| Abstract: | 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. From the functional-morphological point of view, three construction principles can be distinguished in the genus Surirella: 1. valves with pennate costal framework, raphe keels and fibulae (Surirella gemma group); 2. frustules where all supporting elements are in the form of corrugations, with raphe keel and fibulae (Pinnatae, Fastuosae, Surirella striatula group); and 3. as in 2, but with true alae with alar canals (Robustae) instead of keels with fibulae. |
