Spiral valve

A spiral valve or scroll valve is the corkscrew-shaped lower portion of the intestine of some sharks, Acipenseriformes (sturgeon and paddlefish), rays, skates, bichirs, Lepisosteiformes (gars), and lungfishes.

By keeping digestible material in the ileum for an extended period maximum nutrient absorption is ensured.

The food passes into the comparatively short colon of the shark almost fully digested, and then out the cloaca and vent.

A consequence of the spiral valve constricting the lumen of the ileum is that sharks cannot pass large hard objects (such as bones) through their lower intestine.

Such objects instead remain in the stomach until sufficiently broken down for passing through the valve region, or are regurgitated.