Essential component of the mitotic checkpoint, which prevents cells from prematurely exiting mitosis. Required for chromosome segregation, the assembly of the dynein-dynactin and mdf-1-mdf-2 complexes onto kinetochores and spindle pole separation. Its function related to the spindle assembly machinery and kinetochore-microtubule attachments likely depends on its association in the mitotic RZZ complex. The RZZ complex recruits the spindly-like protein spdl-1 to kinetochores. To prevent irregular chromosome segregation, the complex also inhibits the attachment of the kinetochore-associated NDC80 complex to microtubules. The recruitment of spdl-1 to kinetochores relieves this inhibition. Required for embryonic development. Component of the RZZ complex composed of rod-1, czw-1 and zwl-1. Interacts with the spindly-like protein spdl-1. Interacts with NDC80 complex component ndc-80. Localizes to the kinetochore during nuclear envelope breakdown and remains there until the metaphase-anaphase transition. Localizes to kinetochores, spindle-associated rod-shaped structures and near the cell cortex in a knl-1-dependent manner in anaphase. Belongs to the ZWILCH family.