Predators may cause diversification of life-history traits between closely related prey species or between ecotypes within a species. Several possible instances of the diversification of life-history traits have been demonstrated between predator- and predator-free environments. Although divergence of life-history traits might result in speciation, evidence on this idea—the predator-driven speciation hypothesis—is insufficient both theoretically and experimentally, and there is also no information on the sympatric divergence patterns of life-history traits in prey species. Recent research proposed that two land snails, Karaftohelix editha and K. gainesi (Camaenidae, Stylommatophora), and their shared predators, malacophagous carabid ground beetles, distributed in northern Japan, can be an excellent model to explore the prey divergence via antipredator adaptations for some reasons. Although these two species were indistinguishable using several neutral DNA markers and shared their distribution area and habitats almost completely, there were vast inter-specific differences in various phenotypic traits, and almost all of them appeared to function as antipredator strategies. In this study, the ontogenetic growth patterns of K. editha and K. gainesi and their candidate ancestral species K. blakeana were investigated, which revealed several inter-specific differences in growth strategies. For instance, K. editha and K. blakeana, linearly increased their shell thickness throughout the entire growing stages, whereas K. gainesi drastically changed the growth rate of shell thickness along with each growing stage. All inter-specific differences discovered in this study may function efficiently as species-specific antipredator strategies for each species.