The oceans are a vast, albeit unexplored, source of novel substances with high potential biotechnological value. Although one of the most diverse and abundant group of organisms in the seas, occupying almost every known marine habitat, from the intertidal to deep-sea vents, the Polychaeta are scarcely known with respect to their physiology and biochemistry. As a consequence, the knowledge on these organisms’ biotechnological potential is essentially absent. Previous research disclosed the endogenous production of a potent peptidic toxin by specialized skin cells of the common polychaete Eulalia viridis (Errantia: Phyllodocidae), isolated from the mucous, and a complex pattern of endogenous pigments holding resemblance to porphyrin derivatives (to which the species owes its bright green colour). All these novel substances, i.e., the toxin (here forth referred to as mucotoxin) and pigments, although not yet fully characterized, yielded highly promising results in preliminary toxicity testing with Vibrio fischeri (through the Microtox assay) and human cancer cell lines. Whereas the mode-of-action of the worm’s mucotoxin remains unknown, porphyrin-like pigments have been gaining particular attention as photosensitizers in photodynamic therapy (PDT). This recent therapeutical approach has been rising as an alternative for the treatment of a multiplicity of skin disorders, with emphasis on aggressive malignancies such as melanomas, which is typically resistant to traditional chemical and radiation therapies. Nonetheless, the current limitations on variety and source of adequate photosensitizers are an acknowledged handicap for the prospects of PDT as an effective alternative treatment to the traditional therapies, which are costly and aggressive. As such the GreenTech project is designed to become a novel approach within the field of Marine Biotechnology by steering a multidisciplinary research team towards the application of novel marine biosubstances in biomedical research. In brief, the project holds the following main objectives: i) to chemically characterize the mucotoxin (and potential isoforms) and main pigments; ii) to assess the main effects and targets of the substances in vitro through a battery of tests with human cell lines (cancer and normal), and iii) to test the substances in vivo taking the zebrafish as model. In the latter case, whereas the mucotoxins’ effects and mechanisms will be screened systemically in wild-type animals (to detect most possible outcomes, from teratogenesis to neurotoxicity), the pigments’ value as photosensitizers for PDT will the inferred from a battery of tests using the melanoma phenotype zebrafish, taking advantage of transgenic lines to express human oncogenes involved in the formation of this type of neoplasic disease. Not only will tumour regression be monitored after localized photosensitization in fish injected with the pigments, but also potential side effects in surrounding normal tissue and systemic alterations as well (e.g., inflammation-related).