Cephalodella sp. Anatomy and Behavior

Introduction

This is a field sample of the monogonate rotifer Cephalodella sp. that shows several behavioral features including crawling and swimming motion, and bowing and sweeping behavior for ingestion of biofilm material. Rarely observed features such as buccal cilia around the mouth and muscle bands are also shown using slow motion video recording.

Cephalodella is a rotifer of the poorly defined family Notommatidae (3). Their preferred environment is a solid substrate (5) and maximum abundance for most species is neutral or acidic freshwater (1), consistent with harvest of this specimen in New Jersey where freshwater is usually slightly acidic (2).

Methods

Water that had accumulated in a plastic container was collected using a Pasteur pipette to draw material from the surface of submerged leaf litter, then transported to the laboratory in an Eppendorf tube. Approximately 50 µl of water were dropped onto a microscope slide and a cover slip was applied. This was examined using conventional bright-field microscopy. When Cephalodella was located, its motion was recorded using a Pupil Cam attachment (Ken-A-Vision, Kansas City, MO). Cephalodella moves very rapidly making focus and manipulation of stage direction extremely difficult. This was overcome by use of slow motion. Focus was also difficult when two organisms were present in the same field of view; however these images were retained to allow a comparison of size between Cephalodella and protozoa or cyanobacteria.

Discussion

Rotifers are microscopic animals commonly seen in freshwater samples. They have several conspicuous anatomical features which are easily identified after viewing the movie. Their motion is by crawling with the aid of a well developed foot and toe (7). The movement of the foot organ is achieved with bands of muscle that are sometimes briefly visible when they enter a single plane of focus. Swimming is achieved with anterior cilia that are usually difficult to see with the light microscope, but are shown here in silhouette. Food is obtained by bowing and sweeping motions reminiscent of a man using his beard as a brush. Small particles are drawn into the stomach by buccal cilia and a vacuum action of the mastax (7). The mastax is a muscular chamber lined with hard chitinized trophi (4) that are hinged and flex back and forth, resembling jaws. The mastax opens and closes in a pulsing manner and the hard trophi crush food passing from the mouth to the stomach. Many rotifers feed by ingestion of plankton but this animal is adapted to grazing on the microbes attached to a microbial film, a common strategy for microbes living on hard substrates (6) such as inorganic particles or macroscopic algae.

References

1. Berzi, B., and B. Pejler. 1987. Rotifer occurrence in relation to pH. Hydrobiologia 147(1):107–116.

2. Forman, R. T. T. 1998. Pine Barrens ecosystem and landscape. Rutgers University Press, Piscataway, NJ.

3. Jersabek, C. D. 2002. A case of considerable confusion in rotifer taxonomy: the Cephalodella crassipes complex. Archiv für Hydrobiologie 139(2):265–274.

4. 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

5. Pejler, B., and B. Berzi. 1993. On the ecology of Cephalodella. Hydrobiologia 259(2):125–128.

6. Railkin, A. I. 1998. The pattern of recovery of disturbed microbial communities inhabiting hard substrates. Hydrobiologia 385(1-3):47–57.

7. Wallace, R. L., and T. W. Snell. 2001. Phylum rotifera, p. 195–248. In J. H. Thorp and A. P. Covic (ed.), Ecology and classification of North American freshwater invertebrates, 2nd ed. Academic Press, New York, NY.

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