Observation of sutures in the oocyst wall of Eimeria tenella (Apicomplexa).

Eimeria tenella is the causative agent of caecal coccidiosis in chicken. Infection of chicken is initiated by ingestion of sporulated oocysts. The oocyst wall has two typical layers: a smooth outer layer formed by wallforming body I (WF I) and an inner layer originating from WF II. We observed that the inner layer is circumscribed by a hitherto undocumented linear suture and propose its role in the process of infection.