THE SPINES OF THE CENTRIC DIATOM CORETHRON CRIOPHILUM - LIGHT-MICROSCOPY OF VEGETATIVE CELL-DIVISION

As part of a study of the biology of the marine planktonic centric dia tom Corethron criophilum, cells have been followed through the vegetat ive cell cycle from immediately before cytokinesis until separation of the two daughter cells. After cytoplasmic cleavage, which lasts 30 mi n, each of the daughter cells becomes shorter and leaves space for the spines to develop on each of the new hypovalves. The relationship of the two cingula of each cell remains static for approximately 12 h whi le the new valves are developed. Expansion of both of the daughter cel ls in the pervalvar axis then withdraws the girdles from one another t hus revealing the mature spines of the new hypovalves which now spring out to assume their final positions. The function of the cingulum in protecting and releasing the spines in this diatom is discussed.