Seagrass canopies harbor many different mollusc species, but information about the interaction of these seagrass residents with their host plants remains scarce. Most gastropods inhabiting seagrass meadows are believed to feed on epiphytes rather than directly on living seagrass tissues. In laboratory experiments, we demonstrate that the gastropod Smaragdia viridis (Linnaeus, 1758) feeds preferentially on three seagrass species that are common in the Caribbean and Bermuda, including Thalassia testudinum, Halodule wrightii, and Syringodium filiforme. The percentage of lysed over intact seagrass cells egested was significantly higher in gastropods fed either T. testudinum or H. wrightii (80.3 ± 4.7% and 84.6 ± 11.4%, mean ± SD) but not for S. filiforme (59.7 ± 15.9%). Diet versatility for both pioneer (H. wrightii and S. filiforme) and climax (T. testudinum) Caribbean seagrass species allows S. viridis to adapt to small-scale disturbances that are common in these habitats, but a diet specializing in seagrass may make this animal vulnerable to large-scale seagrass declines occurring worldwide.