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Digestive Anatomy
Spiral Valve (Sharks & Rays)
Valvula spiralis
A corkscrew-shaped fold inside the intestines of sharks, rays, and primitive bony fish - dramatically increases surface area in a short gut.
Region: Trunk Unique to: cartilaginous
📖 Overview
Because cartilaginous fish generally have short, straight intestines, they solve the surface-area problem with an internal spiral: the gut wall folds into a helical or scroll-shaped structure that food must traverse before reaching the cloaca. Sturgeon, gars, and lungfish retain this ancestral feature; teleosts have replaced it with an elongated coiled gut.
⚙️ Function
Increases digestive surface area 4-10x compared to a straight tube, allowing nutrient absorption in a compact body.
✨ Fun Fact
The spiral valve of some shark species has 40+ turns of tissue coiled into just 10-15 cm of intestine - a natural engineering marvel.
🔗 Related Digestive Structures