Vegetative cells with a cup-shaped chloroplast containing one pyrenoid; a large anterior eyespot; two cilia of equal length with two contractile vacuoles at their base.
When its size becomes too small, a dividing diatom cell produces an auxospore to expand its cell size back to that which is normal for vegetative cells.
Under non-limiting nutritional environmental conditions, its filaments are composed of photosynthetic vegetative cells; upon nutrient limitation, some of these cells undergo differentiation into heterocysts, akinetes or hormogonia.