Ion regulation in invertebrates: Molecular and integrative aspects

The subject of ion regulation in invertebrates is discussed, using a variety of invertebrate model species and approaches that range from the whole-organism level to tissue, subcellular, and molecular levels to illustrate the future direction of the field. These organisms inhabit a variety of aquatic, freshwater, and terrestrial environments, showing specific adaptations to each environment. This overview discusses mechanisms of metal detoxification and the presence of Cl-ATPase in marine organisms to avoid excess intracellular Cl ^-; Ca²⁺ regulation and endocrine aspects of adaptations to transitional (semiterrestrial) environments; adaptations to Ca ²⁺-poor freshwater, particularly the reabsorption of Ca²⁺ through specific transporters found in the urine; and finally, ionoregulatory mechanisms for life on land, such as Ca²⁺ conservation during molting in isopods and the presence of K⁺ channels in insect Malpighian tubules. Convergent mechanisms for dealing with similar problems in dissimilar habitats are discussed, taking into consideration that invertebrates will continue to serve as model systems for the evolution of ionoregulation in different habitats.