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Euglenoids

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[Euglena] (sewage pond), X640.

[Euglena] (sewage pond), X640.

Euglenoids have green chloroplasts, but they are not green algae. Rather, several lines of evidence indicate that they obtained their green chloroplasts by engulfing a green alga sometime in the ancient past. Unlike green algae, they no longer store starch inside their chloroplasts, but instead accumulate paramylon granules in their cytoplasm.

The most distinctive feature uniting euglenoids is their remarkable cell wall. This is known as a pellicle, and is made of proteinaceous strips, which in many species is able to flex and allow the cell to change shape. A large red eyespot located at the cell anterior, and involved in light sensing, is another common feature. Many species possess a single flagellum that originates in a pouch-like reservoir near the eyespot, passing through a canal to the exterior of the cell. Thus, euglenoids commonly possess more than one means of movement.

Apart from the well-known Euglena, the group includes Phacus, with a more rigid cell wall and characteristic discs of paramylon in the cell centre, and Trachelomonas, the Euglena-like cell of which is concealed inside a mineralised wall called a lorica. The flexible cell can often be seen moving inside the lorica.