Abstract
The valvar structure and the cingulum arrangement of a diatom related to the Gomphoneis herculeana – Gomphoneis minuta complex were investigated in electron and light microscopy. Ultrastructural features include striae composed of double rows of areolae, apical pore fields composed of pores structurally differentiated from the areolae and the presence of an axial siliceous plate responsible for longitudinal lines visible in light microscopy. The pars interior of the valvocopula looks like a marginal lamina of silica. A new model of organization for the cingulum, quite different from the classical model, is proposed. The valvocopula is a closed band with a connective septum at both the head and the footpole. The copulae, each of them with a connective septum, are open bands, with their openings at opposite poles. All septa possess on the advalvar face a projecting lamina that fits under the pseudosepta of the valve or the septum of a girdle band. The first two copulae are directly connected with the opposite septa of the valvocopula. The third copula is attached to the first copula and the fourth to the second. Key words: Bacillariophyta, Gomphoneis, valve, model, cingulum.
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