Studies on the ultrastructure of candidate "cysts" in Leptomonas species of siphonaptera

Ultrastructural studies on Leptomonas ctenocephali of Ctenocephalides canis and Leptomonas species of Orchopeas h. howardi and Palaeopsylla m. minor have demonstrated the presence of characteristic round and oval parasites with a regularly indented plasma membrane. Such forms were found only as unattached parasites in the lumen of the pylorus, hindgut, and rectum amongst parasites which showed a normal kinetoplastid plasmalemma. The plasmalemma indentations are regular in their distribution around the periphery of the parasite, being separated usually by a fixed number of subpellicular microtubules in each "cyst-like form", some subpellicular microtubules are displaced from the periphery at the point where the plasmalemma is indented furthest into the cytoplasm. It is suggested that these forms meet the criteria necessary to be characterised as "cyst-like forms" despite the apparent absence of a true cyst wall.