genus of parasitic protozoa (suborder Trypanosomatina, order Kinetoplastida) found in the digestive tract of arthropods and other invertebrates; adult form is similar to the leptomonads, but the flagellum arises from the kinetoplast just in front of the nucleus, and is attached to the body by an undulating membrane; during their life cycle the organisms pass through choanomastigote (promastigote) and amastigote stages.