The ontogenetic development of the cephalobaenids Reighardia sternae and Raillietiella sp. was compared and considerable differences with regard to stage size, development terms, habitat preference, and feeding behavior were found. On the basis of these differences we present a new interpretation of the life cycle of R. sternae, considering this species as an obligatory one-host parasite that has shifted its intermediate host phase into the egg. Therefore, the hatching stage directly infects the respiratory system of the definitive host, which is unique among pentastomids.