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The term chordata is originated by two words of greek language, the chorda and the ata.

Although phylum chordata includes a lesser number of species as compared to non- chordates, yet chordates show advanced evolutionary characters. This phylum derives its name from a structure, named notochord and surely classifies Homo sapiens under its domain. The term chordata is originated by two words of greek language, the chorda and the ata. Meaning of ‘chorda’ is a thick string and the meaning of ‘ata’ is to have an overall meaning of chordata is animals having notochords. Notochord supports the body of these animals. so, chordates are the animals in which notochord is present in any stage of their life-span. Animals which do not have notochord are known as non- chordates. In chordates, species of maximum live animals is Pisces group and minimum live animals is Amphibia.

Phylum: Chordates Class: Chondrichthyes

This class includes Cartilaginous fishes and they are marine in nature. Their endoskeleton is made up of cartilage and notochord is persistent throughout life. Exoskeleton over the skin is made up of placoid scales and these scales are like denticles and originate from dermis of skin. Their teeth are modified placoid scales, which are backwardly directly. In these fishes, 5-7 pairs of gills are present, which open directly outside the body by gill slits. Operculum is normally absent in these fishes. In them the mouth is present at the ventral surface of the head. Jaws and teeth are present. Suspensorium of jaws is Hyalostylic type. Their Jaws are very powerful and animals are predaceous in nature. Air bladder and lungs are absent in them, as they have to swim constantly to avoid sinking. A spiral valve and croll valve is found in their intestine to increase surface area along with this cloacal aperture is also present. Their liver is mainly bilobed. There is a special structure at the dorsal surface of the head in these fishes, which is called “ Ampullae of Lorenzini” that works as a thermoreceptor. Genital duct of these organisms open into the cloacal aperture. Mode of fertilization is internal as male fishes have “claspers” as copulatory organs, which are developed by inner edges of pelvic fins. Most of them are Viviparous in nature.

Phylum: Chordata Class: Osteichthyes

This mainly includes bony fish. Fishes of this class are found in freshwater as well as marine water. Endoskeleton of these fishes are made up of bones, so these are called bony fishes. Their exoskeleton is made up of scales, which may be cycloid or ctenoid or ganoid type. Placoid scales are absent. In these types of fishes respiration occurs by 4- gills. These gills are covered by an operculum at each side of the body. Their mouth is normally terminal or subterminal, teeth are found in jaws. Suspensorium of the jaw is autostylic.Helping respiratory organs in them is mainly air bladders. Lung fishes respire through air bladders. In other fishes these air bladders are hydrostatic i.e help in maintaining balance of body and provide buoyancy. Spiracle is absent in them along with the scroll valve of the intestine. Cloaca is absent, in place of cloacal aperture annus is present also no ampulla of Lorenzini. Their liver is trilobed and their tail is normally homocercal type but sometimes it may be diphycercal type. Fishes are oviparous but may be ovoviviparous or viviparous.

Ans. Few features of chordates are:

Ans. Chondrichthyes  include Cartilaginous fishes and they are marine in nature. Their endoskeleton is made up of cartilage and notochord is persistent throughout life. Exoskeleton over the skin is made up of placoid scales and these scales are like denticles and originate from dermis of skin. Their teeth are modified placoid scales, which are backwardly directly. In these fishes, 5-7 pairs of gills are present, which open directly outside the body by gill slits. Operculum is normally absent in these fishes. In them the mouth is present at the ventral surface of the head. Jaws and teeth are present. Suspensorium of jaws is Hyalostylic type. Their Jaws are very powerful and animals are predaceous in nature. Air bladder and lungs are absent in them, as they have to swim constantly to avoid sinking.

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They are both fresh water as well as marine.

Endoskeleton is made up of cartilage.

Exoskeleton is made up of cycloid scales.

Exoskeleton is made up of Placoid scale.

They are ovoviviparous or viviparous.

They are both fresh water as well as marine.

Endoskeleton is made up of cartilage.

Exoskeleton is made up of cycloid scales.

Exoskeleton is made up of Placoid scale.

They are ovoviviparous or viviparous.