Sea mussels form dense aggregations on temperate rocky shores; however, in the absence of such firm substrates, biogenic surface such as the calcified integument of crustaceans may become settlement sites for their larvae. In this paper we present the first report on the association between the California mussel Mytilus californianus Conrad, 1837 and the Pacific sand crab Emerita analoga (Stimpson, 1857), collected from a sandy beach in Monterey Bay, California, U.S.A. We examined 63 crabs, and three had epibiotic mussels attached on their lateroventral surfaces. The organisms were measured and photographed. Such low incidence rate is tied to the collection site, as sandy beaches are considered atypical habitats for this bivalve species. The occurrence of epibiotic M. californianus suggests a random and non-obligatory relationship with E. analoga.