As of Sept 30th, a paperback edition will be available at a very reduced price. Pre-orders can be made.
See:
https://www.routledge.com/Biology-and-Evolution-of-the-Mollusca-Volume-1/Ponder-Lindberg-Ponder/p/book/9781032176604
https://www.routledge.com/Biology-and-Evolution-of-the-Mollusca-Volume-2/Ponder-Lindberg-Ponder/p/book/9781032173542