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Diatoms of the United States is now known as Diatoms of North America.
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Rimmed depression



A tubular process through the valve of some diatoms. On the internal valve face, the rimoportula opening has the shape of a pair of lips. On the external valve face, the rimoportula opening may be a simple, round aperture at the valve surface or it may be a tube extending out from the valve. Plural form is rimoportulae.

Rimoportulae are found in centric genera such as Stephanodiscus and Aulacoseira; in araphid genera such as Diatoma, Hannaea, Meridion and Tabellaria; and in eunotioid genera such as Actinella, Amphorotia, Eunophora, and Eunotia.

Rimoportulae extrude polysaccharides and other carbon compounds. They are considered to have appeared relatively early in diatom evolution, but to have been lost in a number of more advanced, raphid groups.

Alternative Term

labiate process

jelly pore

The term "jelly pore" is used in much of the older literature, including in Patrick and Reimer (1966).


Patrick, R.M. and Reimer, C.W. (1966). The Diatoms of the United States exclusive of Alaska and Hawaii, V. 1. Monographs of the Academy of Natural Sciences of Philadelphia 13.

Round, F.E., Crawford, R.M. and Mann, D.G. (1990). The Diatoms. Biology and Morphology of the Genera. Cambridge University Press, Cambridge, 747 pp.