**4. Conclusions**

The potential use of the jellyfish *Rhizostoma luteum* as biomass, evaluating their nutraceutical value and antioxidant properties, has never been evaluated until the present study. The results presented here sugges<sup>t</sup> this jellyfish to be an excellent candidate for the potentially sustainable production of nutraceutical, cosmeceutical and biomedical natural products due to the highest antioxidant activity ever measured in a jellyfish, but also for their high content in PUFAs, including the essential fatty acid linoleic. Because the present work has been performed with young medusae, further work should be carried out with adult specimens. The large natural biomass of *Rhizostoma luteum* in nature, the wide geographical spread, and the fact that already its life cycle has been completed in captivity establishes a promising positive potential of this giant jellyfish species and the isolation of bioactive compounds for future use in marine biotechnology.

**Author Contributions:** Conceptualization, Investigation, Resources, Funding Acquisition and Writing-Original Draft Preparation, L.P. and M.J.O.; Methodology and Validation, M.J.O.; Formal Analysis, A.E.-N., R.L.V. and M.J.O.; Data Curation, L.P., M.J.O. and A.E.-N.; Writing-Review and Editing, all authors; Supervision, L.P. and M.J.O.; Project Administration, L.P.

**Funding:** This research was funded by the Spanish Ministerio de Ciencia, Innovación y Universidades under gran<sup>t</sup> number CTM2016-75487-R for the project MED2CA and the CSIC under gran<sup>t</sup> number 2017301072. The research stay of R.L.V. was funded by Erasmus + Program.

**Acknowledgments:** We thank A. Moreno and P. Gento for their technical assistance in the laboratory to rear the jellyfish.

**Conflicts of Interest:** The authors declare no conflict of interest.
