They have a intestinal spiral valve rather than a true stomach.

The spiral valves of Heister are supported by underlying smooth muscle fibers.

In lampreys, the spiral valve is extremely small, possibly because their diet requires little digestion.

By the time the yolk is fully utilized, a spiral valve has developed in the intestine and the fish starts to feed.

At this time, the embryo has well-developed external gills and a spiral valve intestine.

The term spiral valve may refer to:

It contains 'spiral valves of Heister,' which do not provide much resistance to the flow of bile.

This short length is achieved by the spiral valve with multiple turns within a single short section instead of a very long tube-like intestine.

Additional parasites that may be found in this ray's spiral valve intestine include Eimeria chollaensis sp.

The small intestine contains an internal partition shaped like a corkscrew, called a spiral valve, which increases the surface area available for food absorption.

A spiral valve is the lower portion of the intestine of some sharks, rays, skates and bichirs.

Hagfish have no spiral valve at all, with digestion occurring for almost the entire length of the intestine, which is not subdivided into different regions.

Amussat's valves: Spiral valves within the cystic duct.

A known parasite of this species is the tapeworm Oncomegoides celatus, which infests the spiral valve intestine.

The longhead catshark is unique among Apristurus species in that the duodenum is not short but almost as long as the spiral valve intestine.

Also, whilst dung can be formed in a spiral (notably sharks due to their digestive system's spiral valve), the consistency of Dinocochlea makes this unlikely.

Spiral valves of Heister are undulating folds or valves in the proximal mucosa of the cystic duct.

A modification of the ileum, the spiral valve is internally twisted or coiled to increase the surface area of the intestine, to increase nutrient absorption.

Sharks have compensated for this problem by having a spiral valve, or a scroll valve, inside the intestine to increase the absorbent surface of the intestine.

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.

His name is lent to the plant genus Heisteria, as well as to the spiral valves of Heister, defined as anatomical folds of the cystic duct.

The spiral valve is essential to keeping the mixing of the two types of blood to a minimum, enabling the animal to have higher metabolic rates, and be more active than otherwise.

Furthermore, the conus arteriosus has lost its original valves and contains a spiral valve, instead, that divides it into two parallel parts, thus helping to keep the two bloodstreams separate.

The blurred lanternshark is very similar to the smooth lanternshark, but is larger and can be reliably differentiated by the number of turns in the spiral valve intestine (16-19 versus 10-13).