The rimoportula is a tubular process found in some centric, araphid, and raphid diatoms, through which polysaccharides and other carbon-containing substances are extruded. Rimoportulae are characterized by a lip-shaped aperture on the internal face of the valve. On the external valve face, the opening of the rimoportula may be a simple, round opening or a tube. Rimoportulae are considered to have appeared relatively early in diatom evolutionary history, but have been lost in a number of more advanced, raphid groups. They are found in a number of centric genera, including Stephanodiscus and Aulacoseira, some araphid taxa, including Diatoma, Hannaea, Meridion and Tabellaria, and some eunotiod taxa, such as Actinella, Amphorotia, Eunophora, and Eunotia.
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.
Image Credit: Sarah Spaulding
External view of the rimoportula of Stephanodiscus yellowstonensis.
Image Credit: Marina Potapova
Internal view of the rimoportula of Stephanodiscus yellowstonensis, showing the 'lip like' internal expression.
Image Credit: Paula Furey
Internal view of the rimoportula of Eunotia macroglossa. The rimoportula is positioned at the valve apex, distal to the raphe. Note that the raphe terminates in the helictoglossa.