like ectothermic and endothermic animals, do organisms differ in the way they maintain salt balance?

Yes, organisms differ in the way they maintain salt balance.

1. Animals can be either isosmotic to the surrounding (osmoconformers or control the internal environment independent of external environment (osmoregulators). 

2. Marine organisms are mostly osmoconfòrmers because their body fluids and external environment are isosmotic in nature while fresh water forms and terrestrial organisms are osmoregulators, 

3. Generally, most organisms can tolerate only a narrow range of salt concentrations. Such organism are known as stenohaline organisms. 

4. Organisms which are capable of handling a wide change in salinity are called euryhaline organisms.

e.g. Barnacles, clams etc.