Bizarrely, many species of animals, such as the carp and platypus, lost their stomachs in the evolutionary past, and new research suggests they may never evolve the organs back.
The stomach is the part of the gut where the main part of digestion takes place. Glands in this organ secrete enzymes known as pepsins, which break down proteins, and strong acids that soften food and help the enzymes work. The glands first appeared about 450 million years ago, and they represent an evolutionary innovation found exclusively in jawed creatures with backbones.
Surprisingly, the gastric glands that define the stomach are missing in a number of jawed vertebrates. In 1805, the French zoologist Georges Cuvier discovered that many teleosts, or the largest living group of fish, such as the carp family, lack stomachs. The past 200 years of research suggests that up to 27 percent, speaking conservatively, of all teleost species may lack stomachs. Primitive bony fish such as lungfish and some cartilaginous fish such as chimeras lost the organs as well…
The spotted ratfish aka spotted chimera, Hydrolagus colliei, can be found off the coast of California to depths of about 3,000 feet. Its common name comes from the white spots that cover its body and its pointed rat-like tail. These fish are chimeras, meaning they have characteristics of bony fishes and sharks, from which they descended millions of years ago.
While exploring the debris slope of the collapsed side of the underwater volcano Kick’em Jenny near Grenada in the Caribbean, the Nautilus expedition crew had a surprising find of a large cold methane seep and rich biology around it. Here are a few of the amazing creatures we spotted there and more can be found at http://www.nautiluslive.org.
Shovelnose Chimera, swimming sea cucumber, deep sea octopus, unidentified species of Snailfish.
Chimaeras are perhaps the oldest and most enigmatic groups of fishes alive today. Their closest living relatives are sharks, but their evolutionary lineage branched off from sharks nearly 400 million years ago, and they have remained an isolated group ever since. Like sharks, chimaeras have skeletons composed of cartilage and the males have claspers for internal fertilization of females.
Unlike sharks, male chimaeras also have retractable sexual appendages on the forehead and in front of the pelvic fins and a single pair of gills. Most species also have a mildly venomous spine in front of the dorsal fin.
Chimaeras were once a very diverse and abundant group, as illustrated by their global presence in the fossil record. They survived through the age of dinosaurs mostly unchanged, but today these fishes are relatively scarce and are usually confined to deep ocean waters, where they have largely avoided the reach of explorers and remained poorly known to science.
Chimaeras are the only vertebrates to retain traces of a third pair of limbs.
Dive 12, August 13, Northeast U.S. Canyons Expedition 2013
A chimaera swims lazily a couple meters above the seafloor in Lydonia Canyon. Chimeras, sometimes called Ghost Sharks or ratfishes, are a group of cartilaginous fishes, elasmobranchs, along with sharks and rays. Many species, such as this one, are dwellers of the deep ocean.
10 More Cool Sharks You Probably Don’t Hear Much About During Shark Week
So I know that Shark Week is over now, but I couldn’t just stop at 10, so here are 10 more!
Angel Shark (Squatina) There are 23 different species of angel shark and all live in shallow, warm seas, though some migrate to warmer waters during the summer. Most types grow to a length of 5 ft (1.5 m). They hunt at night in their own territories. Unlike rays, they have sharp teeth for feeding on shelled prey and small fish. They disguise themselves from prey by covering their bodies in sand and often having sandy-colored skin. An angel shark is hard to see as it lies on the seabed. Its body is so flat that it appears no more than a low mound in the sand. Unlike a ray, it uses its tail rather than its large fins to swim. Read more about this shark…(read more)
Chimaeras are most closely related to sharks, although their evolutionary lineage branched off from sharks nearly 400 million years ago, and they have remained an isolated group ever since. Like sharks, chimaeras are cartilaginous and have no real bones. The lateral lines running across this chimaera are mechano-receptors that detect pressure waves (just like ears). The dotted-looking lines on the frontal portion of the face (near the mouth) are ampullae de lorenzini and they detect perturbations in electrical fields generated by living organisms.
This image was captured at the 'Zona Senja' site near Sulawesi, Indonesia, on August 2, 2010.
Image courtesy of NOAA Okeanos Explorer Program, INDEX-SATAL 2010.
Eerie critters from the deep sea: Predators and Scavengers
For Halloween 2012, deep-sea animals eating or scavenging for food. In order of appearance: Black ghost shark eating a dead fish, galaxy siphonophore digesting a live fish, crab scavenging a whale bone, comb jelly eating another comb jelly (footage courtesy of NHK), small octopus hunting, black-eye squid feeding on a juvenile, Humboldt squid eating squid hatchlings.
This crazy looking fish is called a deep-water chimaera, but it’s not a mythical beast: it’s also called a small-eyed rabbitfish and is related to sharks. It can be found at depths of up to 3000 meters (9800 feet) on the mid-Atlantic ridge.
This one was found there on a trip with the Census of Marine Life. Read more about the Census here - ocean census
Not to be confused with the Rabbitfish, a group of brightly-colored reef-dwellers.
The rat fish is one of the few fish of the order Chimaeriformes that you can see in person. Though a member of an order that dwells up to 2600 meters (8500 feet) below the surface of the ocean, they are capable of living at surface-level relatively easily, and as such are one of the only Chimaeridae (also known as ghost sharks or ghost fish) that are kept in public aquariums.
Chimaera are the closest living relatives to sharks, though they diverged over 400 million years ago. We have abundant fossil evidence of their evolution to their current forms, and they’re one of the most-studied orders of cartilaginous fish. These fish are the only vertebrates to retain vestigial evidence of a third set of limbs.
Illustrations de Ichtyologie ou histoire naturelle générale et particulière des Poissons. Marcus Elieser Bloch et al., 1795.