Step 1: Evaluate each statement.
- (A): Ctenophora and Cnidaria are both part of the group Radiata and share a more recent common ancestor with each other than with Echinodermata. This is correct.
- (B): Porifera (sponges) are more closely related to Ctenophora than to Echinodermata. Porifera is a basal group, and Ctenophora and Echinodermata are both more derived, but this relationship is supported by molecular data. This is correct.
- (C): Arthropoda is more closely related to Tardigrada (water bears) than to Annelida. Molecular phylogenies support the idea that arthropods and tardigrades are more closely related, forming a group called Ecdysozoa. This is correct.
- (D): This is incorrect because Arthropoda is more closely related to Nematoda than to Mollusca, according to current phylogenetic studies. Arthropoda and Nematoda both belong to the group Ecdysozoa, while Mollusca is part of a different group, Lophotrochozoa.
Step 2: Conclusion.
Therefore, the incorrect statement is (D).