The spiral valve is formed by twisting the internal growths of the wall of the large intestine (sharks) or the posterior part of the middle intestine (sturgeons); it serves to increase the suction surface of the intestine (sharks, rays, sturgeons).
It is particularly developed in sharks and rays. In these fish, the length of the intestine is short: for example, in 3m long sharks it is only 2.7m (in humans about 8m), so the spiral valve greatly increases the suction surface of the intestine. This organ greatly slows the passage of food through the intestine, increasing the time it takes to ingest it. In sharks and rays, the stomach usually opens almost immediately into the spiral valve, which in turn opens into the rectum. The highly developed spiral valve is one of the most characteristic anatomical features of sharks and rays.
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