euryhalinity. Our present results suggest that the latter
feature was based upon an early ontogenetic appearance of osmoregulatory capabilities;
this should include, already from hatching, the occurrence of specialised ion-transporting
1 1 epidermal structures and enzymes, namely Na –K -ATPase (Charmantier, 1998). We
suggest that these traits represent important prerequisites for the evolutionary transition
from the marine intertidal through transitional habitats with a highly variable salinity
regime (e.g. estuarine mangrove swamps), and eventually, into limnic and terrestrial
habitats.