Mendota Diatoms

Algae:

"Algae" is a broad term for a wide range of organisms, most of which are aquatic and can photosynthesize, but which lack traditional plant parts like roots and other specialized cells.  There is no concrete definition of algae, and it is used mostly in a general sense.  However, most people agree that a wide range of organisms including diatoms, most single-cell plants, and seaweeds belong in this category.  Many algae are plants, but not all of them.

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Apical axis:

The imaginary line from farthest tip to tip through the valve center; the longest axis of elongated diatoms.  The apical axis most often follows the line of the raphe.

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Areolae:

The individual dots on the face of a diatom; they are pores.  (Singular: areola.)  The areolae may be individual and scattered, or organized into patterned lines called striae.  Areolae may be shaped like dots, dashes, or curved dashes (rarely). If out of focus, areolae that form striae may look like solid lines.

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"cf.":

Taxonomic shorthand for the Latin word "conferatur," which in this context means "looks like."  This represents that the diatom pictured looks like the species named, but that there may be some uncertainty about whether or not that's exactly what it is. 

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Ex: "cf. Navicula tripunctata" means that the diatom is probably of the genus Navicula and looks most like the species tripunctata.  "Navicula cf. tripunctata" means that the diatom is definitely a Navicula, but that the specific species tripunctata is a best estimate.

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Convergent striae:

Striae which tend to point towards the tip of the valve face, as if tilted in line with the apical axis.  In contrast, radiate striae point away from the valve center and away from the apical axis (if present).

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Costae:

Thickened solid "rib" lines on the valve face which are often parallel to striae.  They are not made of areolae.  Some, but not all, go across the entire valve face.

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Cruciform:

Diatoms with a valve shape that looks like a cross or +. 

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Diatom:

Diatoms are a type of algae.  They are single-celled organisms, although many species of diatoms live in grouped colonies.  Diatoms are not plants but they do photosynthesize, and they provide 20-30% of the oxygen we breathe.  Diatoms take silica from their environment and use it to build their outer cell wall out of glass.  Because of this, their shells don't decompose and survive long past the diatom's death.

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Dorsal side/margin:

The side of an asymmetrical biraphid diatom that is wider, more arched, and follows the longer path from tip to tip.  The other side is the ventral side: the two sides are separated by the raphe.  The dorsal margin is the edge of this side.

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Fibulae:

Internal support structures that larger diatoms sometimes have.  (Singular form is fibula.)  In many kinds of diatoms the fibulae may look like thick bands that stretch from the raphe to the valve margin. Fibulae are also present in the raphe systems of Nitzschioid diatoms, and look like the rail road ties of train tracks.

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Frustule:

The glass outer shell of a diatom which protects its internal organelles while allowing photosynthesis to still occur.  When diatoms are processed for identification, like in this website's photos, the frustule is the only part of the diatom that remains.

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Genus:

The identification group above "species" used in taxonomy.  (Plural form is "genera".)  Species within a genus share a set unique physical characteristics that define which species belong in the genus.

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The genus name is the first of the two words in a species' scientific name, and is capitalized.  Ex: for Amphora ovalis, "Amphora" is the genus name.

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Girdle view:

The viewpoint of a diatom which shows the "side" of the diatom, in contrast to "valve view," which shows the valve face.

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Heteropolar:

Having differently-shaped poles, or tips, at each end of the diatom.  This trait makes the diatom asymmetrical.  The wider end is known as the headpole, and the narrower end is called the footpole.

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Ornamentation:

Any bumps, dimples, lines, patterns, or other "designs" on a diatom's surface that are not the raphe.

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Radiate striae:

Striae that point away from the diatom's center.  Most centric diatoms exhibit this trait, but many raphid diatoms also have radiate striae.  Striae can also be parallel to the transapical axis or "convergent," meaning they point towards the diatom's tips, perpendicular to the direction of radiate striae.

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Raphe:

The long thin crevice which acts as the movement system of diatoms, allowing the cell to inch through mud or across surfaces by contracting and stretching.  The raphe is often located along the apical axis of the valve faces, but may also be located along the perimeter of the valve margin, irregularly placed, or on only one valve face (monoraphids). 

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When a raphe system is positioned along the apical axis, it commonly looks like the heads of two bobby pins pointing at each other.  When positioned along the valve margin, it often looks like blurry train tracks.

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Sigmoid:

Shaped like an "S".  Some sigmoid diatoms are still considered to be bilaterally symmetrical, if one side is simply a reversed mirror image of the other side.

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Striae:

Patterned lines made up of areolae in rows on the valve face.  Individual areolae within a stria may or may not be visible with a light microscope.  Striae can be made up of more than one row of closely grouped areolae: striae made up of a single row are uniseriate, those made of two rows are biseriate, and those made up of more than one row are multiseriate. 

 

The position, direction, and number of striae within a certain distance on a diatom are often used to as measurements to identify the species of the diatom.

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Transapical axis:

The imaginary straight line which goes through the center of a diatom and is perpendicular to the apical axis.  This line is sometimes used to determine the symmetry of a diatom or the direction of its striae.

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"µm":

Stands for "micrometers,"or "microns" for short.  1 µm is equal to one millionth of a meter.  Microns are the best unit of distance to measure diatoms by: diatom sizes tend to range anywhere from 5-300 µm. 

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Undulate:

Wavy or expanding/contracting shape.  This may apply to the outline of a valve's shape, the up-down waves across a valve face, or to any of the internal or external lines on a frustule.

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Uniserate/Biserate:

See: "Striae."

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Valve face:

The "top" and "bottom" sides of a diatom frustule, which are most commonly seen: it may contain features like ornamentation, raphe, or spines, and is the side of the diatom that connects to other diatoms.  The valve margin is the edge/perimeter of the valve face.

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Valve view: 

The viewpoint of a diatom which shows its valve face, in contrast to "girdle view," which shows the valve's side.

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Ventral side/margin:

The side of an asymmetrical biraphid diatom that is thinner, flatter, and follows the straightest path from tip to tip.  The other side is the dorsal side: the two are separated by the raphe.  The ventral margin is the edge of this side.

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