Among invertebrates cephalopods have evolved a high degree of behavioral and physiological complexity that is comparable to that found in vertebrates. This high-performance lifestyle, including well-developed sensory and locomotory abilities, is directly associated with high energetic costs that require efficient metabolic and regulatory pathways to maintain body homeostasis. Amino acid catabolism is the major energy source in cephalopods with ammonia being the major metabolic end product. Furthermore strong fluctuations in extracellular pH during exercise have led to the presence of ion-regulatory epithelia that highly express a conserved set of ion transporters to mediate extracellular acid–base homeostasis and excretion of nitrogenous waste products.
Hu M. & Tseng Y.-C., 2017. Acid–base regulation and ammonia excretion in cephalopods: an ontogenetic overview. In: Weihrauch D. & O’Donnell M. (Eds.), Acid-base balance and nitrogen excretion in invertebrates: mechanisms and strategies in various invertebrate groups with considerations of challenges caused by ocean acidification, pp. 275-298. Springer International Publishing. Book chapter (subscription required).