SCALE AND BRISTLE MORPHOLOGY OF MALLOMONAS-TONSURATA (SYNUROPHYCEAE) IN CULTURES WITH VARIED NUTRIENT SUPPLY

Scale-bearing taxa of the chrysophytes are important paleoindicators b ecause of their often restricted ecological requirements and their hig hly preserved extracellular siliceous structures. The diagnostic featu res can usually only be resolved using electron microscopy and, since these features are often shared between closely related taxa, identifi cation in field studies remain uncertain in most cases. As the respect ive influences of genetics and environmental factors upon morphologica l variation cannot be evaluated in field studies, examinations were co nducted by growing a clonal culture of Mallomonos tonsurata in differe nt media with varying silicon, nitrogen and phosphorus supply, followe d by micromorphological analyses of scales and bristles. Increased sil ica content resulted in significant elongation of scales with a corres ponding tendency to build slender scales. In experiments with varied r atios of nitrogen and phosphorus in the media the most pronounced chan ges were observed under phosphorus enrichment leading to significantly larger scales and more needle-like bristle tips. These bristles resem ble those of M. areolata. This shows that bristles are more variable t han scales and thus must be regarded as of little value for taxonomica l description. However, the above-mentioned changes are not sufficient ly pronounced to result in a sharp distinction between two different s pecies. This confirms that siliceous structures of chrysophytes are, i n principle, a most valuable tool for taxonomic differentiation althou gh in field studies morphological variability of taxonomically relevan t characters should still be considered.