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These short movies illustrate locomotion and feeding behavior of a Bdelloid rotifer in the context of an urban environment sampling site. Rotifer locomotion by head to toe movement and by corona action are clearly seen. The corona establishes strong vortex currents to draw food into its mouth, and green algae are clearly seen being drawn into the mouth. Digestive movements of mastax and stomach are shown.
This rotifer is from leaf litter accumulated in a discarded plastic box which was then submerged in rain water. The sample was harvested by drawing superficial material into a Pasteur pipette and this was transported to the laboratory in an Eppendorf tube. Approximately 50 µl were transferred to a microscope slide as one drop and a cover slip applied. This slide was viewed with a conventional bright-field microscope and a Pupil Cam attachment (Ken-A-Vision, Kansas City, MO). The Pupil Cam is a simple and inexpensive device for making appealing materials easily visible for biology classes. Focusing up and down through the plane of focus was used to allow viewers to form an impression of thick structures.
Bdelloid rotifers are microscopic animals that are common in freshwater ponds, puddles, and films of water (4). They are conspicuous in field samples and have been known almost as long as microscopes have been available (1). Their two distinguishing characteristics are the ability to withstand the periodic dehydration experienced in their ephemeral environments by a specialized process called anhydrobiosis (3) and the absence of sexual reproduction (5).
Rotifers feed by creating strong currents of water using rings of cilia that make up the corona organ. These currents blow plankton through the mouth and into the mastax organ. The mastax is a muscular organ lined with hard chitinized trophi (2) that resemble jaws. The mastax opens and closes in a pulsing manner and the hard trophi crush food passing from the mouth to the stomach. The stomach is usually the most conspicuous part because it contains many pigmented cells ingested by rotifers, such as green algae (4). Rotifers may move across surfaces by a head to toe movement or through open water using the corona in order to find favorable feeding places.
References.
1. Hartog, M. 1896. Rotifera, Gastrotricha, and Kinorhyncha, p. 197–240. In S. F. Harmer and A. E. Shipley (ed.), The Cambridge natural history, vol. 2. McMillan, New York, NY.
2. Klusemann, J., W. Kleinow, and W. Peters. 1990. The hard parts (trophi) of the rotifer mastax do contain chitin: evidence from studies on Brachionus plicatilis. Histochem. Cell Biol. 3:277–283.
3. Ricci, C. 1998. Anhydrobiotic capabilities of bdelloid rotifers. Hydrobiologia 387/388:321–326.
4. Ricci, C., and G. Melone. 2004. Key to the identification of the genera of bdelloid rotifers. Hydrobiologia 418:73–80.
5. Welch, J. L. M., D. B. M. Welch, and M. Meselson. 2004. Cytogenic evidence for asexual evolution of bdelloid rotifers. Proc. Natl. Acad. Sci. USA 101:1618–1621.
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