by Howard Webb (St. Louis, MO, USA)
Stentors are a unicellular ciliate, noted for their trumpet like shape (hence the name stentor, after the Greek herald of the Trojan war). Stentors are one of the largest single celled organisms, occasionally being several millimeters in length.
Stentors are usually found in the calm water of ponds and lakes, usually near the surface attached to leaves or twigs. While they are capable of free swimming, they are most often noticed clustered together in small colonies. These particular stentors were found in a cluster attached to the side of a collecting jar. I had gathered a few twigs from shallow water (I was actually looking for hydra), and they became apparent after about a week. I used a small pipette to scrape the colony from the side of the jar and transfered it to a slide for observation.
Normally it takes a bit of hunting to find stentors, though I have on occasion found them so thick that a sample is tinged green with their presence.
Most notable of the stentor is the 'crown' of cilia surrounding the trumpet 'bell'. This crown is not a complete circle. These cilia are used to create a current of water from which it sweeps food. Every little while, the stentor will close up the cilia crown and contact, bringing the food within its cell structure.
The crown is not the only cilia on the stentor, its whole body is covered with shorter cilia, which are used for locomotion when free swimming. When moving, the stentor is contracted into an oval or pear shape.
Being single celled, there are no separate parts which make up a "mouth" or other organs. For digestion, the cell wall envelops the food, and separates to form a round bubble like "vacuole" within the cell. After the nutrition from the food is extracted, this vacuole moves to the outer cell wall and 'pops', evacuating the remaining contents. Since stentors have a cell density higher than the water in which they live, osmotic pressure causes water to transport into the cell. The stentor cell actively collects this excess water into a vacuole, and expels it; thereby maintaining the internal fluid density.
Stentors, like most ciliates, are filter feeders; passively eating whatever happens to be swept in their direction. They normally eat bacteria and algae, though large stentors are reported to opportunistically eat rotifers or anything else that they can catch.
Unlike some vorticella, where the whole colony is connected as a single organism, a colony of stentors is a group of individual organisms which just happen to be located together. This colony looked like a spot of mold beginning to form on the side of the collecting bottle. I pushed it loose with a pipette, and transferred it to a microscope slide.
When stentors are traveling, they are not in the typical trumpet shape, but contract into a more oval shape. The cilia on the trumpet bell closes up, and the cilia on the body are used for locomotion. The illuminator was moved down to give more contrast (and also shows up more background artifacts - compare to the next photo).
Another stentor in motion.
Stentors have a rather complex reproductive cycle. Here a stentor undergoing division.
Food vacuole being evacuated.
Movie of the cilia around the bell of the stentor. The bell is more than a simple round shape.
Movie showing water current produced by cilia, and contractile vacuole shrinking.
Depth: collected near the shore, at less than 6 inches depth
Secchi visibility: 2 meters
Location: quarry at Whitecliff Park, Crestwood, MO (lat: 38.5561, long: -90.3688 (NAD83/WGS84)). The park contains an old, abandoned quarry, which is probably one of the deeper bodies of water in the area. The quarry is generally closed to the public, though the city has been kind enough to give me access.
Microscope: Bausch & Lomb monocular, 10x ocular,
4x, 10x and 40x objectives.
Illumination: Luxeon K2 LED
Camera: Canon A540 (6 megapixel)
Software: Photoshop Elements, VirtualDub
Vance Tartar, The Biology of
Stentor, Oxford, New York, Pergammon Press,
This is a classic work. Most of the text describes studies of slicing and dicing stentors, and observing their regeneration; though there is a thorough coverage of their anatomy and behavior, as well as culture techniques.
Comments to the author are welcomed.
Published in the July 2007 edition of Micscape Magazine.
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