Euglenids are common, and can be recognized by their prominent flagella (usually 2, sometimes 1) emerging from a pocket at the front of the cell. The forward-pointing flagellum is often quite thick, compared to other flagellates.
In addition, the cell membrane is covered by a pellicle of proteinaceous strips. This pellicle gives the cell a ridged appearance, but can sometimes be hard to see. Cell bodies range from more to less rigid.
Most euglenids can use their flagella to swim, but some have gliding motility as well. The gliding euglenids often point their anterior flagellum in the direction of motion, and keep it largely straight except for the tip, which bends left and right. Aside from motility, the flagellum is also used for sensing and prey-capture.
Although Euglena is photosynthetic, most euglenids are phagotrophic, indicating that the photosynthetic euglenids acquired their ability secondarily.
Prominent thick anterior flagellum, gliding motility, anterior cell body is tapered. Lacking in chloroplasts and hence non-photosynthetic (unlike Euglena). When the cell changed direction in the course of gliding, the cell body deformed from its original rectangular shape.
This cell squirmed a lot, especially when feeding, as can be seen in the animation below. The pellicle is finely ridged, and this is visible in some of the images when viewed at full size. The body contains starch (paramylon) granules.
What appear to be two Peranema cells in the process of pulling apart from each other, their cell bodies squirming and their flagella flailing in the process. They may have been conjugating, or perhaps just finished cellular division.
Euglenid with two flagella easily visible, the anterior-pointing one longer than the posterior-pointing one. Cell body filled with polysaccharide storage granules. However, this individual cell was squirming too much for the identification to be secure.
Cell body oval, with two flagella, both thick. The anterior-pointing flagellum more active than the posterior-pointing flagellum, which is long, relatively straight, and drags behind the cell. It is responsible for the occasional sudden twitching recoil of the cell.
Anisonema cell separation?
I first saw this cell and wondered what could possibly have four flagella, but on closer inspection I realized that it was actually two flagellates, each with two flagella, stuck to each other lengthwise:
The process of separation involved much bodily squirming and beating of flagella, and was video-recorded:
After separation, it was possible to identify the cells as Anisonema:
This unusual euglenid could be called the “durian flagellate”. It has a single thick flagellum emerging from an aperture (see last image above) in a spiky and rigid lorica. Not surprisingly, it does not glide, but instead swims with its flagellum. The inside of the cell is filled with granules which could be paramylon (polysaccharide), like in other euglenids.
The swimming can be quite swift, quickly leaving the observer behind. The flagellum appears to be wound helically backwards around the cell body during swimming. The cell rotates around its axis during swimming. The winding of the flagellum is visible in the following images:
A sense of its speed can be found from this video:
These delightful forms had a peculiar warped shape that reminded me of a well-fried potato chip. These folds and curves are not rigid; I saw some of these changing shape occasionally, but at least one had some difficulty flipping over when wedged between slide and cover-slip.
In some of these pictures, the trailing flagellum, usually thinner and harder to spot than the anterior flagellum, can be seen. Whereas the anterior flagellum moves only at the tip, the trailing flagellum beats in a wave-like motion regularly. Eyespots, vacuoles, and other cytoplasmic inclusions are also indicated. A patterned pellicle can be seen in some images too.
Small gliding euglenids
The smaller euglenids may be Notosolenus (with two flagella) or Petalomonas (with one flagellum), but their small size makes it hard to be sure.