Glossary

Areola (pl: areolae)

On a diatom valve: one of the pores within a row of multiple pores (such a row is called a stria). Areolae can occur in different shapes, such as round or elongated (like tiny slits).   

Benthic

Living on/at the bottom of a body of water.

Chloroplast

Membrane-bound organelles found in the cells of photosynthetic eukaryotes. These subcellular structures contain pigments that capture energy from sunlight.

Cilia (singular: cilium)

Short, hairlike structures projecting from the surface of some eukaryotic cells, including many non-photosynthetic protists. When it comes to these unicellular organisms, cilia are involved in feeding as well as in movement. Shorter than flagella, and present in greater numbers than flagella.
Compare to: flagella

Cingulum (pl: cingula)

In dinoflagellates: the transverse groove that runs around roughly the mid-line of the dinoflagellate cell, and within which lies the transverse flagellum.

In diatoms: collective name for the multiple siliceous bands—each of which is called a girdle band—associated with a diatom valve. The cingulum of one valve overlaps the cingulum of the other valve, and together the cingula form the girdle.

Coccoid

Refers to a type of cell that is characterized by a simple, rounded shape (may spherical or sub-spherical, or slightly elongated/rod-shaped). Used here mainly in the context of describing morphological classes of cyanobacteria (“coccoid cyanobacteria”) or green algae (“coccoid green algae”). 

Epiphytic

Growing on other plants (or plant-like organisms).

Compare to: metaphytic. 

Eukaryote

One of two types of living cells (the other type is prokaryotic). Eukaryotic cells possess membrane-bound organelles (such as a nucleus). Other than cyanobacteria, all groups of algae discussed here are eukaryotic.

Compare to: prokaryote  

Eyespot

This feature is found in a variety of algal cells; it is a specific spot which is sensitive to light and is usually red or reddish-orange in color. Also called a stigma.

Filamentous

Used here to refer generally to algae whose cells are arranged end-to-end in a linear fashion, thus forming a filament (like a string or chain of cells). Identification guides based on morphology often describe cyanobacteria as either coccoid or filamentous.

Flagellum (pl: flagella)

A long threadlike structure projecting from a variety of cells; amongst the algae, only eukaryotic types possess flagella (many bacteria do possess flagella, but cyanobacteria do not). Provides a mechanism of motility. Longer than cilia, and present in smaller numbers than cilia.

Compare to: cilia

Frustule

The silica-based cell wall of a diatom. 

Genus (pl: genera)

The taxonomic rank that is one “level” above species in the hierarchical system of classifying living organisms. When referring to a species by its scientific name, we use a system called binomial nomenclature, wherein each scientific name consists of two parts: genus name followed by species name. For example, Microcystis aeruginosa is one species within the genus Microcystis (genus and species names are always italicized, or underlined if handwritten). When identifying algae with a light microscope, it is often possible to identify specimens down to the level of genus.

Girdle

Formed by the overlapping cingula associated with each of the two valves of a diatom (one cingulum associated with each valve). When describing the morphology of a diatom, the frustule’s morphology is often described both “in girdle view” as well as “in valve view.” Put simply: if a diatom frustule were a can of soup, then “in girdle view” would mean that you are looking at the side of the can, where the label is. “In valve view” would mean looking directly at either the top or the bottom of the can. 

Lentic

(Type of aquatic environment) Standing waters, including lakes, ponds, and smaller bodies of water, such as small temporary pools--even something as small as a birdbath! 

Lorica

A protective structure surrounding some types of algal cells (such as Dinobryon). Derived from this is “loricate,” which simply means “possessing a lorica.” 

Lotic

(Type of aquatic environment) Running/flowing waters, such as rivers and streams.

Metaphytic

Growing among—in loose association with—aquatic plants or algae, but not attached to them.

Monophyletic

A taxonomic group consisting of an ancestor and all of its descendant species (the aforementioned ancestor is the most recent common ancestor shared by all those descendants). When newly gathered evidence suggests that a taxon is not monophyletic, taxonomic classifications are revised: taxa may be split (or combined) in order to (eventually!) achieve a system of classification wherein all included taxa are monophyletic.  

Compare to: polyphyletic, paraphyletic

Paramylon

A carbohydrate storage compound found in Euglenoid cells. Paramylon bodies are often visible in the light microscope as small Tic Tac-like grains, large rods, discs, or links, which appear colorless or whitish.

Paraphyletic

A taxonomic group containing some, but not all, of the descendants of a specified common ancestor.

Compare to: monophyletic, polyphyletic 

Pellicle

The outer layer of Euglenoid cells (not including the lorica, if present). This proteinaceous layer is arranged in strips, which gives many Euglenoid cells a “striped” appearance.

Periphytic

Growing or living upon submerged surfaces (rocks, for example). 

Phycology 

The scientific study of algae. Not to be confused with “psychology,” though Google will relentlessly ask you if that is what you meant to type.

Phytoplankton

Photosynthetic microorganisms found in the plankton of aquatic environments—“in the plankton” means that they are free-floating (not attached to other structures, plants, animals, or surfaces) in the water (suspended within the water rather than resting on the bottom of the waterbody). 

Planktic (Planktonic)

Floating freely in the water column.

Plastid

In general, a plastid is a special type of organelle. Many of these organelles contain photosynthetic pigments; a chloroplast is one example of a plastid. Here, we use this term mainly when discussing diatoms, because the word “plastid” is typically used in place of “chloroplast” when referring to diatoms. 

Polyphyletic

A taxonomic group whose members do not all share the same most recent common ancestor (i.e., some members of that group may be more closely related to organisms outside of that group than they are to each of the other organisms in that group).

Compare to: monophyletic, paraphyletic

Prokaryote

One of two types of living cells (the other type is eukaryotic). Prokaryotic cells do not possess membrane-bound organelles (such as: nucleus). Cyanobacteria are prokaryotes; all other groups of algae discussed here are eukaryotic.

Compare to: eukaryote  

Protist

Eukaryotic organisms that are not classified as plants, animals, or fungi. Eukaryotic algae are therefore included under the “protist” umbrella, though plants did arise from a lineage of green algae.

Pseudopod / pseudopodium (pl: pseudopods / pseudopodia)

In amoeboid protists: projections which arise from the cell temporarily and function to pull the cell along in a sliding manner.

Pyrenoid

A structure associated with the chloroplasts of some algae, often visible in the light microscope as a distinct circular protrusion (could be described as having a wart-like appearance). Within these structures, carbon dioxide is concentrated around an enzyme known as RuBisCO. This enzyme is involved in the process of carbon fixation: the photosynthetic conversion of atmospheric carbon dioxide into carbohydrates, which provide energy for plant and algal cells. 

Sessile

Describes an organism which lives attached to a surface, as opposed to moving around freely. For example, the ciliate Vorticella is sessile during parts of its life cycle, living attached to surfaces (such as plants or algae) via a contractile stalk.  

Stigma

See term: eyespot

Stria (pl: striae)

A row of areolae on a diatom valve.

Test

A shell-like structure surrounding the cells of some amoebae (referred to as testate amoebae). The brownish-orange tests of Arcella are frequently seen in water samples analyzed by NJCWST.  

Taxon (pl: taxa)

Any taxonomic unit (such as genus or species).

Thallus

The overall form, or body (of growth), of algae. For example: when describing cyanobacteria that form mat-like layers of filaments covering the substrate to which they are attached, one might say that "the thallus is in the form of a mat." This term can also be used to describe algae that exist as single cells, but here we use it mostly when describing many-celled aggregates (such as cyanobacterial mats or branched filamentous green algae). 

Valve

One of the two faces of a diatom frustule. Put simply: if a frustule were a can of soup, then the valves would be the top and bottom of the can (similarly, if the frustule were a sandwich, the valves would be the two slices of bread). Associated with each valve are girdle bands, collectively called cingula; the two cingula are collectively called the girdle.

Vascular tissue

A type of tissue responsible for transporting water and nutrients throughout the body of a plant. Plants which possess these tissue types are known as vascular plants, and most of the plants we pay any mind to—trees, houseplants, the grasses that make up our lawns—are included in this group. Amongst the land plants, only mosses, liverworts, and hornworts do not possess these tissue types, and these are called non-vascular plants.  

Vegetative 

In the context of eukaryotic algae, vegetative cells (or structures) are those that are growing, rather than those that are specialized for reproductive processes. Both sexual and asexual means of reproduction occur in eukaryotic algae (depending on the species), and these processes involve a variety of specialized cell types and/or reproductive structures—these are not referred to as vegetative cells/structures. Additionally, some taxa produce specialized cells equipped to endure harsh environments and then propagate themselves once conditions improve. Different types of specialized algal cells have their own special names (often ending in -spore). 

Similarly, some cyanobacteria produce specialized cells as a means of propagation (although unlike eukaryotic algae, they do not reproduce sexually). When referring to cyanobacteria, “vegetative” is also used to distinguish growing and dividing cells from heterocytes, which are cells specialized for the purpose of nitrogen fixation.  

“Vegetative reproduction” is a term that may be used in the context of either algae or higher plants; it refers to asexual propagation of the organism in question. For example, many filamentous cyanobacteria undergo vegetative reproduction by fragmentation of the filament; the fragments disperse and carry on growing. In plants, one example of vegetative propagation can be observed in a popular houseplant, the spider plant: the parent plant will send out long shoots bearing miniature “plantlets,” which will begin to root themselves if they come to rest upon the soil. These tiny plants can soon be severed from the parent plant and grow independently—no sexual reproduction required! 

Zooplankton

Microscopic animals found in the plankton of aquatic environments—“in the plankton” means that they are free-floating (not attached to other structures, plants, animals, or surfaces) in the water (suspended within the water rather than resting on the bottom of the waterbody).