Term now used instead of herpetomonad for the stage of development of certain insect-parasitizing and plant-parasitizing flagellates to avoid confusion between the stage and the genus Herpetomonas. In this stage the flagellum arises from the kinetoplast located behind the nucleus and emerges from the anterior end of the organism; an undulating membrane is absent. [opistho- + G. mastix, whip]