An animal whose body fluids are in osmotic balance with its environment. For many marine invertebrates the osmolarity and ionic concentrations of their body fluids are similar to those of the seawater in which they live. Such animals avoid the need to expend much energy on osmoregulation. However, they generally maintain cell volumes by altering the concentration of intracellular osmolytes. Compare osmoregulator.
Subjects: Biological Sciences.