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Diatoms of the United States is now known as Diatoms of North America.
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Glossary terms starting with "l"


A space or gap in the apical silica of the partectal ring, between the apex and the subapical projections on the sides of the ring. May have a pyriform shape (have the shape of a pear).

Specific to the genus Mastogloia. Visible with SEM; usually not discernable with LM. From Latin for gap. Plural form is lacunae. An example species having a lacuna is Mastogloia calcarea.


A valve having an elongated outline, widest at the middle and tapering to both ends. Width may range from wide to narrow.

Lateral sternum

A thickened area of silica without pores on the valve face parallel to the sternum and interrupting the striae. One on each side of the sternum connected at the central node, giving the whole structure a lyrate shape (shape of a lyre). A freshwater example occurs in Mastogloia pumila.



A silica projection on a split ring girdle band. The ligula of a younger girdle band fills, or nearly fills, the gap caused by the split in the older band next to it. Found in many diatom taxa. From Latin for strap. Plural form is ligulae.


An areola that is elongated in the apical direction. From Latin for little line. Plural form is lineolae.

Lineolae compose the striae of the genus Navicula sensu stricto, or the Lineolate section of Navicula. This type of stria is called a lineolate stria.

Linking spines

In the genus Aulacoseira, linking spines join frustules together in a chain, or filament.

See also separation spines.


The acronym for light microscope. The study of diatoms relies on a compound light microscope in which a beam of light passes through optical lenses to view an image of the specimen. The light microscope provides images of the transparent features of the diatom.

Contributors to the Diatoms of the United States project use research grade light microscopes with the minimum specifications of a 100x, 1.3 numerical aperature (NA) oil immersion objective lens and 1.3 NA condenser lens.

The scanning electron microscope (SEM) is also important in diatom studies.



Having a locule, or chamber. A loculate areola is made of a chamber with a velum and a foramen for two of its walls. A loculate valve has loculate areolae. From Latin for small space.

Example genera with loculate areolae include Diploneis, Muelleria and Neidium.

Longitudinal canal

A chamber having the shape of a tube inside the valve, oriented along the apical axis. It occurs in genera such as Neidium and Muelleria, which have valves consisting of two layers of silica with the canal lying between them. The canals appear as longitudinal lines and may be central or marginal.

Longitudinal rib

A solid silica structure that runs along each side of the raphe in genera such as Frustulia.


A structure having the shape of a crescent moon. Applies to a thickened silica shape in the central area of certain species of Caloneis.