Th e gastrointestinal tract of lungfi shes contains a spiral valve, as do the intestines of lampreys, elasmobranchs, sturgeons and coelacanths. A spiral valve intestine is generally considered an original way of achieving increased surface area for absorption of nutrients. Th e spiral valves are most commonly confi ned to the intestine distal to the duodenum or at least distal to the pyloris of the stomach. However, in Neoceratodus, the coiling commences immediately beyond the oesophagus at the point (glottis) where the pneumatic duct exits. Th is chapter discusses the spiral valve intestine of Neoceratodus and compares it to that of the lepidosirenid lungfi shes. Th e intimate relationship between the spiral valve intestine and the two lobes of spleen and the pancreas is described. Th e chapter fi nishes with descriptions of the liver and bile salts, the haemopoietic nature of the spleen and the presence of lymphoid tissues in the lungfi sh gut. It also includes a note on the only digestive system-related trematode parasite to have been described in lungfi sh. Keywords: Neoceratodus, spiral valve intestine, pyloric fold, lymphoid tissue, spleen and pancreas

Th e digestive system of lungfi shes is peculiar among bony fi shes in that increased surface area for absorption of nutrients is provided by a spiral valve. Th ere are several descriptions of lungfi sh spiral valve intestines in the older literature but there is only one relatively recent detailed anatomical description (Rafn and Wingstrand 1981) of Neoceratodus forsteri, which is arguably the most aberrant

of the three living lungfi sh genera. In this chapter we will discuss the study of Rafn and Wingstrand (1981), including where appropriate, our own more recent observations on the intestine of Neoceratodus (Hassanpour and Joss 2009). In our recent study more detailed anatomical and histological features of this structure are depicted. Th ere has been almost nothing published on the physiology of lungfi sh digestion. Th e endocrine cells of lungfi sh intestine and pancreas are discussed in the chapter on the Endocrine System (this volume) and the unusual dentition of lungfi sh in the chapter on Teeth (this volume). In this chapter we will include lymphoid tissue associated with the lungfi sh intestine and spleen, and haemopoiesis associated with the spleen. We will also mention lungfi sh gutassociated parasites.