Fossil range: Early Silurian - Recent
Great white shark, Carcharodon carcharias
|Subclasses and Orders|
See text. The Silurian is a geologic period and system that extends from the end of the Ordovician period about 443 The great white shark, Carcharodon carcharias, also known as white pointer, white shark, or white death, is an exceptionally large lamniform Chordates ( Phylum Chordata) are a group of Animals that includes the Vertebrates together with several closely related Invertebrates Gnathostomata is the group of Vertebrates with Jaws The group is traditionally a superclass, including the familiar classes of Fish, Thomas Henry Huxley PC FRS (4 May 1825 – 29 June 1895 was an English Biologist, known as "Darwin's Bulldog" for his advocacy This article is about the taxonomic rank for the sequence of species in a taxonomic list see Taxonomic order In scientific classification used
Chondrichthyes or cartilaginous fishes are jawed fish with paired fins, paired nostrils, scales, two-chambered hearts, and skeletons made of cartilage rather than bone. Fish are aquatic Vertebrate animals that are typically ectothermic (previously Cold-blooded) covered with scales, and equipped with two Cartilage is a type of dense Connective tissue. It is composed of specialized cells called chondrocytes that produce a large amount of extracellular matrix Bones are rigid organs that form part of the Endoskeleton of Vertebrates They function to move support and protect the various organs of the body produce They are divided into two subclasses: Elasmobranchii (sharks, rays and skates) and Holocephali (chimaera, sometimes called ghost sharks). Elasmobranchii is the subclass of Cartilaginous fish that includes Skates rays (batoidea, and sharks (selachii. Chimaeras are cartilaginous fish in the order Chimaeriformes.
Animals from this group have a brain weight relative to body size that comes close to that of mammals, and is about 10 times that of bony fishes. Osteichthyes (ˌɒstiːˈɪkθiːz also called bony fish, are a taxonomic Class of Fish that includes the ray-finned fish ( Actinopterygii There are exceptions: the mormyrid bony fish have a relative brain size comparable to humans, while the primitive megamouth shark has a brain of only 0. The family Mormyridae, sometimes called elephantfish, are freshwater fishes native to Africa in the order Osteoglossiformes. The megamouth shark, Megachasma pelagios, is an extremely rare and unusual species of deepwater Shark. 002 percent of its body weight. One of the explanations for their relatively large brains is that the density of nerve cells is much lower than in the brains of bony fishes, making the brain less energy demanding and allowing it to be bigger. Extant cartilaginous fishes range in size from the Dwarf lanternshark, at 16 cm (6. The dwarf lanternshark, Etmopterus perryi, is a shark of the family Dalatiidae found off Colombia and Venezuela, at depths of 3 in), to the Whale Shark, growing to at least 13. The whale shark, Rhincodon typus, is a slow filter feeding Shark that is the largest living Fish Species. 6 m (45 feet).
Their digestive systems have spiral valves, and with the exception of Holocephali, they also have a cloaca. A spiral valve is the lower portion of the intestine of some Sharks rays Skates and Bichirs A modification of the Ileum, In zoological anatomy a cloaca is the posterior opening that serves as the only such opening for the intestinal and urinary tracts of certain animal species
As they do not have bone marrow, red blood cells are produced in the spleen and special tissue around the gonads. Red blood cells are the most common type of Blood cell and the Vertebrate body's principal means of delivering Oxygen to the body tissues via the Blood The spleen is an organ found in all Vertebrate animals In humans the spleen is located in the abdomen of the body where it functions in the destruction of redundant Red The gonad is the organ that makes Gametes The gonads in males are the Testes and the gonads in Females are the Ovaries. They are also produced in an organ called Leydig's Organ which is only found in cartilaginous fishes, although some have lost it. Another unique organ is the epigonal organ which probably has a role in the immune system. The subclass Holocephali, which is a very specialized group, lacks both of these organs. Originally the pectoral and pelvic girdles, which do not contain any dermal elements, did not connect. In later forms, each pair of fins became ventrally connected in the middle when scapulocoracoid and pubioischiadic bars evolved. In rays, the pectoral fins have connected to the head and are very flexible. Batoidea is a Superorder of cartilaginous fish containing more than 500 described species in thirteen families
A spiracle is found behind each eye on most species. Spiracles are small openings on the surface of some Animals that usually lead to Respiratory systems In Elasmobranchs ( Sharks and
Their tough skin is covered with dermal teeth (again with Holocephali as an exception as the teeth are lost in adults, only kept on the clasping organ seen on the front of the male's head), also called placoid scales or dermal denticles, making it feel like sandpaper. Denticles are body surface structures found on some fish and insects Denticles are body surface structures found on some fish and insects In most species, all dermal denticles are oriented in one direction, making the skin feel very smooth if rubbed in one direction and very rough if rubbed in the other. It is assumed that their oral teeth evolved from dermal denticles which migrated into the mouth. But it could be the other way around as the teleost bony fish Denticeps clupeoides has most of its head covered by dermal teeth (as do probably Atherion elymus, another bony fish). Teleostei is one of three infraclasses in class Actinopterygii, the ray-finned fishes The denticle herring ( Denticeps clupeoides) is a small (15 cm species of ray-finned fish found only in the Rivers of Benin, Nigeria This is most probably a secondary evolved characteristic which means there is not necessarily a connection between the teeth and the original dermal scales. The old placoderms did not have teeth at all, but had sharp bony plates in their mouth. The Placodermi were a class of armoured Prehistoric fishes known from Fossils which lived from the late Silurian to the end of the Devonian Thus, it is unknown which of the dermal or oral teeth evolved first. Neither is it sure how many times it has happened if it turns out to be the case. It has even been suggested that the original bony plates of all the vertebrates are gone and that the present scales are just modified teeth, even if both teeth and the body armour have a common origin a long time ago. But for the moment there is no evidence of this.
Chondrichthyes all breathe through 5-7 gills, depending on species. A gill is an anatomical structure found in many aquatic organisms However, they differ on how they get water to pass over the gills. Chondrichthyes mostly use their mouths, as do chimaeras and skates, but rays get water through spiracles, which are small holes on top of their head that run to the gills. Spiracles are small openings on the surface of some Animals that usually lead to Respiratory systems In Elasmobranchs ( Sharks and
Chondrichthyes are ectothermic or cold blooded, meaning they do not have to warm themselves through eating. Cold-blooded organisms (called poikilotherms - "of varying temperature" maintain their body temperatures in ways different from Mammals and Birds Therefore, metabolism is slow as well as the fact that Chondrichthyes members do not have to eat as much. They have no stomach.
Chondrichthyes have toothlike scales called denticles/placoid scales. Denticles are body surface structures found on some fish and insects Denticles provide two functions, protection, and in most cases streamlining. Mucous glands exist in some species as well.
All Chondrichthyes have dorsal, caudal, anal, pelvic, and pectorl fins. Anal, pelvic, and pectoral fins are all paired. Pectoral fines are usually fixed.
The skeleton is cartilaginous. The notochord, which is present in the young, is gradually replaced by cartilage. The notochord is a flexible rod-shaped body found in Embryos of all Chordates It is composed of cells derived from the Mesoderm and defines the Chondrichthyes also lack ribs, so in the event that they leave the water, they're own body weight will crush their internal organs long before they would suffocate.
Fertilization is internal. Development is usually live birth (ovoviviparous species) but can be through eggs (oviparous). Ovoviviparous Animals develop within eggs that remain within the mother's body up until they hatch or are about to hatch Oviparous animals are animals that lay eggs, with little or no other Embryonic development within the mother Some rare species are viviparous. A viviparous Animal is an animal employing vivipary: the embryo develops inside the body of the mother as opposed to outside in an egg ( Ovipary There is no parental care after birth, however, some Chondrichthyes do guard their eggs.