In Cyanobacteria cells, cylindrical structures whose protein walls are permeable only to gases. Their function is to regulate the buoyancy of the cells and collect carbon dioxide. They most often occur in planktonic species. Because they refract light, they often appear irregular in shape and very dark. The older term is ‘gas vesicles’.

In some Cyanobacteria, it is a thick-walled, resistant, dormant or resting cell which develops from vegetative cells generally when they are exposed to unfavorable environments. It may be part of a filament or released by a filament. Germination may occur after the dormant stage.

A growth form or thallus of closely interwoven algal filaments.

In Cyanobacteria, it is a blue phycobilin-type pigment.

A surface that is pitted or covered with many small pores or cavities.

An object that is without clear form; shapeless.

A term used to describe an environment that is without free oxygen. Also, a term used to describe a type of metabolism that doesn’t require oxygen (facultative) or requires the absence of oxygen (obligate).

The combination or fusing of multiple, separate branches, sheathes or filaments into a single filament; like tributaries forming a single river

The cell at the upper end of a filament or filament; opposite the basal cell

In Cyanobacteria, the tendency to develop akinetes or other structures either between two heterocysts or near the heterocysts

An object that is curved like a bow or crescent-shaped.

The cell at the lower end of a filament or filament; opposite end of the apical cell.

The community of organisms that inhabit the lowest water levels of a marine or freshwater system including the sediment surface and some of the layers just under the sediment surface.

The processes of crystal formation from solution mediated by organisms.

Regarding algae, it is the condition where a single species (or very few species) undergoes such explosive multiplication that it becomes the dominant organism in that body of water for that period of time. Because these are normally planktonic algae, they tend to form a surface scum.

A term describing water found in estuaries, mangrove swamps, etc. The salinity is measured at 500-30,000 parts per million (ppm) of NaCl salt plus many others salts.

A term describing water found in hypersaline lakes. The salinity is measured at > 50,000 ppm of NaCl salt plus many others salts.

An object has a puckered or blistered appearance.

A term used to describe a growth form that is clustered, in thick tufts or clumps, or forms a turf.

A thickened outer cell wall of a terminal filament cell.

A terminal cell with a distinctly spherical, knob-like or swollen end.

In cyanobacteria, the center region of the cell that is usually less pigmented than the chromatoplasma.

In algae (and most higher plants) it is the main photosynthetic pigment.

In Cyanobacteria, a region in a cell, often on the periphery, where pigment particles tend to collect

Is a term for an object that has irregular perforations or lattice-like openings on its surface. It is also a colonial algal species whose cells inhabit the interstices or cavities of the lattice of another species’ colony.

An object that is heart-shaped\" or valentine-shaped.\"

An object whose edges are wavy, scalloped or notched

An object that is in the form of a cross or a small case ‘t’; also cruciform.

A surface-covering algal body (thallus) made up of cell layers; often dried.

The community of organisms that inhabit the snow in snowfields. These are usually at high latitudes or elevations. They are also said to be cryophilic.

An object that is narrowly triangular; wedged-shaped.

In cyanobacteria, a type of carbohydrate that is more similar to glycogen than starch. Therefore, it does not turn dark when treated with iodine.

Dead and partially decaying organic material.

Something that is mushy or in the process of dissolving; liquefaction, deliquescence. It flows apart or dissolves off a structure.

Tap water: the average salinity is measured at <100 ppm of NaCl salt plus many others salts.

The cyanobacteria that live within the mucilage of other freshwater algae

The community of organisms that live within the pores and cracks of rocks

An organism that lives within another organism in a mutually beneficial relationship. Examples of this are lichens where green algae or cyanobacteria live within fungi.

An organism that grows on wood or trees; also epidendron

In a thermally stratified lake (one layered by temperature), it is the upper, warmer and more mixed surface layer. It is above the thermocline (the boundary between the epilimnion and lower, cooler hypolimnion). The epilimnion tends to be brighter, have higher dissolved oxygen concentrations, but lower nutrient concentrations.

An organism that grows on rock surfaces or substrates; also epilithon

An organism that grows on sediments, clays and silts; also epipelon

The community of organisms that live on submerged macrophytes (vascular plants) in fresh waters. It is a subset of the periphyton.

An organism that grows attached to or among sand grains; also episammon.

An organism whose cells have lipid membranes enclosing their organelles, particularly the nucleus.

An organism that is capable of completing its life cycle in the water column.

The condition of a body of water (usually lakes) which has relatively high levels of dissolved nutrients and organic production (generally photosynthesis).

The process whereby a body of water develops relatively high levels of dissolved nutrients and organic production and becomes eutrophic.

In Cyanobacteria, they are daughter cells that divide externally from distinctly polarized cells (e.g., the genus Chamaesiphon). They are produced singly or successively in rows.

Exhibiting a trait or ability under some conditions but not under others; optional. It is the opposite of obligate. For example, a facultative heterotroph is an organism with the ability to use photosynthesis as its primary source of energy, but can also acquire organic material from external sources when the need arises; perhaps under low light intensity.

In Cyanobacteria, a break in a filament followed by subsequent longitudinal growth produces one or both filament ends projecting out from the sheath. This gives the false appearance of branching. The only connection between cells in false branching is the sheath. Compare to True Branching.

In filamentous algae, a bundle or cluster of many filaments

In filamentous algae, a term that describes an organism that exists in clusters of filaments or fascicles, like Aphanizomenon.

In Cyanobacteria, a broader term for a string of cells

An object that is thread-like; a filament

An object that has a border with hairs or hair-like appendages along it; fringed in appearance

A term describing water found in lakes, ponds, etc. The salinity is measured at 0-500 ppm of NaCl salt plus many others salts.

An object that is widest at the middle and tapering at both ends; spindle-shaped.

In planktonic cyanobacteria, a spherical or cylindrical structure that holds gas (often CO2) in the cytoplasm. They often cluster and are called aerotopes. They appear dark (red, brown, black) because they refract light. Their function is to provide buoyancy and store CO2.

An object that is spherical; in the form of a globe.

A dark blue pigment found in the sheath of some cyanobacteria.

Objects in a compact group; a bunch or cluster.

A protein with a carbohydrate attached to it. They are often found in the cell wall or in an external gelatinous sheath.

A thin, elongate, usually clear, colorless, terminal cell. It increases surface area to increase gas and/or nutrient exchange. It is produced in times of deficiency.

Organisms able to survive in high ionic strength environments; one example would be a salt lake.

The community of organisms that live on submerged hard substrata.

In Cyanobacteria, thick-walled, yellowish-translucent cells with a gelatinous plug at both ends; it is the site of N2-fixation. It is also called a heterocyte.

An object that is not symmetric to the longitudinal axis. There is a difference in shape between the upper (apical) and lower (basal) parts of an organism. (See genus Rivularia.)

A structure that attaches a thallus to the substratum

In some filamentous cyanobacteria, they are filaments whose function is vegetative (asexual) replication. They are formed by filament fragmentation and dispersal. This differentiation usually takes place in response to environmental stressors. Some are motile (gliding). This is a key step in the development of N2-fixing plant/ Cyanobacteria symbioses (e.g., Nostoc and its plant host).

An object that is clear and colorless: usually a cell.

A term describing water found in brine lakes. The salinity is measured at >50,000 ppm of NaCl salt plus many others salts.

In a thermally stratified lake (one layered by temperature), it is the lower or deeper layer. It is below the thermocline (the boundary between the epilimnion and lower, cooler hypolimnion). The hypolimnion tends to be darker, have lower dissolved oxygen levels, but higher nutrient levels.

Objects that are overlapping; like shingles on a roof or scales on a fish.

An object that is swollen; thickened in appearance.

A term describing an object that is between two or more others, inserted between, interposed. In filamentous cyanobacteria, this term describes the middle of the filament or filament.

An object that is screw-shaped or helical.

A filament whose diameter is more or less constant along its entire length

An object that is symmetric to the longitudinal axis. The filament diameter is consistent throughout. It does not taper toward the ends

An aquatic environment that is well-oxygenated, but lacks organic matter

An opening or cavity

A lake environment; it implies standing water.

An arrangement or structure composed of usually thin, homogeneous layers, plates or scales.

An object that is wider at or near the middle than the ends.

An object that is lens-shaped; thinning to a point at the ends.

An organism formed by the mutually beneficial symbiotic relationship between a fungus and either cyanbacterium or green algae.

The open water portion of a lake; also called a Pelagic Zone.

A diverse group of molecules primarily made of hydrogen and carbon (hydrocarbons). They are not soluble in water, thus, they are said to be ‘hydrophobic’. Lipids are a building block of living cells and affect much of their structure and function. Lipids include fats, oils, waxes, vitamins and most of the non-protein cell membranes.

The shallow water area that extends from the shore to the outward limit of the rooted vascular aquatic plants.

A running water systems: springs, streams and rivers.

A calcium carbonate (CaCO3) deposit on surfaces in hard water or alkaline lakes or streams. This is a white, gritty precipitate.

A region of actively dividing, undifferentiated cells

An aquatic environment characterized by moderately polluted habitats. It is divided into at least two subgroups. Alpha-mesosaprobic zones are characterized by vigorous oxidation processes, higher dissolved O2 levels (though O2 consumption is still high), no hydrogen sulfide production and the beginning of NH3 oxidation. Cyanobacteria are dominant here. Beta-mesosaprobic zones are characterized by high dissolved O2 levels, low O2 consumption, mineralization of organic materials and higher levels of the end-products of mineralization (e.g., nitrates). Diatoms and green algae are dominant here.

A body of water (usually lakes) with intermediate levels of dissolved nutrients and organic production (photosynthesis)

A term describing an organism made up of similarly shaped structural units stacked up in longitudinal series.

Aggregations of normally planktonic algae pushed into the littoral zone. They are neither strictly attached to substrata nor truly suspended in water.

A term describing an organism made up of similarly shaped structural units which are jointed or constricted at regular intervals. This structural pattern resembles necklace beads on a string.

In Cyanobacteria, an amorphous, mucopolysaccharide/protein substance covering or surrounding certain cells

A cell that undergoes programmed cell death (apoptosis) to release hormogonia; also called necridia.

Planktonic organisms which live at the air-water interface

The biochemical process used by bacteria to convert biologically unusable, atmospheric nitrogen (N2) to biologically useable nitrogen in the form of ammonia (NH4+).

An organism that can only acquire organic material from external sources, that is, non-photosynthetic

An object that is ovoid or egg-shaped, but with the broader end toward the top; inversely ovoid, also obovate.

An aquatic environment characterized by high dissolved oxygen levels, low organic material levels and low fermentation rates. The mineralization processes are complete and O2 consumption is nearly zero. Alpha-oligosaprobic zones are characterized by comparatively large species diversity and high bioactivity. Beta-oligosaprobic zones are characterized by lower to moderate species diversity and low bioactivity.

A body of water (usually a lake) that has low levels of dissolved nutrients and organic production (photosynthesis). These lakes tend to be deep, steep-sided, transparent and with little or no littoral zone.

A lipid membrane-bound structure inside cells with a specific function such as a nucleus or chloroplast.

An object that is egg-shaped.

In filamentous cyanobacteria, it is the tendency to develop akinetes around or near heterocysts.

A unit to measure the small amounts within much greater amounts. Literally it is one unit of volume within one million units. Other ways of expressing this is 0.0001%, 32 seconds out of a year or one drop in 13 gallons.

The open water portion of a lake; also a Limnetic Zone.

A group of objects gathered in a small tuft; brush-like.

The community of organisms that live on a wide variety of substrata (especially macrophytes) in fresh waters

In cyanobacteria, it is the ability of organisms to change the relative amounts of photosynthetic pigments on display in response to the intensity of sunlight available to them. This may result in changes (color) to their appearance.

An organism that has the ability to synthesize their own organic compounds (food) through photosynthesis

An organism that has the ability to both synthesize their own organic compounds (food) through photosynthesis and metabolize external sources of organic molecules to meet the needs of the organism.

The movement of an organism or a cell toward or away from a light source

The water soluble accessory pigments coupled to protein structures that aid in photosynthesis. The pigments are phycoerythrin (red), phycocyanin (blue) and allophycocyanin.

In cyanobacteria, the granular structures on the thylakoids made up the phycobiliprotein accessory pigments

A pilus (plural = pili) is a hair-like appendage found on the surface of many bacteria. It can be involved in locomotion or conjugation.

The individual organisms that make up the community of organisms that live free-floating in the upper water column. They can be either algal (phytoplankton) or animal (zooplankton).

The community of organisms that live free-floating in the upper water column: literally, ‘to drift’. It is sometimes referred to as planktic.

A term describing objects that are folded, has furrows or gives the appearance of folds or furrowing.

An aquatic environment characterized by heavy pollution with sewage or other organic materials, mass growth of the bacteria that are involved in decomposition processes, a high rate of oxygen consumption and high production of ammonia and hydrogen sulfide. This zone is almost completely lacking in cyanobacteria except for Arthrospira. Bacteria and protozoa are the most common organisms in this zone.

The community of minute organisms that live in the water filling the interstices of sand and sediment particles adjacent to a body of fresh water (a beach). It is sometimes considered to be a part of benthos.

The branches grow as strongly as the stem from which they arise. This type of branching yields a characteristic ‘Y’ shape. This falsely resembles dichotomous branching and is, therefore, ‘pseudodichotomous’.

A loose chain of cells held together by a common gelatinous matrix, fibrils or another connection. The cells are typically separated from each other. Unlike true filaments, they do not share a common cross wall.

In Cyanobacteria, an opening at the apical end of a filament sheath that facilitates the release of a reproductive cell (an exocyte)

An object that is pear-shaped.

An object that is bean or kidney-shaped.

An object that is net-like or forms a network.

An object that is ‘tube-like’ in shape or morphology.

A measure of the degree of saltiness or the concentration of dissolved salts in a body of water. It influences much of the physical, chemical and biological composition of oceans, lakes and rivers. Salinity also has similar influence on soil.

is the chemical compound formed by the attraction of electrically charged elements or ions. Mostly the term ‘salt’ refers to ionic bond between sodium (Na+) and chloride (Cl-). When dissolved in water they separate into their component ions. Salt also describes the chemical compounds formed between other ions such as potassium (K+) or magnesium (Mg2+).

A term describing water found in oceans. The salinity is measured at 30,000 - 50,000 ppm of NaCl salt plus many others salts. The average ocean salinity is 34,700 ppm of NaCl salt plus many others salts.

An object that is surface pitted or furrowed with numerous small depressions.

In certain cyanobacteria it is a yellow-brown pigment in the sheath that may be a shield against UV radiation.

In Cyanobacteria, a form-fitting mucilaginous, polysaccharide enclosure that covers cells, colonies or filaments. It may be loose or firm, very broad or quite narrow and clear/ colorless or pigmented.

A supporting stalk often between the holdfast and thallus.

In lakes it is the condition in which the lake water becomes separated into two (or more) strata or layers based on their temperature and density. The upper, warmer, less dense water comes to the surface while the cooler, more nutrient-rich and denser water settles to the bottom.

The community of organisms that live on damp surfaces not submerged in water such as rocks and walls. The term subaerial also describes this condition.

A filament with akinetes or heterocysts shifted to one end or the other.

The area just beyond the intertidal zone (the spray or supratidal zone)

In Cyanobacteria, it is a vegetative body with no true tissues (no differentiation); a conglomeration of cells and/or filaments.

In a stratified lake it is the boundary layer between the upper, warmer water and the lower, cooler water.

In cyanobacteria there are portions of the external membranes which fold back on themselves and extend into the protoplasm in a somewhat regular or organized manner. On these surfaces (called thylakoids) the photosynthetic pigment complexes are displayed to capture solar energy.

The term for the calcium carbonate (CaCO3) precipitated from certain alkaline waters. In many cases cyanobacteria play a role in the precipitation process.

A linear array of cyanobacteria cells joined by their end walls with plasmodesmata, with or without sheath. Also known as a Filament.

This is the product of lateral cell divisions off the main axis of the filament. There is a physiological connection maintained between a true branch and the trunk. The only connection between a false branch and the trunk is the sheath. Compare to False Branching.

An organism that is usually non-planktonic (such as attached benthic organisms) that are carried into the plankton through disturbance of their habitat (wind, current, etc.). They are also said to be accidently planktonic\".\"

Structures formed/ arranged in a single row or on only one side of an axis.

In Cyanobacteria, it is a void or vesicle often containing gas.