Distigma gracile

Length of the body 30-36 microns and breadth 7-8 microns. Body, when swimming rapidly, like a long carrot, rounded at the front, slowly narrowing towards the back end which thins gradually but is not pointed. Body rather slender, hence the specific name. The cell is nearly always curved to and fro, but not regularly as in a cork-screw. The little thickened anterior end is slightly notched in the middle at the point of insertion of the flagellum. Although the pellicle appears delicate, metaboly is not excessive. The posterior end may show a small button-shaped dilation, but this is not large enough to give rise to a spherical thickening of the whole cell or a major part of it. It often happens that the posterior part of the body or even almost the entire cell becomes cylindrical, while the spiral curvature mostly persists. Stronger contractions are only undergone when there is considerable disturbance. Changes of shape may also appear during swimming, but only in the form of curvatures and limited torsions. The longer flagellum is about as long as the body. The short flagellum is very short, about as long as half the breadth of the anterior end, i.e. about 3-4 microns long. It is slightly curved and bent to one side. Nucleus in the middle of the cell. Paramylon grains rather characteristic, never present in large numbers, so that they are not in contact with one another. They are very minute in the narrow posterior part. Even the largest ones in the anterior part are rather small.