Prey choice is the non-random foraging and consumption of prey species by their predators, and is therefore the basis for studies of topics as diverse as quantifying food webs, predator–prey relationships, and optimal-foraging models. Malaclemys terrapin (Diamond-back Terrapin) is a diet generalist with a large geographic distribution: the US Atlantic and Gulf coasts from Massachusetts to Texas. Individual terrapins have relatively small home ranges and feed primarily on local mollusc species. In feeding trials with 1 prey species and 2 prey species, wild-caught terrapins from New York readily consumed Mya arenaria (Soft-shelled Clam) and Geukensia demissa (Atlantic Ribbed Mussel), preferring them over a wide range of other prey species commonly eaten by terrapins at other sites. Our correlation test indicated that Ulva latuca (Sea Lettuce), common in the diets of this population, is ingested incidentally when terrapins forage for Soft-shelled Clams. The impact of consumption of algae by this primarily molluscivorous turtle is unexplored, but could have important impacts on their energy balance and contaminant intake.