Mollusca have one heart while Annelids have five heartsMollusca can have open circulatory system but Nematoda and Platyhelminthes have closed circulatory systemMollusks are marine creatures while Nematoda and Platyhelminthes are land creaturesMollusks have a more complex system then any other phylaMollusks have shells, either externally or internally, but phylum such as Cnidarians, Annelids, Nematoda and Platyhelminthes do not