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FUNCTIONAL VALVE MORPHOLOGY IN SOME SURIRELLA SPECIES (BACILLARIOPHYCEAE) AND A COMPARISON WITH THE NAVICULACEAE 1

On the basis of results of stratigraphic and comparative morphological studies on the diatom frustule, the Surirellaceae is generally assumed to be the endpoint of the evolution of the Pennales. The present study shows that a line of development, based on frustule construction and which parallels the search for optimum design of comparable elements in engineering, can be traced from the Naviculaceae to the Surirellaceae. In both cases lightweight construction is achieved through economy of material and energy expenditure. This leads to structural stability and in the case of the diatom valve, a larger area for metabolic exchange.