Protists used to be classified in a single kingdom but scientists now realize protists are a very diverse group of eukaryotes. Currently their scientific classification is being debated but some taxonomists have placed them into seven major clades or branches. One of these is the euglenozoan clade noted for having a spiral or crystalline rod inside their flagella. Two examples of euglenozoans with these rods are:
1. kinetoplastids e.g. trypanosoma which causes African sleeping sickness and is spread by the tsetse fly.
2. euglenids e.g. euglena which is a commonly studied lab specimen
The flagella of kinetoplastids and euglenids have paraxial rods running next to each other. The paraxial rods of the euglenid ventral flagellum is lattice-like while the dorsal flagellum of the euglenid is whorled like a fingerprint.