The Nautilus Siphuncle as an Ion Pump

Abstract

The siphuncle, which is believed to empty the newly formed chambers of the shell by a process involving the active transport of NaCl, has the metabolic, enzymatic, and morphological features of a transporting epithelium. It is capable of removing monovalent ions from solutions containing only Na+ and no Cl- or divalent ions, or only Cl- and no Na+ or divalent ions, indicating no obligatory coupling. The Na+ and Cl- are removed from native cameral fluid at approximately the same ratio. The levels of K + and the divalent ions are also lowered, but at slightly different rates. Neither H+ nor NH1 accumulate in cameral fluid to an appreciable extent.