The urchin Paracentrotus lividus has been characterized via previous capture and enhancement of lowabundance proteins with combinatorial peptide ligand libraries (CPLL, ProteoMiner). Whereas in the control only 26 unique gene products could be identified, 82 species could be detected after CPLL treatment. Due to the overwhelming presence of two major proteins—the toposome (a highly glycosylated, modified calcium-binding, iron-less transferrin) and the major yolk proteins, belonging to the class of cell adhesion proteins—which constituted about 70% of the proteome of this biological fluid and strongly interfered with the capture of the minority proteome, no additional proteins could be detected. Yet, at present, this constitutes the most thorough investigation of the proteome of this biological fluid.