Habrotrocha elusa; four details of the head while whirling, different focus planes from dorsal to ventral. Upper left image: focus plane is on the distal end of the dorsal antenna which has two tips. In the lower part of the image the granulated surface of the trunk is visible. Upper right image: focus plane on the characteristic upper lip which is triangle-shaped and is separated from the proximal part of the head by a transversal notch (arrowheads). The asterisk marks the cilia of the rostrum which is as broad as the head width. Lower left image: focus plane on the upper lip which has a characteristic indentation at the tip (arrowhead). Lower right image: focus plane on the mastax / trophi, but also showing the narrow space between the two trochal columns. (2)