A shift to an ion regulatory role by gills of a semi-terrestrial crab,
Ocypode stimpsoni. Zoological Studies 51(5): 606-618. Ocypode stimpsoni is a highly terrestrial species of
the Ocypodidae that faces challenges of both gas exchange and hypotonic stress when on land. The aim of
this study was to investigate the impacts of terrestrial modifications on the ion regulatory mechanism of the
gills in this semi-terrestrial crab. Our results showed that the lungs were the air-breathing organ and may take
the place of anterior gills for gas exchange. Epithelial cells in the anterior gills changed from a thin epithelium
for gas exchange to an intermediate type epithelium for ion regulation. We also found significantly higher
Na+, K+-ATPase activity in the anterior gills when crabs were transferred to 3‰ and 5‰ diluted seawater. The
ion regulatory proteins in both the anterior and posterior gills showed similar localization, an indication of the
involvement of the anterior gills in ion regulation. Cell thicknesses and Na+, K+-ATPase activity suggest that the
anterior gills can assist with ion regulation in acclimation to dilute seawater. We concluded that the presence of
the lungs caused the gills to be modified for ion regulation.
