Which one of the following is a character of all the members of Platyhelminthes, without any exception?

In all Platyhelminths flame cells are present for osmoregulation and excretion. Among platyhelminths, hooks and suckers are absent in free living forms (Planarians). Among Platyhelminths, gut is absent in Taenia solium. Lasso cells are present in ctenophores (e.g., Pleurobrachia).