped (MSIP 2011). Useful in distinguishing between different Alexandrium species.

Apiculus (plural: apiculi) Short, sharp, but not stiff projections (Kuo 2006).

Aplanospore A thin-walled spore that relies on water currents for passive transport. It is produced by some phytoplankton (including Scenedesmus and Geminella species [phylum Chlorophyta]) as a means of asexual reproduction. Upon germination, it develops a new cell wall distinct from the parent cell. The production of aplanospores may be a hereditary feature or may be an adaptation to withstand unfavourable environmental conditions (Transeau 1916).

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

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

Areolation Often used to describe holes (areolae) on the valve surface of diatom frustules.

Athecate (dinoflagellates) Describes a cell without a theca, i.e., without cellulose walls (Hoppenrath and Saldarriaga 2010).

Autotroph/autotrophic An organism that can use inorganic materials for primary production of complex organic compounds by practicing photosynthesis or chemosynthesis. For example, plants are autotrophic organisms.

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


Basionym 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).

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

Binary fission A form of asexual reproduction where one cell divides into two identical cells. All prokaryotes and some eukaryotes reproduce in this manner. Compare with mitosis, where the nucleus must also divide, adding an extra step to the process.

Bioconcentrate (or bioaccumulate) The process by which a substance (e.g., heavy metals, organic pollutants) concentrates as it moves up the trophic levels, from primary producers to herbivores to carnivores. This occurs because an organism absorbs the substance at a rate greater than that at which the substance is lost.

Bloom 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.

Boreal Relating to the area immediately south of the Arctic.


Calcareous Describing the character (i.e., chalky) or chemical presence of calcium carbonate (CaCO3) as a component of phytoplankton cell covering.

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

Chemoautotrophic Describing organisms that create their own food using chemical energy. An example of this is the bacteria that live near hydrothermal vents. They are able to gain energy by oxidizing iron.

Chemosynthesis Counter to photosynthesis, the process of oxidizing inorganic molecules or methane as a source of energy (rather than sunlight) to convert inorganic carbon molecules and nutrients into organic matter. Chemoautotrophic algae use this reaction to produce the energy they need to live and grow.

Chitin A long-chain polymer that is a derivative of glucose. In some diatoms, it is excreted by the strutted process to maintain buoyancy in the phytoplankton (Spaulding et al. 2010). In Thalassiosira, chitinous threads connect the cells in chains (Horner 2002).

Chloromonad A member of the order Chloromonadida. Chloromonads are protists, have two flagella (one trailing, one extending forward) and have many disk-shaped chloroplasts (Encyclopedia Britannica 2011). Some species are principally responsible for farmed salmon kills since 1986. Large blooms have been observed along the BC coast (Taylor and Harrison 2002). Local example: Heterosigma akashiwo.

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

Chromatophore An organelle within a phytoplankton cell that contains pigments and reflects light.

Cingulum (dinoflagellates) "In dinokont dinoflagellates, a furrow encircling the cell one or many times" (Horner 2002). It is also known as the girdle or transverse groove and may be located at, above, or below the midpoint of the cell with the left and right ends meeting or displaced form one another (Horner 2002). In diatoms, this term describes the collective elements of a diatom girdle: "The cingulum is made up of delicate silica bands that join the two valves of a frustule. Most diatoms possess a cingulum, although some may not" (Spaulding et al. 2010).

Claspers "A pair of membranous structures that clasp the otaria of the adjacent valve of linked cells" (e.g., Rhizosolenia; Horner 2002).

Coenocyte A multinucleate cell originating either from multiple nuclear divisions without accompanying cell division or from cellular aggregation and dissolution of the cell membranes inside the mass (DeWreede 2006).

Cosmopolitan Widely distributed; occurring in many parts in the world.

Costate ocellus "A plate of silica pierced by closely packed pores" with siliceous ribs between each row of pores (Tomas 1997).

Cribrum (cribra) (plural: cribrae) A perforated siliceous plate that blocks one of the many pores in a diatom's frustule (van den Hoek et al. 1995).

Cyst "A thick-walled dormant cell" (Horner 2002).

Cytoplasm In a eukaryotic cell, a gel-like substance within the cell membrane that contains all the organelles except for the nucleus.


Decussating Intersecting to form an"X" shape.

Desmokont In flagellated taxonomic groups, a cell type with two dissimilar flagella extending from the anterior part of the cell (Horner 2002): one flagellum extends forward and the other circles its base (Taylor 1980).

Diarrhetic Shellfish Poisoning (DSP) Mainly caused by okadaic acid, a toxin produced by some diatoms. When shellfish consume phytoplankton, they can bioconcentrate the toxin leading to non-life threatening symptoms that may include diarrhea, nausea, vomiting and cramps (Yasumoto et al. 1985).

Diel vertical migration (DVM) A daily vertical migration through the water column. Most commonly, this is used to describe zooplankton that spend their days at depth to avoid predators and spend their nights at the surface feeding on phytoplankton. This is called nocturnal DVM and the opposite (surface during the day, maximum depth during the night) is called reverse DVM (Selph 2009).

DIN (dissolved inorganic nitrogen) The total amount of nitrate (NO3-), nitrite (NO2-) and ammonia (NH3) dissolved in the water.

Dinokont In flagellated taxonomic groups, the type of cell with two flagella extending ventrally: one flagellum is in the cingulum and loops around the cell (transverse flagellum); the other is in the sulcus and trails behind the cell (trailing or longitudinal flagellum; Horner 2002).

DIP (dissolved inorganic phosphorous) The total concentration of all orthophosphates (PO43-, e.g., HPO42-, H2PO4-, H3PO4, etc.) dissolved in the water (Harrison et al. 2005).

Diploid Containing two identical sets of chromosomes (2n, where n is the number of unique chromosomes). For example, humans are diploid and have 23 unique chromosomes (n = 23), so most cells in your body each have 46 chromosomes (2n = 46). Gametes (sperm and eggs) are haploid (1n = 23). See also Haploid and Ploidy.

Discoid Disc-shaped.

Discolouration Change of water colour due to an algal bloom.

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).

Dorsal Relating to the back portion of the cell; opposite to the ventral side.

Downwelling The process of accumulating and sinking higher density material below lower density material. Due to winds and the earth's rotation, water can build up in coastal areas. This water sinks, taking plankton and nutrients out of the euphotic zone.


Embayment "Enclosed areas along the shoreline where freshwater from groundwater and streams is mixed with salt water from the surrounding oceans" (McCaffery and Livingston 2000).

Encystment The act of forming a cyst.

Endogenous Originating from within an organism. Opposite of exogenous.

Epicone In naked dinoflagellates, the anterior part of a dinokont cell above the cingulum. The equivalent of an epitheca for thecate dinoflagellates.

Epipelic Growing on mud (Spaulding et al. 2010).

Epitheca In thecate dinoflagellates, the anterior part of a dinokont cell above the cingulum. The equivalent of epicone for naked dinoflagellates.

Epivalve In diatoms, the older and larger valve and its girdle elements. This valve originally formed after cell division but has existed for several cell cycles (Horner 2002).

Estuarine Of or relating to estuaries.

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

Eukaryote/eukaryotic An organism that has membrane-bound organelles.

Euphotic The zone near the surface of the water where the light intensity is sufficient to support net photosynthesis (Letelier et al. 2004). Defined as the area above "the depth at which the photon flux equals 1% of the flux measured just above the air-sea interface" (Ryther 1956).

Euryhaline Describing organisms that are able to withstand a wide range of salinities in the environment (e.g., fresh, brackish, salt).

Eurythermal Describing organisms that are able to withstand a wide range of temperatures in the environment.

Eutrophic/eutrophication Water that is enriched in natural or artificial mineral and organic matter, which promotes an abundance of plant life (i.e., algae), and can result in reduced oxygen conditions.

Excentric Off-centre (pers. comm. D. Cassis).

Exogenous Originating from outside an organism. Opposite of endogenous.


Fimbriate Having a margin of fringe around the cell.

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

Foramen (plural: foramina) The space within an areolation or hole. Often used to describe features on diatom frustules and dinoflagellate thecae (Hasle and Syvertsen 1996).

Freshet A great rise or overflow of a river from heavy rains or spring thaw. In the Strait of Georgia, this usually occurs from March to June. (pers. comm. D. Cassis).

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

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


Gamete A reproductive cell (sperm or ovum) that can combine with another reproductive cell to create a new individual.

Girdle 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).

Girdle bands The connecting elements between two valves of a diatom cell. "They enclose and protect the cell and also accommodate the increase in cell volume during the cell cycle" (Horner 2002).

Globular Having a generally spherical shape; resembling a viscous drop of liquid.

Granular Made of small-sized particles (grains) or having the texture of something made of small grains.


Halocline (halo- salt; -cline gradient) The depth in the water column at which the salinity changes rapidly. Because saltier water is denser that fresher water, layers of different salinity will often stay as distinct layers and not mix.

Haploid Containing one set of chromosomes (1n, where n is the number of unique chromosomes). For example, human gametes (sperm and eggs) are haploid and have 23 unique chromosomes (1n = 23). See also Diploid and Ploidy.

Harmful Algae Bloom (HAB) The rapid growth and/or accumulation of algae in areas of constricted flow which may be harmful to the environment, animals, plants or humans by depleting oxygen, obstructing sunlight, and (in some cases) releasing toxins (Heisler et al. 2008).

Helical Coil- or spring-shaped.

Heterokont Describing a cell with two differently structured flagella (e.g., one covered in hairs and one smooth; Horner 2002).

Heterothallic (hetero- different; thallos green shoot or twig) Describing an organism that has male and female reproductive parts on different parts of the organism.

Heterotroph/heterotrophic An organism that cannot convert inorganic carbon into a usable energy source. Instead, it consumes other organisms to obtain organic carbon for growth.

Heterotypic 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.

Homotypic 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).

Horns The apical or antapical extensions found in some armoured dinoflagellates; they contain cytoplasm, are covered in thecal plates and can be hollow or partially solid (Horner 2002).

Hyaline Resembling glass; transparent or translucent.

Hypocone In naked dinoflagellates, the posterior part of a dinokont cell above the cingulum. The equivalent of a hypotheca for thecate dinoflagellates.

Hypotheca In thecate dinoflagellates, the posterior part of a dinokont cell above the cingulum. The equivalent of a hypocone for naked dinoflagellates.

Hypovalve In diatoms, the newer and smaller valve and its girdle elements. This valve formed after the most recent cell division (Horner 2002).


Imbrication lines In dinoflagellates, the overlapping arrangement between adjacent thecal plates (Tomas 1997).

Incertae sedis Latin for "of uncertain placement." This is used when a taxonomic group's relationships are not clear.

Intercalary bands Girdle bands that are furthest away from the valve (Smithsonian 2011).

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

Irradiance Amount of solar energy per unit area on a surface (units: μE m-2 sec-1, where E is an Einstein, a mole of photons).

Isogamy The simplest type of sexual reproduction between gametes that are similar in size and shape. Instead of being classified as male and female cells, organisms of different mating types (i.e., different size and shape of gamete) can fuse to form a zygote (Botany Dictionary 2002).

Isokont Describing a cell having flagella of the same kind and length (Horner 2002).



Kleptochloroplastidic Describing a phytoplankton that steals the chloroplasts of a photoautotrophic phytoplankton. The former does not produce its own chloroplast, but keeps the "stolen" chloroplasts alive in order to photosynthesize. Thus, it is considered a mixotrophic organism because it is able to both photosynthesize and consume organic matter (pers. comm. J. Shiller).


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).

Lanceolate Lance-shaped. Having a wider rounded base and tapering towards the tip.

Lateral Relating to a side-to-side direction.

Lipophilic Having the ability to combine with or dissolve lipids.

Littoral Describing the part of an ocean, river, or lake that is close to the shore. This can also refer to the organisms that live there. The littoral zone includes everything from the high water mark to near-shore areas that are permanently underwater. There is no fixed distance from shore or water depth that defines the end of the littoral zone. See also Neritic, which is directly below littoral.

LM (light microscopy) "Using a microscope in which a beam of light passes through optical lenses to view an image of the specimen" (MCM LTER 2010).

Lugol's iodine solution A solution of elemental iodine and potassium iodide in water; it was first used in 1829 by French physician Jean Lugol as a disinfectant. Lugol's iodine can be used as fixative to preserve phytoplankton samples for visual analysis at a later time (Leakey et al. 1994).

Lux (abbreviated 'lx') Units for measuring light intensity in a given surface area.


Mantle In diatoms, "the part of a valve that extends from the valve face, forming the valve edge." It is visible when the frustule is viewed in girdle view (Spaulding 2010).

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

Marginal process In some diatoms, a long, coarse external tube through the frustule (Tomas 1997).

Marginal ridge In diatoms, a ridge between the valve face and mantle (Hasle and Syvertsen 1996).

Mixotroph/mixotrophic An organism that is both autotrophic (photosynthesizes or chemosynthesizes) and heterotrophic. That is, it can gain energy both from light (or chemical) energy and also by consuming other organisms. This allows such organisms to take advantage of different environmental conditions.

Monocyclic alkene A class of molecules that contain one ring of carbon and hydrogen atoms. Monocyclic alkenes may contribute to mortalities of marine organisms. Rhizosolenia species produce these chemicals (EOL 2012).

Mucilage pad In diatoms, a structure joining adjacent cells or attaching a solitary cell to a substrate through the secretion of mucilage (can be a mucilage stalk in this case). These pads and stalks are produced by strutted processes (Round 1981).

Multinucleate Describing an organism containing multiple nuclei. This occurs after a cell division in which the cytoplasm was not divided to form separate daughter cells.


Naked (athecate, unarmoured dinoflagellates) Without a theca. Referring to "cells without a cell wall" (Horner 2002). The opposite of thecate or armoured.

Nekton Organisms that can swim independently of the current. Compare with plankton.

Nematocyst An ejectable organelle with stinging, sticky threads. Nematocysts are used by some dinoflagellates to capture prey (Smithsonian 2012). This term is primarily used to describe specialized stinging cells in jellyfish.

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).

Nucleus (plural: nuclei) In eukaryotic cells, a membrane-bound organelle that contains the cell's genetic information; the nucleus controls the activities of the cell by controlling gene expression.

Nutrients Various chemical substances that an organism needs for metabolism (i.e., to live and grow). These are usually taken up from the environment. Some examples include nitrate, phosphate, silica (for diatoms), iron, copper, etc. Some nutrients, like copper, are required for growth, but can also be toxic at high levels.


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

Occluded Blocked.

Okadoic acid A polyether fatty acid that is produced by some species of dinoflagellates. The toxin responsible for Diarrhetic Shellfish Poisoning (DSP; Cohen et al. 1990).

Oligotrophic Describing an aquatic ecosystem with low nutrient and organic matter accumulation and high dissolved oxygen content.

Organelle A unit within the cell that serves a specific function and is usually enclosed by an individual lipid bilayer (membrane).

Otarium (plural: otaria) In Rhizosolenia and related diatoms, an elongated, membranous thickening of the cell wall near the base of an external process. Otaria were previously called "wings" and can be seen as small lobes at the base of the needle-like spine at each end of a Rhizosolenia cell (Hasle and Syvertsen 1996).

Ovoid Oval or egg-shaped.


Pallium (feeding) A mode of feeding used by some heterotrophic dinoflagellates. The dinoflagellate extrudes its cytoplasm, engulfing its food (often a cell or chain of cells). The food is digested outside the dinoflagellate's cell. The dinoflagellate then pulls its cytoplasm and its newly digested meal back inside its theca. This method of feeding allows dinoflagellates to eat food that is bigger than itself.

PAR (photosynthetically active radiation) Describing the spectral range of sunlight (400 - 700 nm) that photosynthetic organisms can use for photosynthesis; lower wavelengths can damage plant tissue and higher wavelengths do not carry enough energy to support photosynthesis. This approximately corresponds to the range of visible light.

Paralytic Shellfish Poison (PSP) Results from human consumption of filter-feeding shellfish that have fed on toxic saxitoxin-producing dinoflagellates. During certain phytoplankton blooms, shellfish can accumulate and bio-concentrate the toxins. The main species associated with PSP in Canada are dinoflagellates in the genus Alexandrium. "Symptoms of PSP begin with a tingling sensation or numbness around the lips within 5 - 30 minutes of ingestion, gradually spreading to the face and neck. With moderate to severe intoxication, symptoms include incoherent speech, stiffness and non-coordination of limbs and slight respiratory difficulty. Gastrointestinal symptoms of nausea, vomiting, diarrhea and abdominal pain are less common. Following high intake, paralysis of respiratory muscles may progress to respiratory arrest and death within 2 - 12 hours after consumption" (DFO 2010).

Pectenotoxins (PTX) A group of polyether-lactone toxins that have been detected in microalgae in Australia, Japan, New Zealand and in a number of European countries. They are exclusively produced by Dinophysis species and can be found in filter-feeding bivalve molluscs (e.g., oysters or mussels). There are no reports of human illness causally associated with exposure to these toxins. Pectenotoxins co-occur with the okadaic acid group of toxins, which makes it difficult to assess whether the PTX-group toxins contribute to human cases of diarrhetic shellfish poisoning (DSP; EFSA 2009b).

Peduncle A stalk or narrow part that supports a larger part of the organism. Can also refer to the feeding tube of certain dinoflagellates.

Pelagic Describing an ecosystem or species that is far from the bottom or shore of a water body. In an open aquatic environment.

Pennate (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.

Perforated Describing a surface that contains many holes. Synonym: areolated.

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

Phagotrophic Describing an organism that feeds by engulfing its food items. Once surrounded, a food particle is then ingested inside a vacuole. Many flagellates are phagotrophs.

Photoautotrophic Describing organisms that create their own energy from light via photosynthesis.

Photoperiod 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.

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.

Picoplankton Phytoplankton within the size range of 0.2 to 2 μm which may be autotrophic, heterotrophic or mixotrophic. They are often found in oligotrophic regions because of their high surface-area-to-volume ratio that better enables them to make use of limited nutrients available (Callieri and Stockner 2002).

Plankton Organisms that drift at the mercy of the currents.

Plasmolysis The shrinking of the protoplasm away from the cell wall of an organism due to water loss from osmosis (when the cell has greater water pressure than its surroundings). This results in gaps between the cell wall and the cell membrane (Spaulding et al. 2010).

Ploidy The number of identical sets of chromosomes a cell or organism contains (n). This varies between organisms and throughout an organism's life cycle. For example, humans are diploid (2n), but our reproductive cells (sperm and eggs) are haploid (1n). See also Diploid and Haploid.

Plume The freshwater from a river that extends past the river mouth or estuary. That freshwater often carries sediments, colouring the water brown. For example, if you cross the Strait of Georgia by ferry or by plane, you can see a distinct change in the water between the brown Fraser River plume and the green salty ocean water.

Poroid A simple hole through the surface of a diatom valve (Smithsonian 2011).

Poroid areola(e) In diatoms, a pore or hole through the frustule. The pore can be cylindrical or cone-shaped and has a thin layer of perforated silica across it (Tomas 1997).

Posterior The back end of a cell. Opposite of anterior.

Process A natural projection or appendage on an organism.

Prokaryote/prokaryotic An organism that lacks a nucleus and other membrane-bound organelles.

Protist A diverse group of eukaryotic microorganisms which range from "animal-like" protozoa to "plant-like" algae. This is an older, informal term referring to many simple organisms that do not fit well into the kingdoms of plants, animals or fungi. This means that diatoms, dinoflagellates, amoebae, ciliates, slime moulds, and many other groups of organisms can be called protists.

Protoplasm A general term describing the living substance of the cell. In a eukaryotic cell, this includes the nucleoplasm and the cytoplasm (Fink 1925). Contents include ions, amino acids, nucleic acids, lipids and water (Man Anatomy 2010).

Pseudopodium/pseudopodia A semi-permanent extension of the cytoplasm used for locomotion and feeding by some flagellate protozoans.

Punctated Marked with tiny coloured spots or depressions.

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

Pustule A blister- or knob-like projection on the cell surface (Protistiary 2011).

Pycnocline (pycno- dense; -cline gradient) The depth in the water column at which the density changes rapidly. This density gradient can be caused by temperature (thermocline), salinity (halocline) or both. Because of the difference in density, bodies of water will often stay as distinct layers and not mix.

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


Quota (as in, cell quota for a nutrient) The amount of a macro- or micronutrient required by an organism to fulfill its life cycle.


r/K selection theory Describes a logistic growth model that is based on r (the intrinsic rate of population growth) and K (the carrying capacity of the environment). According to this model, all species are subject to natural selection; thus different life history strategies evolve to adapt each species to its niche. The r-strategists lie at one extreme and exhibit temporary colonizing behavior with "booms" and "busts" in population size. They are usually smaller in size, have shorter generation times, and allocate available energy resources to reproductive activities. Conversely, the K-strategists live in environments where mortality factors are relatively stable. They are usually larger in size, favour longer generation times and allocate available energy resourced to enhancing survival through increased competitive ability (e.g., defensive mechanisms; Gunderson 1980). For example, weeds are r-strategists and large trees are K-strategists.

Radial (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.

Raphe "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).

Reactive oxygen species Chemically reactive compounds that contain oxygen (i.e., oxygen ions or peroxides). They are natural byproducts of oxygen metabolism. Levels in the cell may increase with increased environmental stress (Apel and Hirt 2004).

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).

Reticulated Resembling a net or having a pattern that resembles a net.

Rhomboid/rhombic Describing the geometric shape of the cell; a parallelogram in which adjacent sides are of unequal lengths and angles are oblique.

Ribs Features that provide support to other structures in the cell.


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).

Saxitoxin (STX) A class of potent neurotoxins that prevent the entry of sodium ions into nerve cells and can cause paralytic symptoms in humans. They are mainly produced by dinoflagellates belonging to the genus Alexandrium. When filter-feeding bivalve molluscs (e.g., oysters or mussels) consume these dinoflagellates, saxitoxins can be bio-concentrated and transferred up the trophic level to reach humans (EFSA 2009a).

Sedimentation (settling out) The tendency for particles to settle out of the water column and come to rest at the bottom due to gravitational forces. Factors that influence the rate of sedimentation are particle size, water density and currents.

SEM (scanning electron microscope) A microscope which applies "a focused beam of high-energy electrons to generate a variety of signals at the surface of solid specimens" (NSF 2011).

Semiendogenous A type of spore production in diatoms where "one valve of the mature spore [is] enclosed within the parent cell, the other valve [is] free." Compare with endogenous (the mature spore is enclosed in the parent cell) and exogenous (the mature spore is not enclosed by the frustule of the parent cell; Round et al. 2000).

Sigmoid S-shaped.

Siliceous Describing the character (i.e., white, shimmery) or chemical presence silicon dioxide (SiO2) as a component of phytoplankton cell covering.

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).

Species succession For the phytoplankton community, this refers to the natural progression of species in the environment determined by the level of compatibility to environmental conditions. Community composition varies seasonally depending on temperature, light and nutrient availability.

Spicules Small, needlelike structures.

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

Spinula (plural: spinulae) A small spine or hook.

Statospore An internally formed spore in its resting stage. A thick-walled, resistant spore formed within the frustules of various centric diatoms.

Stellate Star-shaped.

Sternum In pennate diatoms, the thickened silica structure that usually extends along the apical axis and may be centrally or marginally positioned. In diatoms with raphes, the sternum contains the raphe (Spaulding et al. 2010).

Stratification The development of distinct non-mixing layers in the water column resulting from a steep gradient in density, which is caused by differences in temperature and/or salinity.

Striae (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).

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).

Subcentral Near, but not at, the centre.

Subfusiform Describes a tube shape that widens at both ends and tapers in the middle.

Substrate Bottom surface. For example, the substrate can be rock, sand, mud, etc.

Sulcal list (left and right) In dinokont dinoflagellates, a well-defined groove on the ventral surface that is supported by ribs.

Sulcus "In dinokont dinoflagellates, the longitudinal area on the ventral surface that forms a furrow or depression and houses the longitudinal (trailing) flagellum" (Horner 2002).


Tabulation (plate formula-based dinoflagellate taxonomy) In dinokont dinoflagellates, the arrangement of theca plates forms a distinctive geometry or topology that is unique to a genus. This is used as a main means for classification (Horner 2002).

TEM (transmission electron microscope) A high-resolution microscope that works by passing a beam of electrons through a very thin specimen (CMRA 1995).

Thallus (plural: thalli) (thallos green shoot or twig) Undifferentiated vegetative tissue. This term applies to algae, fungus, and some lichen. Compare with vascular plants (like trees and flowers), which have differentiated tissue.

Theca (plural: thecae) Cell wall. In dinoflagellates, it is composed of cellulose plates within vesicles (Horner 2002).

Thecal Of or relating to the theca.

Thermocline (thermo- temperature; -cline gradient) The depth in the water column at which the temperature changes rapidly. Because colder water is denser that warmer water, layers of different temperature will often stay as distinct layers and not mix.

Trailing flagellum In dinoflagellates, one of two flagella they possess; responsible for the movement of the cell and due to its asymmetric arrangement it also causes a rotation of the cell around an axis perpendicular to the longitudinal axis. (Fenchel 2001).

Transapical axis In diatoms, the longitudinal axis of the valve.

Transverse flagellum In dinoflagellates, one of the two flagella they possess; responsible for the rotation of the cell around its length axis. The two flagella are directed parallel to one another and together, the rotational components result in a helical swimming path (Fenchel 2001).


Unialgal Related to a single phytoplankton cell. For example, a unialgal culture is one derived from a single cell.

Upwelling A wind-driven mechanism of mixing the water column. Cold, dense, nutrient-rich, and often oxygen-poor water from depths rises to replace the warmer nutrient-poor surface water. This input of nutrients can have a significantly increase primary productivity in a region (Dugdale 1985).


Vacuole A membrane-bound organelle found in some protists, containing a water solution of organic and inorganic molecules (including enzymes). In some cases, vacuoles may contain engulfed solids (Falkowski et al. 2004).

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

Valvocopula In diatoms, a band next to the valve that may help link the valves together (Hasle and Syvertsen 1996).

Ventral Relating to the underside of an organism; abdominal.


Water column Referring to a water system from the surface to the bottom sediments. This can be used to understand processes of stratification, mixing and their relationship to nutrient transport. Temperature, salinity, pH, and nutrient levels often vary along the length of the water column.



Yessotoxins (YTXs) A group of toxins produced by some dinoflagellates, including Protoceratium reticulatum. Researchers have observed toxic effects in mice but little is known about it effects on humans or how the toxins work. These toxins do not break down with freezing or cooking, which has lead some countries to regulate the amount of YTXs allowed in shellfish (EFSA 2008).



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