Euglenozoa


The euglenozoa are a large group of flagellate Excavata. They include a variety of common free-living species, as well as a few important parasites, some of which infect humans. There are two main subgroups, the euglenids and kinetoplastids. Euglenozoa are unicellular, mostly around in size, although some euglenids get up to long.

Structure

Most euglenozoa have two flagella, which are inserted parallel to one another in an apical or subapical pocket. In some these are associated with a cytostome or mouth, used to ingest bacteria or other small organisms. This is supported by one of three sets of microtubules that arise from the flagellar bases; the other two support the dorsal and ventral surfaces of the cell.
Some other euglenozoa feed through absorption, and many euglenids possess chloroplasts, the only eukaryotes outside Diaphoretickes to do so without performing kleptoplasty, and so obtain energy through photosynthesis. These chloroplasts are surrounded by three membranes and contain chlorophylls A and B, along with other pigments, so are probably derived from a captured green alga. Reproduction occurs exclusively through cell division. During mitosis, the nuclear membrane remains intact, and the spindle microtubules form inside of it.
The group is characterized by the ultrastructure of the flagella. In addition to the normal supporting microtubules or axoneme, each contains a rod, which has a tubular structure in one flagellum and a latticed structure in the other. Based on this, two smaller groups have been included here: the diplonemids and Postgaardi.

Classification

The euglenozoa are generally accepted as monophyletic. They are related to Percolozoa; the two share mitochondria with disk-shaped cristae, which only occurs in a few other groups.
Both probably belong to a larger group of eukaryotes called the Excavata. This grouping, though, has been challenged.

Phylogeny

The phylogeny based on the work of Cavalier-Smith 2016.
Euglenozoa phylogeny

Taxonomy

Phylum Euglenozoa Cavalier-Smith 1981 emend. Simpson 1997