By Misty Lang with edits by Heidi Schutz

The digestive system begins at A. tridactylum's mouth, and the food bolus travels through the esophagus, stomach, small intestine, large intestine, and exits through the cloaca. In the mouth there are two parallel rows of monocuspid teeth (have only one point) on the upper jaw and the vomer bone, and one row on the mandible. The tongue is absent (Weigart and Churchill 1938). The esophagus, stomach, and small intestine are all lined with folds called rugae which are visible in Fig. 1. Dirt and fecal matter was found in our specimen’s large intestine / colon (see the left-most panel in figure 1). The cloaca is a multipurpose digestive, urinary, and reproductive structure.

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Figure 1. Amphiuma digestive tract removed from the body. Photo credit: M. Lang & N. Thach. Editing credit: N. Thach & M. Lang.

Comparative Anatomy:

The Amphiuma's digestive tract is very similar structurally to the cat. The cat's tract is a more specialized and complex with a duodenum and a fattier, more vascularized mesentery. Another difference is that feces are excreted through the anus in the cat which is completely separate form the urethra, where nitrogenous waste is excreted in the urine. The cloaca in Amphiuma on the other hand, has both reproductive and excretory functions as a single opening (Kardong, 2015) Overall, many of the same parts are present in each organism. See comparison below in Figure 2.

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Figure 2. Cat and Amphiuma digestive tract comparison. Photo credit: M. Lang & N. Thach.

When comparing A. tridactylum with the shark, the main similarity is that they both begin with food entering the mouth and going through the esophagus to the stomach. However, the shark’s intestine is shorter and notably different from the cat’s and Amphiuma’s. The shark is able to function with a shorter intestine because the valvular intestine contains a spiral valve that increases the surface area in the lumen. This maximizes the efficiency of digestion. Digestive waste products then travel to the colon and are excreted through a cloaca. Attached to the colon is the digitiform gland, a structure present in the shark but not in the cat or Amphiuma. This gland functions in salt excretion (Kardong, 2015).


Kardong, K.V. and Zalisko, E.J. (2015). Comparative vertebrate anatomy: A laboratory dissection guide. New York: McGraw Hill Education. 152 p.

Weigart, L., and Churchill, E. (1938). The anatomy of the digestive and urogenital systems of the Amphiuma. South Dakota Academy of Science, 18, 16-19. Retrieved April 4, 2015, from