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**The perforation of the frustules of planktonic diatoms Pseudosolenia calcar-avis and Proboscia alata (Bacillariophyceae)**

*A.O. Kovalevsky Institute of Biology of the Southern Seas of RAS, Sevastopol, Russia*

*Abstract:*

Physiological and biophysical characteristics of microalgae should strongly depend on the surface area of the cover of organisms, as all the material-energy streams flow through the surface. However, to determine the relationship between the intensity of the flow of substances with the physiology of unicellular, it is necessary to take into account only the area of perforations, since the rest of the shell is impermeable for substances. The direct determination of the area of perforations on the entire surface of the microalgae is very difficult. Therefore, the indirect method of estimating the perforation area using geometric modeling of the perforation distribution (texture) on the surface was used in this study. The object of the research is two types of marine plankton diatoms with large cylindrical frustules. It was assumed that the frustules are covered with a regular triangular texture of the areola. This texture can be divided into regular hexagons, which allows us to estimate the number of areolas as the ratio of the surface area of the frustules to the area of one hexagon. The model takes into account that each areola is covered with a silicon plate perforated by a smaller pore. The multiplication of the number of areolas on the area of a given pore gives the value of the total area of perforations. Calculations showed that the perforation of the frustules of *Proboscia alata* was 4%, and *Pseudosolenia calcar-avis* – 6%. These are the first estimates of the perforation of the entire surface of the diatom frustules. The acquired data confirms the hypothesis that frustules of the most centric diatoms are covered by pores by about 5%, and the other surface is impervious to material flows.

*Keywords:*

Phytoplankton, bacillariophyceae, Sea of Azov, biophysics, centric diatoms, material fluxes, area of perforations, stable morphometric trait, surface to volume ratio.

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