This study examines the bryozoan fauna encrusting on the common Pacific half-slippersnail, Crepipatella lingulata. This suspension-feeding calyptraeid gastropod is common at shallow depths off the coast of California and is also common in the fossil record. The shell lengths of C. lingulata specimens dating back to the late Pliocene-early Pleistocene were examined, as well as the area of shells encrusted with bryozoans. Holocene shells were significantly larger than other shells, and modern (specimens collected in the present day) encrusted shells were significantly shorter than encrusted shells from the ancient past, but the latter could reflect collection bias. I also determined that modern shells are more fully covered with bryozoans than fossil shells. However, there was significant statistical interaction in the Holocene and modern data; thus, if more specimens were to be added that were relatively less prone to sampling biases from these time periods, the observed patterns could change. Finally, I identified bryozoan species encrusting on modern C. lingulata shells: 34 of the 41 specimens examined were found to be the species Rhynchozoon rostratum and, because one bryozoan species seems to dominate the encrustation, this implies a symbiotic association between C. lingulata and R. rostratum.