Phenotypic variation of life-cycle stages in clones of three similar Cyclotella species after induced auxospore production

Auxospore production was induced in clonal cultures of three morphologicall y similar Cyclotella species, C. meneghiniana, C. gamma and C. quillensis t o determine the pattern of variation of the frustule morphology through the life-cycle. Investigations were made by light and electron microscopy. The Cyclotella species have in common the tangential undulation of the smooth central area, striated marginal area, presence of valve face and mantle ful toportulae with three satellite pores and at least one rimoportula. Each of the three species produced two size groups with slightly different valve m orphology. The morphological characters of the two size groups can cause id entification difficulties, especially when found together. This paper presents an interspecific comparison of the morphology of the si liceous cell wall of the initial cells and their descendants. Auxospore pro duction was induced in a small portion of the cells 3-12 days after transfe r into seawater based saline medium (7.5 parts per thousand). The initial c ells showed species-specific structures and have taxonomic potential in del imitation of the Cyclotella taxa. Initial cell valves were hemispherical or domed, but cells with a relatively flat central area were found, complicat ing identification. The complex morphology of initial cells found in this i nvestigation has shown that C. wulfiae is the initial cell of C. meneghinia na.