NITROGEN-EXCRETION IN THE ANTARCTIC LIMPET NACELLA-CONCINNA (STREBEL, 1908)

Excretion of ammonia, urea and primary amines (assayed as fluorescamine-positive substances, FPS) was measured in the Antarctic limpet Nacella concinna. The mean contributions to overall excretion rate were 89% ammonia, 8% urea and 3% FPS, although in some individuals urea formed almost 40% total excreted nitrogen and in others primary amines formed over 30%. Ammonia and urea excretion rates were not correlated, suggesting the ureagenesis has a specific physiological role and is not simply an alternative end-point to ammonia. In starved limpets urea excretion at first increased by at least x2, and then declined to low levels after 44 days. Ammonia excretion also increased, but only after 20 days, and then stayed high until at least day 44. These different patterns confirm the independent roles of ammonia and urea production in Nacella.