VALVE DEVELOPMENT IN STEPHANODISCUS HANTZSCHII GRUNOW (BACILLARIOPHYCEAE) AND ITS IMPLICATIONS ON SPECIES IDENTIFICATION

Abstract

Clonal isolates of Stephanodiscus hantzschii Grunow were grown in batch culture and growth rates were measured during the exponential growth phase. Clones differing in size grew at significantly different rates at 20°C but not at 12°C. The reduction in cell size (diameter) over a period of time was variable within and among clones at 12°C over the course of one year. Mean concentration of Si/cell (pg Si/cell) was related to mean cell size of the respective clones. Valve morphology in older clones at 12°C and two grown at 20°C showed visual signs of decreased silicification, typical of the morphotype referred to as S. hantzschii fo. tenuis (Hust.) Håkansson & Stoermer. Occluded valve types diagnostic of Pseudo-stephanodiscus perforatus Sieminska (Genkal & Kusmin) appeared at the onset of the exponential growth phase. The rimoportula was the final process to develop during frustule formation. Auxospore development showed conclusively that forms hantzschii, tenuis and P. perforatus are just different phases in the growth cycle of the species S. hantzschii Grunow. An emended description of the species should include all the morphotypes in the life cycle.