Book excerpt: Part 3 of this book series puts the invertebrates of the North Sea, from molluscs to diverse cnidarians, in the context of the changing living conditions in this small part of the one big ocean. The book presents a balance between long established species and immigrants from the subtropics. Aspects of fishing, ecology and aquarium keeping were also included in this work. In addition, the preservation of cephalopods was also addressed. It would be very welcome, if in the future more people would concern themselves with the care and preservation of the wondrous and multifarious inhabitants of the North Sea. For unfortunately, many of the species shown here seem to be largely unknown to a wider public, which is why they hardly seem to have a real lobby in practice. So, we should better get to know our endemic species, before they become extinct.