K+, and osmotic concentrations
The crabs were anesthetized and dissected, and ~300 µl (for H. tridens and C. dehaani ) or ~150 µl (for M. japonicus ) of hemolymph was collected from each crab. They were centrifuged at 2390 × g for 5 min at 4°C and the supernatant was collected to be used as the sample solution. Na+and K+ concentrations in 1:10 diluted and undiluted sample solutions, respectively, were measured using sodium (model C-122) and potassium ion meters (model C-131) (HORIBA, Kyoto, Japan), respectively. The osmotic concentrations were measured with a vapor pressure osmometer (Model 5600, Wescor, Logan, UT, USA).