It may indeed surprise young readers ""to be told that the sponge you use for your bath. . . can actually be a skeleton."" That's how Jacobson and Pang begin, and not until toward the end do they even refer to that unnamed, unnatural ""other kind"" (the low-priced spread?). Given such partiality and their declaration that sponges differ so much from all other animals, both proto-and metazoa, that ""they have a whole subkingdom (parazoa) to themselves,"" you might expect something less routine than this introduction which proceeds predictably from sponge classes (the emphasis is on terminology) to life functions (few) to uses to tips on keeping a sponge collection. Not absorbing, then, but it covers the subject.