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Stria density and count in centric diatoms




Stria density is based on the number of striae in an arc of circumference. The density = total number of striae on the valve * 10 / circumference. In Figure 1, the stria density is equal to (21) (10) / 54.3 µm, or 3.9 striae in 10 µm of circumference.

Stria count is based on the number of striae in a chord of the valve face. In Figure 2, the chord crosses 5 striae, giving a count of 5 in 10 µm.


Anonymous. (1975). Proposals for standardization of diatom terminology and diagnoses. Nova Hedwigia, Beihefte 53: 323-354.

Collins, G.B. and Groetsch, C.W. (1981). An elementary mathematical problem arising in diatom taxonomy. International Journal of Mathematical Education in Science and Technology 12(1): 121-124.

Genkal, S.L. (1977). On counting of some taxonomically significant structural elements of valves in the diatom algae of the family Thalassiosiraceae Lebour emend. Hasle (Bacillariophyta). Botan. Zhurnal 62(6): 848-851.

Theriot, E. (1988). An empirically based model of variation in rotational elements in centric diatoms with comments in ratios in phycology. Journal of Phycology 24(3): 400-407.