Recent Nautilus pompilius from the Fiji Islands and N. macromaphalus from New Caledonia show decreasing cameral liquid volumes relative to total phragmocone volume during ontogeny. A maximal value of 32% of the phragmocone filled with cameral liquid was measured from a 190 g N. pompilius. No specimens of over 500 g total weight of either species exceeded 12%. These figures are in contrast to values derived for seven ammonoid species by Heptonstall (1970), who found values ranging between 19 and 52%.
The relationship between cameral liquid volume and salinity within single chambers engaged in the emptying process are examined in N. pompilius and N. macromphalus. Both species start with newly formed chambers filled with cameral liquid isotonic to seawater. Ionic removal by the siphuncular epithelium rapidly reduces the cameral liquid osmolarity, producing osmotic movement of the cameral liquid into the blood spaces of the siphuncle. In both species the lowest cameral liquid salinities occur when the chamber is slightly over half emptied. After this point, which coincides with decoupling of the cameral liquid from the siphuncle, cameral liquid volume continues to decrease, but cameral liquid salinity increases, indicating that the rate of ionic removal slows relative to liquid removal. In N. macromphalus decoupled cameral liquid salinity rises until it is nearly isotonic to seawater when the chamber is nearly emptied. In N. pompilius, however, the rate of ion removal in decoupled cameral liquid is not slowed as much as in N. macromphalus, since it rarely exceeds 40% seawater osmolarity even when the chamber is nearly emptied. The differences in emptying methods demonstrated in these two species are probably related to their different habitat depths: N. pompilius from Fiji is found in much deeper water and must employ more physiologic work to empty chambers at greater depth.