Originating from the sea, some decapod groups have invaded brackish and freshwater habitats. Such evolutionary transitions require major physiological adaptations, in particular hyper-osmoregulation at reduced salinities. In most non-marine species, however, this capability occurs only in the benthic juvenile-adult phase, while the pelagic larval stages are osmoconformers or weak hyper-regulators which develop in coastal marine waters. This implies ontogenetic changes in physiological features including osmoregulation. Integrating information from ontogenetic patterns of larval dispersal, salinity tolerance, and osmoregulatory functions and structures, we propose an ecophysiological classification from fully marine to fully limnic species. (1) Fully marine or coastal species (e.g. Hyas, Homarus spp.). (2) Coastal and estuarine species, with hatching at reduced salinities, larval export towards the sea (by passive drift and/or female migrations), and postmetamorphic return to adult habitats (e.g. Carcinus maenas, Crangon crangon, Callinectes sapidus). (3) Coastal species with larval retention in habitats with low or variable salinity (e.g. mangrove swamps, rock pools, rainfall puddles; Sesarma curacaoense, Armases miersii, Uca subcylindrica); in species living in semiterrestrial mangrove or salt marsh habitats (e.g. Sesarma curacaoense, Chasmagnathus granulata), the stage of settlement (the megalopa) may also develop the function of hypo-osmoregulation at enhanced salinities. (4) Species with hatching in saline water after female migration from freshwater (Macrobrachium petersi, Eriocheir sinensis). (5) Species inhabiting freshwater or adjacent brackish habitats, with larval retention (Palaemonetes argentinus). (6) Fully limnic species with abbreviated or omitted larval phase; larvae (when present) or juveniles must be strong hyper-regulators (some species of Palaemonetes, Astacus spp.).