This is a review of recent studies on relationships between reproductive ecology, ontogeny of osmoregulation, and larval salinity tolerance in congeneric sesarmid crabs from Jamaica: Armases ricordi (H. Milne Edwards), A. roberti (H. Milne Edwards) and A. miersii (Rathbun).In the semiterrestrial coastal species A. ricordi, the zoeal stages tolerate only moderately reduced salinities (17-25), in which they are capable of hyper-osmoregulation. The megalopa is the first ontogenetic stage of this species, which exhibits significant hyper-osmoregulation and tolerance of lower salinities (&#8805;5), as well as a moderately developed function of hypo-regulation at high salt concentrations (32-44).In the riverine species A. roberti, the first zoeal stage shows, already at hatching, a strong capability of hyper-osmoregulation, surviving for up to two days in freshwater (<0.2). Interestingly, this early expressed physiological function becomes significantly weaker in the subsequent zoeal stages, where survival and hyper-osmoregulation were observed only at salinities &#8805;10. The capability of hyper-regulation in strongly dilute media re-appears only in the megalopa stage, which tolerates even an extended exposure to freshwater.Similar to A. roberti, the semiterrestrial coastal species A. miersii shows already at hatching a strongly developed function of hyper-osmoregulation in salinites down to 1, corresponding with tolerance of very low salinities. In contrast to A. roberti, however, these capabilities increase gradually throughout larval and juvenile development. In all three species compared here, the pattern of hyper-hypo-osmoregulation appears, for the first time in ontogeny, in the megalopa stage, and it increases after metamorphosis and throughout juvenile development.These species- and stage-specific patterns of osmoregulation and larval salinity tolerance are compared with contrasting life styles, reproductive behaviours, and life-history strategies. In A. ricordi, the larvae are directly released into coastal marine waters, where salinities are high, and thus, no strong hyper-osmoregulation is needed throughout the zoeal phase. The megalopa stage of this species, by contrast, may invade brackish mangrove habitats, where osmoregulatory capabilities are required. Strong hyper-osmoregulation occurring in both the initial and final larval stages (but not in the intermediate zoeal stages) of A. roberti corresponds to the tentative pattern of ontogenetic migration in this species: hatching in freshwater, larval downstream transport, later zoeal development in brackish estuarine or coastal marine waters, and final re-immigration of megalopae and juvenile crabs into limnic habitats, where the conspecific adults live. In A. miersii, the ontogenetic pattern corresponds with an unusual reproductive biology: it breeds in supratidal (i.e. land-locked) rock pools, where variations in salinity are high and unpredictable.Matching patterns in the ontogeny of osmoregulation and life-history strategies indicate a crucial adaptive role of osmoregulation for invasions of (by origin marine) crabs into brackish, limnic and terrestrial environments.