Polychaeta is one of the class of annelid worms. There are three classes in Annelids namely, Oligochaeta, Polychaeta and Hirudinea. These organisms are generally marine. They include the fan worms, paddle worms and sand worms. Merostomata, Chilopoda, Crustacea are the classes of arthropods.
Thus, the correct answer is option B.