 In general, they seem to maintain hypoionic concentrations of sodium, calcium, and chloride in contrast to the salt water.Sulfate and potassium exist in a hypoionic state, as well, with the exception of the excretory systems of cephalopods, where the urine is hyperionic.These ions are free to diffuse, and because they exist in hypoionic concentrations within the organism, they would be moving into the organism from the seawater.