The correct option is
D Arthropoda
A) Platyhelminthes classes are: Turbellaria, Trematoda and Cestoda.
B) Annelida classes are: Polychaeta, Oligochaeta, Hirudinea, Archiannelida and Echiurida.
C) Mollusca classes are: Monoplacophora, Polyplacophora, Scaphopoda, Gastropoda, Pelecypoda and Cephalopoda.
D) Arthropoda classes are : Crustacea, Chilopoda, Diplopoda, Insecta, Archnida, Merostomata and Onychophora.
So the correct answer is 'Arthropoda'.