Chordates are animals possessing a notochord, a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail for at least some period of their life cycles. Of the more than 75,000 living species of chordates, about half are bony fish of the class Osteichthyes. The world's largest and fastest animal, the blue whale and peregrine falcon, respectively, are chordates, as are humans.
Physeter macrocephalus (Sperm Whale)
The sperm whale has the longest intestinal system in the world, exceeding 300 m in larger specimens. The sperm whale has four stomachs. The first secretes no gastric juices and has very thick muscular walls to crush the food (since whales can't chew) and resist the claw and sucker attacks of swallowed squid. The second stomach is larger and is where digestion proper takes place. Undigested squid beaks accumulate in the second stomach – as many as 18,000 have been found in some dissected specimens.
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Crotalus tigris (Tiger rattlesnake)
As the tiger rattlesnake eats, the food is pushed from the mouth into the esophagus. The food then enters the stomach where most of the digestion occurs. The stomach secretes gastric juices and digestive enzymes that break down the prey. Once most of the digestion is completed, it passes into the small intestine. The snake absorbs most of its nutrients from the food once it enters the small intestine. In addition, the liver and pancreas secrete more digestive enzymes into the small intestine to finish breaking down prey for absorption. Once the food travels through the small intestine, it enters the large intestine where much of the remaining water is reabsorbed.
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Alligator mississippiensis (American alligator)
The alligator has teeth that are adapted for seizing and holding prey, and food is swallowed without being chewed. The digestive tract is relatively short, as meat is a fairly simple substance to digest. The stomach is divided into two parts: a muscular gizzard that grinds food, and a digestive chamber where enzymes work on it. The stomach is more acidic than that of any other vertebrate and contains ridges for stomach stones, which play a role in the mechanical breakdown of food. Interestingly, digestion takes place more quickly at higher
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