MantlePearl– Countercurrent exchange– The molluscan coelom is very small (and has nolocomotory role), being restricted largely to the areasurrounding the heart and gonads– Blood sinuses comprising a hemocoel, which serves as ahydrostatic skeleton in the locomotion of some molluscs– Radula: chitin and protein– All fossilsClass Rostroconchia喙殼綱– Only one class of molluscs, the Aplacophora, hasapparently left no fossil record