Acanthocephalans belonging to the species Acanthocephalus lucii were found in the colon of a lamb from ecological farms in the Czech Republic. The main determination features used for these acanthocephalans are the shape and size of the hooks as well as the number of hooks on the proboscis. Three immature specimens measured 5.0-13.2mm in length; the appearance of the acanthocephalan body (in the studied material) suggests that passage through this unusual host causes the cystacanths to slightly increase in length. In the case of the lambs examined, the infection may be acquired through the accidental ingestion of the intermediate host - waterlouse (Asellus aquaticus).