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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 "f"


A hyaline area of thickened silica extending from the central area of some pennate diatoms. A transverse fascia is formed by secondary deposition of silica into depressions on the valve. Examples of genera having a transverse fascia include Luticola and Staurophora. Plural form is fasciae.

See also stauros for a similar structure.


Series, or bundle, of rows of areolae oriented radially in some centric diatoms.

Fibula - keel puncta

Internal strut that provides structural support to the canal that contains the raphe. Plural form is fibulae. The fibulae extend transapically from the raphe canal to the valve face. Examples of genera having fibulae include Denticula, Nitzschia, and Surirella. From Latin for clasp, pin, or brooch.



Having the shape of a thread.


The narrower apex, or pole, of a clavate valve. Often has a pore field. Example genera include Didymosphenia, Gomphoneis, and Gomphonema.



The large opening in one wall of a loculate areola. Located on the external or internal wall of the areola, depending on species, opposite the velum. Plural form is foramina.


The siliceous parts of the diatom cell wall. Composed of the larger epitheca and the smaller hypotheca. The epitheca overlaps the hypotheca similar to a pill box or Petri dish. From Latin for a little piece.

See also valve and cingulum.

Fultoportula - strutted process

A tubular process through the valve of some centric diatoms. The fultoportula consists of a central tubular process surrounded by two or more satellite pores. Externally, the fultoportula appears as either a tube or a simple pore in the valve wall. The plural form is fultoportulae.

Usually associated with the secretion of β-chitin to maintain buoyancy in the plankton.



Having the shape of a spindle. Broadest at the middle and tapering at both apices.