MOVEMENTS OF DIATOMS V - THE MEDIAN POLAR PIVOTING OF GOMPHONEMA-ACUMINATUM EHRENHERG

The median polar pivoting in aquatic media of Gomphonema acuminatum Eh renberg is one of the numerous possible movements achieved by this bir aphide diatom. This movement, never described until now, justifies a c omplete study because the rotations from 90 degrees to 300 degrees in less than two seconds, with or without simultaneous sliding along the raphe presents a serious of biomechanics in order to understand the mo tor functions of diatoms. Video recording of the polar pivoting, frame by frame, at 1/24 second allows a precise analysis and demonstrates t he amazing characteristics of this movement. Moreover, tools as graphi cal cinematical analysis and simplified equations of standard mechanic s, enable, on the one hand, testing of the assumptions of Drum Br Hopk ins (1966) as well as Edgar & Pickett-Heaps (1983) on the movement of diatoms, and on other hand, quantification of the efforts developed du ring these movements thanks to the knowledge of diatoms density. Both theories are discussed as a function of the problems raised by diatom morphology, the characteristics of this movement and the geometrical d imensions of the support, constituted by the natural sustrata in which the diatom moves. For this movement, Edgar & Pickett-Heaps (1983) hyp othesis seems better suited to bio-mechanic observations and particula rities.