Freshwater Algae: Motile algae. Introductory text with photomicrographs.

Algae.
Motile Algae (unicells).

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Algae: Intro.

Colonial

Motile Unicellular Algae.

The two motile algae presented in this gallery are Euglena and Trachelomonas, both members of the phylum Euglenaphyta. They are important in the food chain of the freshwater habitats, providing nutrition for a wide variety of micro organisms and filter feeders such as water fleas.
The motile alga Chlorella (not pictured here) is important for the same reasons, as well as its propensity for establishing symbiotic relationships with many protozoa and more complex creatures such as Hydra viridis.

Many of the motile algae, such as Euglena, store their carbohydrate energy reserves in the form of refractile granules of the glucose polymer paramylum (or paramylon). These granules are called pyrenoids.

Euglena.

	This large Euglena shows all of the features typical of the Euglenaphyta except the prominent flagellum which is difficult to see in brightfield illumination. The eyespot, which contains the animal pigment astaxanthin is clearly seen. The large transparent granules are pyrenoids. Brightfield, x850.
	These two euglenoids are photographed in a mass of mucilage in which many hundreds of similar organisms were also embedded, and as such, members of one of the colonial varieties which have this form. Interestingly, each of the individuals is capable of making its way out of the containing matrix, undergoing elongation and living an independent existence as a free-swimming Euglena. Brightfield, x850.
	Another two Euglenoids embedded in organic matter. Darkfield. x600.
	A single inactive euglenoid against a background of fragments of a discarded crustacean exoskeleton. The colours are due to the chromatic aberration effects of a darkfield produced by a stopped Abbe condenser and small lamp diaphragm aperture. This picture was used on the dustjacket of the UK (1987) edition of Margulis and Sagan's excellent book "Microcosmos" -- a highly recommended read. Darkfield. x600.

Trachelomonas.

	A single Trachelomonas against a background of filamentous algae. The distinguishing feature of Trachelomonas is the oval lorica (or pot) which encases an organism having very similar features to Euglena. The lorica has a small hole at the narrow end through which the single flagellum extends. There are usually surface papillae, and the lorica over time becomes first yellow, then increasingly brown-coloured due to absorption of iron from the water. Here is a diagram of Trachelomonas. Darkfield, x600.
	Another lone Trachelomonas showing papillae on the lorica clearly. The white out-of-focus objects in the background are the scavenging protozoan Coleps. Darkfield, x400.
	Two Trachelomonas. The nature of the chloroplast is clearly seen in these pictures, and a suggestion of the euglenoid eyespot can be seen in the specimen on the left. About a third of the original transparency was scanned to give the high magnification of this picture. Brightfield, x2000.