Ciliates differ from all other protozoans in: using pseudopodia for capturing prey; using flagella for locomotion; having two types of nuclei; having a contractile vacuole for removing excess water.

The correct option is C: having two types of nuclei. The ciliates are a group of protozoans characterized by the presence of hair-like organelles called cilia. Cilia are used for locomotion and food gathering. Another characteristic of ciliates that differ from all other protozoans is having two types of nuclei, namely somatic macronucleus and germline micronucleus. Thus, the correct answer is option C.