Visit us at

Diatoms of the United States is now known as Diatoms of North America.
This site has been redesigned and updated, and will be closing soon.

Axial costa



Axial plate

A narrow ridge of silica along the axial area on the inside of the valve bordering the raphe.

Mastogloia smithii is an example with two internal axial costae. Together they form the sides of a groove, or gutter (Paddock and Kemp, 1990), widening slightly at the central nodule and stopping short of the distal raphe ends.

See also costa.

Alternative Term

longitudinal rib

Similar to an axial costa, but in general more rounded and relatively wider. Found in the genus Frustulia for example.


Krammer, K. and Lange-Bertalot, H. (2000). Bacillariophyceae 5. English and French translation of the keys. In: Büdel, B., Gärtner, G., Krienitz, L. & Lokhorst, G. M. (eds.). Süßwasserflora von Mitteleuropa. 2(5), 311 pp. Spektrum Akademischer Verlag, Heidelberg-Berlin.

Lee S.S., Gaiser E.E., Van de Vijver, B., Edlund, M.B., and Spaulding, S.A. (2014). Morphology and typification of Mastogloia smithii and M. lacustris, with descriptions of two new species from the Florida Everglades and the Caribbean region. Diatom Research. doi:10.1080/0269249X.2014.889038

Paddock, T.B.B. and Kemp, K.D. (1990). An illustrated survey of the morphological features of the diatom genus Mastogloia. Diatom Research 5: 73-103.

Ross, R., Cox, E.J., Karayeva, N.I., Mann, D.G., Paddock, T.B.B., Simonsen, R. and Sims, P.A. (1979). An amended terminology for the siliceous components of the diatom cell. Nova Hedwigia, Beihefte 64: 513-533.