Euglenozoa
Euglenoidea
Kinetoplastea
Diplonemea
Postgaardea
</table>
The
Euglenozoa are a large group of
flagellate protozoa, dominated by the
euglenids and
kinetoplastids. They include various common free-living forms as well as a few important parasites, some of which are parasitic in humans. Most are small, around
15-40 µm in size, although many euglenids get up to 500 µm long. They were first defined by
Cavalier-Smith in 1981, often ranked as a phylum.
Most Euglenozoa have two
flagella, usually one leading and one trailing, which insert parallel to each other in an apical or subapical pocket. In most forms there is an associated cytostome (mouth) supported by one of three
microtubule groups that arise from the flagellar bases. These are characteristic of the group; the other two support the
dorsal and
ventral surfaces of the cell, and in the euglenids support proteinaceous strips that form a pellicle. A number of other ultrastructural peculiarities also distinguish the group, most notably the presence of a paraxial rod in each flagellum, which respectively have tubular and latticed structures.
Most Euglenozoa feed by ingesting smaller organisms, typically
bacteria, or by absorption. A number of euglenids, however, possess
chloroplasts and so produce energy through photosynthesis. These have generally lost the cytostome and often have other adaptations to an autotrophic life, such as light-sensitive eyespots. The chloroplasts are contained in three membranes and are pigmented similarly to the
plants, suggesting they were retained from some captured
green alga.
All Euglenozoa have
mitochondria with discoid cristae, which in the kinetoplastids characteristically have a DNA-containing granule or
kinetoplast associated with the flagellar bases. No examples of
sexual reproduction in the group have been found. Reproduction is exclusively through cell division, characteristically with closed
mitosis involving an internal spindle. The monophyly of the Euglenozoa is generally accepted, and they are believed to be related to the
Heterolobosea and other
excavate flagellates.
