Leptomonads refer to the members of the genus Leptomonas. Certain literature thinks that the genus Leptomonas is perhaps the most primitive in the Trypanosomatidae (trypanosomatids).1 The trypanosomatids have different morphological forms in their life cycle. Some of the trypanosomatids appear as non-flagellated, non-ciliated round cell (referred to as amastigote); other forms are flagellated (referred to as promastigote). The genus Leptomonas of trypanosomatids have different morphological forms in their life cycle. For instance, they appear as flagellated. They have free flagella in contrast to other genus such as Trypanosoma with flagella connected to an undulating membrane. Leptomonads may eventually lose their free flagella and become a non-flaggelated round cell. The amastigote stage of the leptomonads is their infective form. A prospective host that ingests the cystic amastigote of leptomonad will harbor the parasite upon excystation.1
An example of leptomonad species is Leptomonas ctenocephali. This leptomonad parasite occurs in the hind gut of Ctenocephalides canis (dog flea). Its promastigote stage is usually found in the foregut of its host and when it reaches the hind gut it undergoes the amastigote stage.1
1 Cheng, T. (1986). General Parasitology. Burlington: Elsevier Science.