The marine environment is proving to be a very rich source of unique compounds with significant activities against cancer of several types. Finding the sources of these new chemical entities has made it necessary for marine and medical scientists to find enterprising ways to collaborate in order to sample the great variety of intertidal, shallow and deep-water sea life. Recently these efforts resulted in a first generation of drugs from the sea undergoing clinical trials. These include PharmaMar compounds: Yondelis, Aplidin, kahalalide F, ES285 and Zalypsis. Two of these compounds, kahalalide F and ES285, have been isolated from the Indopacific mollusc Elysia rufescens and the North Atlantic mollusc Spisula polynyma, respectively.