Hint: Scroll valve is the corkscrew-shaped lower portion of the organ that is coiled and is a part of the Gatro-intestinal tract present in fishes like shark, rays, stakes, lungfishes, paddlefish, and sturgeon, etc.
Complete Step by Step Answer:
The corkscrew-shaped lower part of the intestine of the cartilaginous fish is the scroll valve.
A shark's intestines are much shorter than those of humans. By having a spiral valve, or a scroll valve, within the intestine to increase the absorbing surface of the intestine, sharks have compensated for this issue. Maximum nutrient absorption is ensured by maintaining digestible content in the ileum for a prolonged time. Many sharks and related fish eat quite infrequently for this purpose. The food passes almost entirely digested into the shark's comparatively short colon, and then out of the cloaca and vent. The food passes almost entirely digested into the shark's comparatively short colon, and then out of the cloaca and vent.
So, the answer is ‘(b) Intestine of cartilaginous fish.
Cartilaginous fish are fish that, rather than having a bony skeleton, have a skeleton made of cartilage. The cartilaginous fish are all sharks, skates, and rays (for example, the southern stingray).
Cartilaginous fish have gills that open to the ocean through slits, in addition to the disparity in their skeletons with that of bony fish, rather than the bony covering that is found in bony fish. Different shark species can have different numbers of gall slits.
The skin of a cartilaginous fish is covered by placoid scales or dermal denticles, tooth-like scales distinct from the flat scales found on bony fish (called ganoid, ctenoid or cycloid).
- Scroll valves are also known as Spiral valves.
- The spiral valve is internally twisted or coiled to raise the surface area of the intestine, a modification of the ileum, to improve nutrient absorption.
- As a result of the spiral valve constricting the lumen of the ileum, sharks cannot move large hard objects (such as bones) into their lower intestines. Rather, such items remain in the stomach until they are sufficiently broken down or regurgitated to move through the valve area.