So far, I have only found Amphileptus carchesii once on a colony of the peritrich ciliate Carchesium polypinum. Amphileptus carchesii parasitizes colonies of Carchesium polypinum and other peritrich ciliates (e.g., Vorticella sp.). In this case, the infested colony was on a submerged slide on which growth had developed within 9 days.

There are still very few records of this rare species. As far as I know, detailed descriptions are only available from Schneider (1988) and Foissner et al. (1992). The specimens are almost never found free-swimming, but mostly on colonies of the peritrich ciliate Carchesium polypinum. On these colonies, Amphileptus carchesii lives and feeds on the zooids. Each specimen of Amphileptus carchesii ingests about 40 zooids per day (Foissner et al., 1992). In doing so, Amphileptus carchesii always attacks the oral apparatus of the zooids with its extrusomes. The zooids, which are then paralyzed, are swallowed whole. Well-nourished specimens eventually form cysts, which can be found attached to the stalks of the colony.

Amphileptus carchesii is extremely well adapted to a parasitic life on colony-forming, peritrichous ciliates. In order to never lose contact with the host colony, Amphileptus carchesii forms a thread at its posterior end, with which the individuals attach themselves to the stalks of the colony (s. fig. 3). The thread is lengthened with every movement, so that the stalks of infested colonies are often wrapped in many threads. The thread is formed in a groove at the posterior end on the right side. The groove is called the fossa. Exactly how the thread is formed is not clear. Under light microscopy, it can be seen that the fossa is lined with parallel rows of bristle-like short cilia. Between these rows of cilia, just beneath the pellicle, there are rows of densely packed vesicles (s. figs. 7 a-b and 8). Possibly, the contents of these vesicles provide the components to form the thread.

Amphileptus carchesii can easily be confused with the similar species Amphileptus claparedii, which also parasitizes colonies of peritrichous ciliates, especially Carchesium polypinum. However, Amphileptus claparedii does not possess a fossa and only has two macronuclear nodules. Furthermore Amphileptus claparadii lacks extrusomes.