Zoology 10th Edition by Stephen Miller,John Harley

Exercise 6

Molluscs are lophotrochozoans with distant ties to the Annelida and other phyla. They originated more than 500 million years ago. Members of the classes Caudofoveata and Solenogastres probably most closely resemble ancestral molluscs. Molluscs underwent rapid adaptive radiation during the Cambrian period.
What features of members of the class Polyplacophora suggest that they were derived after solenogasters and caudofoveates, but before all other molluscs?
FIGURE 11.24 Molluscan Phylogeny. Cladogram showing possible evolutionary relationships among the molluscs.