Synonyms for Semiaquatic (same or very similar meaning)
WordNet sense 1 (having an aquatic early or larval form and a terrestrial adult form):
amphibioticWordNet sense 2 (operating or living on land and in water):
amphibiousWordNet sense 3 (partially aquatic; living or growing partly on land and partly in water):
subaquaticWordNet sense 4 (operating or living or growing in water):
aquaticFrom the ODE community, based on WordNetadd/edit