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Tuatara: Volume 1, Issue 3, September 1948

Inflation of the Abdomen in Cephaloscyllium

page 39

Inflation of the Abdomen in Cephaloscyllium

The porcupine fish and its allies are well-known for their ability to inflate themselves. Less well-known is the fact that sharks of the Genus Cephaloscyllium also possess this ability, so much so that in parts of the world the members of this genus are commonly known as “swell-sharks”. In this respect, they are unique among elasmobranchs. The Australasian literature dealing with Cephaloscyllium isabellum, the carpet-shark and the common species of this genus in our waters, contains peculiar and contradictory statements on the method by which this shark inflates its abdomen with water or, when taken from the water, with air.

Eugenie Clark (1), of the New York Zoological Society, has recently described the nature of the mechanism involved in the inflation of the abdomen in the closely related Cephaloscyllium uter. Here he finds that, as usual in sharks, the stomach is divided into two regions: the cardiac region which is attached to the oesophagus, and the pyloric region which follows the cardiac stomach and opens into the intestine. In C. uter, air or water is gulped into the cardiac portion of the stomach and stored there since this portion of the stomach can be closed off from the oesophagus by a strong sphincter muscle, and from the pyloric portion of the stomach by a second sphincter muscle. Air or water cannot pass beyond the second sphincter and escape into the intestine. The cardiac portion of the stomach is not attached ventrally to the body-wall. As it fills, this portion of the stomach is free to extend in all directions.

1. CLARK, EUGENIE. Notes on the inflating power of the swell-shark, Cephaloscyllium uter. Copeia, 1947 (4): 278-280.