Mouvements des diatomees V. Le pivotement polaire spatial de Gomphonema acuminatum Ehrenberg

Abstract

The median polar pivoting in aquatic media of Gomphonema acuminatum Ehrenberg is one of the numerous possible movements achieved by this biraphide diatom. This movement, never described until now, justifies a complete study because the rotations from 90°to 300°in less than two seconds with or without simultaneous sliding along the raphe presents a serious of biomechanics in order to understand the motor functions of diatoms. Video recording of the polar pivoting, frame by frame, at 1/24 second allows a precise analysis and demonstrates die amazing characteristics of this movement. Moreover, tools as graphical cinematical analysis and simplified equations of standard mechanics, enable, on the one hand, testing of the assumptions of Dram and Hopkins (1966) as well as Edgar and Pickett-Heaps (1983) on the movement of diatoms, and on other hand, quantification of the efforts developed during these movements thanks to the knowledge of diatoms density. Both theories are discussed as a function of the problems raised by diatom morphology, die characteristics of this movement and the geometrical dimensions of the support, constituted by the natural sustrata in which the diatom moves. For this movement, Edgar and Pickett-Heaps (1983) hypothesis seems better suited to bio-mechanic observations and particularities.