The article provides a review of research on evolution, ecology and physiology of aging and longevity, and focuses on results gained from the studies of a facultatively sexual crustacean, Daphnia. Despite its clonality and indeterminate growth, evidence for its senescence has been collected. Differences in the dynamics of age- specific parameters were seen between both environmentally developed phenotypes within a genotype and between genotypes, including between sister species. The lifespan of the animals varies depending on the habitat of origin and predation pressure experienced therein, and on environmental conditions - showing a hormetic response, or revealing trade-offs in the life history. Extreme differences in lifespan can be found in closely related lineages and within a single habitat, providing opportunities to study the underlying mechanism. This all makes Daphnia a so-far underscored, but already emerging model in the study of ecology and evolution of aging, and its molecular mechanisms.