VALVE MORPHOGENESIS IN AN ARAPHID DIATOM SYNEDRA ACUS SUBSP. RADIANS

Abstract

Valve morphogenesis stages in the araphid Synedra acus subsp. radians (Kütz.) Skabitch. were studied using of the light, fluorescent and electron microscopes. The most interesting and complete results were obtained with transmission electron microscope (TEM). Morphogenesis begins by the formation of a thin silica strand (sternum) with little branches (future virgae). Virgae begin to grow as semi-transparent siliceous branches which often consist of two parts. Later, the distance between growing virgae are fuse by wimines from the sternum to the edge of valve and then areolae are formed into striae. The rimoportula and apical pore field start to form at an early stage of valve formation. In the beginning, the forming rimoportula looks like a loop of silica filament which often substitutes for an areola of the apical areola row. After the mantle begins to form, apical pore fields start to grow as series of small spines which subsequently evolve into ribs separating rows of porae. At the end of morphogenesis, the valve becomes thicker and attains the mature size and outline.