In sex-changing animals with internal fertilization, gregarious behavior may increase mating opportunities and the frequency of multiple paternity, thus increasing maternal reproductive success. Crepidula convexa is a direct-developing protandrous gastropod characterized by only modest gregarious behavior compared with previously studied members of the genus: females are frequently found isolated. Using 6 microsatellite markers, we analyzed paternity profiles in 10 broods (25 embryos per mother). The number of assigned fathers varied among families from 1 to 4 fathers per brood. Interestingly, polyandry was not detected in solitary females but only in females grouped with conspecific individuals. Overall, we found an average of 1.8 fathers per brood, but this increased to 2.6 fathers per brood when considering only the nonisolated females. Among 18 unambiguously identified fathers, only 5 were collected in our samples, suggesting substantial male mobility. Comparison with previous paternity analyses in Crepidula fornicata and Crepidula coquimbensis revealed that polyandry appears as a common trait of these sex-changing gastropods despite their different grouping behaviors and life histories. As expected, the level of polyandry was nevertheless lower in the modestly gregarious C. convexa.