fish coprolite

The heteropolar form spiral wound of this coprolite is the result of the spiral valve, characteristic of species of archaic origin.

The spiral valve It is an internal organ of the sharks, stripes, sturgeons and cyclostomes. It is formed by membranous folds on the internal walls of the small intestine arranged in a spiral shape and is snail-shaped. In sharks and rays, it begins just behind the stomach, connects to the colon and finally to the cloaca. Its function is to reduce the speed of circulation of chyme in the ileum, which increases the duration of digestion and at the same time, increases the surface area for nutrient absorption without the need to lengthen the intestine, as is the case in mammals. For this reason, many sharks and related fish feed very infrequently. This example of space optimization has the disadvantage that the slow circulation of food favors the presence of internal parasites.