Tube-building sabellariid polychaetes have major impacts on the geology and ecology of shorelines worldwide. Sandcastle worms, Phragmatopoma californica (Fewkes), live along the western coast of North America. Individual sabellariid worms build tubular shells by gluing together mineral particles with a multipart polyelectrolytic adhesive. Distinct sets of oppositely charged components are packaged and stored in concentrated granules in separate cell types. Homogeneous granules contain sulfated macromolecules as counter-polyanion to polycationic Pc2 and Pc5 proteins, which become major components of the fully cured glue. Heterogeneous granules contain polyphosphoproteins, Pc3A/B, paired with divalent cations and polycationic Pc1 and Pc4 proteins. Both types of granules contain catechol oxidase that catalyzes oxidative cross-linking of L-DOPA. Co-secretion of catechol oxidase guarantees rapid and spatially homogeneous curing with limited mixing of the preassembled adhesive packets. Catechol oxidase remains active long after the glue is fully cured, perhaps providing an active cue for conspecific larval settlement.