Ascomorphella (Hertwigella) volvocicola is a parasitic rotifer that lives inside Volvox-colonies, in this case Volvox aureus. It feeds on the algal cells of the colony, thereby finally killing it. The rotifer, shown here fully stretched, free swimming and partially to fully contracted (Figs. 1 & 2), fled the Volvox-colony immediately after I applied a coverslip, therefore I could not image it inside the Volvox-colony. It turned out to be a really fast swimmer, but finally I managed to reduce the amount of water under the coverslip to such an extent that its swimming speed was significantly slowed down, so that I could take a couple of photos. Also shown is a part of the Volvox-colony with a few surviving algal cells of the already heavily degraded colony, as can be seen by lots of bacteria in the mucilage, an egg of this rotifer and an embryo at two different focal planes (Fig. 3). The fully extended rotifer measures approximately 110 µm in length. All images are at the same scale and were obtained through a 40x objective with DIC illumination.
Images made through a microscope. All subject types.