Nitrogen Excretion in Ascidiacea

Ascidians have hitherto been regarded as eliminating their nitrogen in an insoluble form and storing the products either in special vesicles or in blood cells termed nephrocytes. Three species of ascidian have been studied: Ciona intestinalis, Ascidiella aspersa and Molgula manhattensis. Evidence is brought forward to show that these ascidians excrete soluble nitrogen chiefly in the form of ammonia. The quantities of soluble non-protein nitrogen excreted are slightly higher than is found in the filter-feeding molluscs; this is probably due in part to an increased metabolic rate subsequent to transport and handling. Ammonia may form as much as 95% of the total non-protein nitrogen excreted. The methods employed are subject to an error up to 10%.