**Preface to "Jellyfish and Polyps"**

Climate change and other concurrent anthropogenic causes are influencing the frequency and abundance of jellyfish blooms, with large impacts on the structure and functioning of marine plankton ecosystems, as well as on human activities in coastal zones. In parallel, sea anemones, corals and less familiar forms of benthic polypoid cnidarians constitute a major group of suspension feeders governing the energy transfer from water column to seafloor organisms.

Their outstanding ecological importance in worldwide marine ecosystems calls for increased global monitoring of cnidarian ecology and life cycles. At the same time, many cnidarians are now regarded as a potential sustainable resource, calling for new investigations on their chemical and biochemical composition, the physical–chemical features and supramolecular organization of their protein components, the screening and identification of bioactive molecules, the associated microbiota and their sustainable biotechnological exploitation in different fields of applied research.

The apparent vulnerability of their soft bodies, coupled to their limited swimming ability and wide biodiversity with about 13,400 living described species, make cnidarians the top candidate for the development of biochemical strategies for survival (feeding, defense) and reproduction, including symbiosis or other relationships with microbes and other organisms. Venomous compounds occurring in extracts of cnidarians are viewed with particular interest for both aims of the mitigation of their adverse effects and their possible beneficial use for humans. Furthermore, in the pharmacopeia of traditional medicine of Eastern Countries, jellyfish are regarded as a treatment for disorders and diseases and represent a valuable foodstuff with health benefits, suggesting the occurrence of bioactive compounds that could be useful as nutraceuticals. Despite the increasing attention concerning jellyfish blooms, scientific knowledge of their biology, biochemical composition and potential in drug discovery, supporting their possible utilization and exploitation, is still limited.

This Special Issue collects novel research papers and original reviews focusing on bioprospecting marine cnidarians and on the exploitation of their biomasses and derived compounds for biotechnological and biomedical applications, as well as active ingredients for pharmaceutical, nutraceutical, cosmetic and cosmeceutical uses.

### **Antonella Leone, Gian Luigi Mariottini, Stefano Piraino**

*Editors*
