this weekend I found the nice Euglena acus in a sample from my favorite hunting ground. Microscopy is a little bit like playing detective - you find something, document it, identify it and try to understand out more about your find.
The Euglenoids are a fairly old family of species and do not belong to the Algae (although some botanists treat them as such). Originally they were pure heterotroph, eating bacteria. The explanation for the genesis of green phototrophic Euglenoids is that an Euglenoid acquired the plastid by feeding on a green algae and the Chloroplast of the algae has become an organelle subsequently. Sexual reproduction is unknown for all Euglenoids. The most well known family among the Euglenoids is Euglena of which Euglena acus is shown here.
Euglena has only one visible flagella that emerges from a pocket (picture 1). Inside this pocket there is a secondary flagella but it is to short to emerge outside and not visible with light microscopy. To store carbohydrates Euglenoids use so called paramylon granules. The shape of those is characteristic and helps to identify the species (pictures 3 and 4). A common characteristic of all Euglenoids is the striped pellicle - a flexible skin rather than the cellulose cell wall of green algae (pictures 5-7).
Under the flagella pocket is the stigma. Opposite is the photoreceptor that controls the movement of the flagella. It allows Euglena to move towards the light or in case of to much light away from it. Between the stigma and the chloroplast there is a contractile vacuole that is rather active.
Picture 1: 40x, DIC, Euglena acus with flagella
Picture 2: 40x, DIC, Euglena acus meeting with Phacus sp.
Picture 3: 63x, DIC, Euglena acus with paramylon granules
Picture 4: 63x, Phasecontrast, Euglena acus with paramylon granules
Picture 5: 63x pellicle of another Euglenoid
Picture 6: 63x, DIC, dead Euglena acus with striped pellicle and paramylon granules
Picture 7: crop of another Euglenoid with striped pellicle
Regards,
Eckhard
