Domain Eukaryota
Euglenozoa

The Euglenozoa are a large kingdom of the Excavata. They include many common free-living freshwater organisms.

They characteristically have two flagella, a long one at the front tip and shorter one next to it.

The Euglenozoa flagella have latticed/tubular support rods and are attached to three microtubule groups that cover the cell. The cytostome (mouth) is near the bases of the flagella.

The Euglenozoa feed on bacteria and small organic material or by absorption. Some have green chloroplasts and produce food by photosynthesis (these have light-sensitive 'eyespots' but no mouths). All have mitochondria and reproduce exclusively by cell division. The three main groups are:

• The Euglenida, in which the microtubule groups are spread into a pellicle (cellular 'skin'). They move in a helical rotation of the cell. Some have green chloroplasts and photosynthesize to eat.* Others engulf their food or absorb it from their surroundings.
• The Kinetoplastea have a prominent kinetoplast which helps energize the main flagellum. Most are parasites. In humans the Trypanosomes cause sleeping sickness and Chagas disease; the Leishmania cause leishmaniasis. (Insects serve as secondary hosts.)
• The Diplonemea have short flagella with no support rods. They move by a 'writhing' or squirming motion and live mostly in marine sediments.

The relationship of the Euglenozoa to the Heterolobosea and the Jakobida has been genetically established. Speculation on classification within the Euglenozoa continues.

*The Euglenida chloroplasts presumably originated from some ingested green alga. They are pigmented with chlorophylls a and b, giving them a bright green color, and bound by three membranes. These Euglenida use a storage carbohydrate unique to the group. Most also have an 'eyespot' - a small splotch of red pigment near the base of the leading flagellum. The pigment shades a batch of light sensitive crystals which act together as a directional 'eye'. The cytostome mouth is vestigial, although nutrients may still be obtained by absorption.