Euglenozoa

The Euglenozoa comprise a few major groups of flagellate protozoa whose relationships to one another have only recently been recognized: the kinetoplastids, the euglenids, the diplonemids and possibly a few other forms. They include various common free-living forms, mostly bacterivores, as well as a few important parasites. Most are around 15-40 µm long, although a many euglenids get up to 500 µm.

Most euglenozoa have two flagella, usually one leading and one trailing, that insert parallel to each other in an anterior pocket. In most forms there is a cytostome (mouth) associated therewith, supported by one of three characteristic microtubule groups arising from the flagellar bases; the other two support the dorsal and ventral surfaces. There are a number of other ultrastructural peculiarities, for instance, paraxial rods inside the flagella.

No example of sexual reproduction has ever been found within the group. They reproduce exclusively through cell division, with closed mitosis and internal spindles. All euglenozoa have mitochondria with discoid cristae, and are possibly distant relatives of other such groups - eg Heterolobosea, Stephanopogon.

A number of euglenids possess chloroplasts. These are typically contained in three cell membranes, suggesting they were taken secondarily from some captured alga. The pigmentation is mostly similar to that of the Plantae. Photosynthetic euglenids have generally lost the cytostome and often have other adaptations to an autotrophic life - most interesting of which is a light-sensitive eyespot. A few have secondarily lost the chloroplasts and feed by absorption.