Glossary
Like the rest of this website, the glossary is a work in progress. If we’ve missed a term, please contact us to let us know the term and references.
Alveolus
An alveolus is an elongated chamber extending from the axial or central part of the valve toward the margin and forming all or part of a stria. Openings vary widely among genera. SEM is needed to distinguish most features. From Latin for small cavity. Plural is alveoli.
Examples:
* alveolus forms the whole stria (Pinnularia, Caloneis)
* alveolus forms part of the stria (some Mastogloia, Cyclostephanos)
* internal openings are foramina (Pinnularia, Ardissonea, Cyclostephanos)
* internal openings are smaller pores (some Mastogloia)
* external openings are single pores (some Mastogloia, Ardissonea)
* external openings are plates of fine pores (Pinnularia)
This adapted version of Ross et al. 1979 p. 527 is used because so much has yet to be learned about this structure. Authors use variations of this definition so it might be best to consult their papers when using this term.
Alveoli may be difficult to distinguish from loculi. A loculus and an alveolus are both chambered openings in the valve wall but typically only the alveolus is transversely, or transapically, elongated. Images can be a guide.
As with other glossary terms, alveolus describes structures that are physically similar, but may not be homologous (derived from a common ancestor).
See also areola, loculus, and stria.
Citations
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Publication Link: 10.1111/j.1529-8817.2011.01081.x
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Publication Link: 10.1515/bot-2023-0039
Image Credit: S. Spaulding
Image Credit: Tom Frankovich, Mike Sullivan, Matt Ashworth
Image Credit: Stephen Main
Image Credit: Chris Lobban
Image Credit: S. Spaulding
External view of distal end of a Pinnularia valve (SEM) with alveolate striae. Each stria is composed of an alveolus covered by a plate of many fine pores.
Image Credit: Tom Frankovich, Mike Sullivan, Matt Ashworth
Internal view of apex of Ardissonea valve (SEM). Arrow #3 shows an alveolus with a foramen as the internal opening; #4 shows one of the small pores providing the internal openings to other alveoli of the valve.
Image Credit: Stephen Main
Internal view of edge of Cyclostephanos dubius valve with alveoli at ends of the striae (SEM). Foramina form the internal openings and small pores form the external openings. Scale bar = 1 µm.
Image Credit: Chris Lobban
External oblique view of Mastogloia floridensis (SEM). Single pore alveolar openings form a row along the margin and rows on each side of the raphe. An example of alveolate striae with two alveoli on each stria. Scale bar = 10 µm.