I am looking for comparative data on the amount, size and shape of "hard parts" (hooks, etc.) of parasitic helminths, particularly parasitic flatworms (Neodermata: monogeneans, trematodes and cestodes) and Acanthocephala.
Keys to the Cestode Parasite of Vertebrates (http://www.cabi.org/bookshop/book/9780851988795) is the most recent concept on the systematics of main orders of tapeworms. You will find enough information and illustrations of hooks.
Similarly, there are three volumes of keys to trematode parasites, a fundamental series on the systematics and identification of the class Trematoda.