 Through a hyperosmotic active transport process, the ammonite emptied water out of these shell chambers.This enabled it to control the buoyancy of the shell and thereby rise or descend in the water column.A primary difference between ammonites and nautiloids is the siphuncle of ammonites (excepting Clymeniina) runs along the ventral periphery of the septa and camerae (i.e., the inner surface of the outer axis of the shell), while the siphuncle of nautiloids runs more or less through the center of the septa and camerae.