The structure of the frustule ofAttheya decorawest (bacillariophyceae, biddulphiineae) with special reference to the organic compounds

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Abstract
With the exception of the equatorial region under the thecal junction and within the horns, the protoplast of each half cell of Attheya decora is covered with an inner, non-silicified (polysaccharide) wall layer. The protoplast is retracted from the siliceous elements of the valve (but not around the labiate process and only slightly so within the horns) and in the four lateral regions under the bases of the horns, the organic inner wall layer fuses with the silicified basal layer of the valve which is completely separate from the valve proper. The pars interior of the open intercalary bands and of the connecting band has a boundary of small, long, slender teeth. It continues as a thin visor-shaped, polysaccharide “continuatum taeniae” at both flanks. These continuations fuse with the polysaccharide inner wall layer where it covers the retracted protoplast in the region of the intercalary bands. That these unique structures may help to understand the structure of “normal” frustules is discussed.