Cribrum

A cribrum is a siliceous occlusion (Cox 2004, p. 35) with reticulate (resembling a network) or regular pores (Ross et al. 1979, p. 528). Pores are usually more than 30 nm in diameter (Cox 2004, p. 35). The plural is cribra. A cribrum may be attached to the areola at several points (Cox 2004, p. 35) or by its entire periphery.

In some genera, cribra are visible with light microscopy but they usually require electron microscopy. A cribrum may be combined with a hymen (Diploneis) or with a vola (Petroneis). Cribra may be flat (Achnanthes) or domed (characteristic of Thalassiosirales such as Stephanodiscus).

See also hymen, vola, and occlusion, which are all terms for covering.

Alternative Terms

sieve plate
velum

Citations

Anonymous (1975) Proposals for standardization of diatom terminology and diagnoses Nova Hedwigia, Beihefte 53: 323-354
Cox, E.J. (2004) Pore occlusions in raphid diatoms - a reassessment of their structure and terminology, with particular reference to members of the Cymbellales. Diatom 20: 33-46.

Publication Link: 10.11464/diatom1985.20.0_33
Cox, E.J. (2012) Ontogeny, homology, and terminology - wall morphogenesis as an aid to character recognition and character state definition for pennate diatom systematics Journal of Phycology 48: 1–31

Publication Link: 10.1111/j.1529-8817.2011.01081.x
Idei M., Sato S. and Mann D.G. (2020) The Amazing World of Diatoms. Sogensha Publishers, Osaka, Japan, pp. 176.
Ross, R. and Sims, P. (1972) The fine structure of the frustule in centric diatoms: a suggested terminology British Phycological Journal 7: 139-163
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
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.

Plagiogramma - reticulate cribra — External view of areolae of *Plagiogramma* (SEM) occluded by cribra of silica plates perforated by elongated pores forming reticulations (networks). The cribra are attached to the walls at multiple points. Scale bar = 0.5 µm.

Achnanthes - poroid cribra — External view areolae of *Achnanthes* (SEM) occluded by cribra of silica plates perforated by round pores. The cribra are attached to the walls at multiple points. Scale bar = 1 µm.

Stephanodiscus Domed Cribra — Internal view of *Stephanodiscus* valve showing rows of areolae covered with domed cribra (SEM). Arrow designates a single areola. Fultoportulae are also visible.

Yellowstone Vcd 026 — View of valve interior of *Stephanodiscus yellowstonensis* showing areolae occluded by domed cribra (SEM). Note that the cribra are attached by their entire periphery. Diameter of pores ~ 16 nm. Scale bar = 1 µm.

Petroneis monilifera verdronken zwarte polder23 1 — Outside of a valve of the raphid *Petroneis monilifera* showing areolae occluded by cribra (SEM). Each cribrum is attached to the areola at several points which are the ends of the ribs. (In this genus, a vola is attached to the inside of the cribrum.) Scale bar = 0.5 µm.

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Image Credit: Shinya Sato and Masahiko Idei

External view of areolae of Plagiogramma (SEM) occluded by cribra of silica plates perforated by elongated pores forming reticulations (networks). The cribra are attached to the walls at multiple points. Scale bar = 0.5 µm.

Image Credit: Shinya Sato and Masahiko Idei

External view areolae of Achnanthes (SEM) occluded by cribra of silica plates perforated by round pores. The cribra are attached to the walls at multiple points. Scale bar = 1 µm.

Image Credit: Sarah Spaulding

Internal view of Stephanodiscus valve showing rows of areolae covered with domed cribra (SEM). Arrow designates a single areola. Fultoportulae are also visible.

Image Credit: Sarah Spaulding

View of valve interior of Stephanodiscus yellowstonensis showing areolae occluded by domed cribra (SEM). Note that the cribra are attached by their entire periphery. Diameter of pores ~ 16 nm. Scale bar = 1 µm.

Image Credit: René van Wezel/Rijkswaterstaat, Creative Commons

Outside of a valve of the raphid Petroneis monilifera showing areolae occluded by cribra (SEM). Each cribrum is attached to the areola at several points which are the ends of the ribs. (In this genus, a vola is attached to the inside of the cribrum.) Scale bar = 0.5 µm.