Chordates

Phylum Chordata is a group of highly developed animals, including more than 75,000 living species.

The characteristic features of chordates are the presence of notochord, nerve cord and pharyngeal gill slits. Out of these three, only nerve cord persists during whole life of an organism, whereas gill-slits disappear entirely during the embryonic stage and notochord gets replaced by a vertebral column.

Higher chordates are bilaterally symmetrical, triploblastic and coelomate. These animals possess organ system level of organisation, closed circulatory system, ventrally located heart, well developed hepatic portal system and a muscular post anal tail.

Phylum Chordata is divided into four sub-phylums namely, Hemichordata, Urochordata, Cephalochordata and Vertebrata. Urochordata and Cephalochordata are very primitive forms and are regarded as Protochordates.

Sub-phylum Hemichordata is a group of marine, tube-dwelling worm-like animals.They possess characters of both vertebrates and invertebrates.Balanoglossus and Saccoglossus are common hemichordates.

Organisms belonging to sub-phylum Urochordata possess notochord and nerve cord in the tail region only.They are also called Tunicata or Ascidians. Pyrosome and Doliolum are common urochordates.

Sub-phylum Cephalochordata is a group of marine animals in which notochord persists throughout their life. Amphioxus is a common cephalochordate.

Organisms belonging to sub-phylum Vertebrata have a notochord replaced by backbone or vertebral column which forms the main axis of the internal skeleton.

On the basis of the presence or absence of jaws, this subphylum is classified into twosuper classes; namely, Agnatha and Gnathostomata.

Gnathostomata is further classified into Pisces and Tetrapoda.

Pisces is classifiedfurther into Chondrichthyes (include cartilaginous fish) and Osteichthyes (include bony fish).

Chondrichthyes are mostly marine and cold blooded fish. Their skeleton is made up of cartilage.Scoliodon(shark) is a common cartilaginous fish.

Osteichthyes are both freshwater and marine fish that are also cold blooded. Their skeleton is made up of bones.Labio rohita(Rohu) is a common bony fish.

Tetrapoda is classified further into amphibia, reptilia, aves and mammalia.

Amphibians are cold blooded animalswhich can live both on land and water. Frogs, salamander, etc., are common amphibians.

Reptilia are cold blooded animals that live on land. Lizards, snakes, etc., are common reptiles.

Aves are warm-blooded animals with streamlined body and feathers which help them to fly. All the birds like crow, sparrow, etc., are categorised under this class.

Mammals are viviparous animals that possess mammary glands to feed their young ones. Human beings, monkeys, etc., are terrestrial mammals, while whales are aquatic mammals.

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  • Q1

    Name two classes of Chordata which are homothermal.

    Marks:1
    Answer:

    The two classes of Chordata which are homothermal are:}
    a) Aves
    b) Mammalia

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  • Q2

    Name the poisonous lizard whose venom or poison can kill a human.

    Marks:1
    Answer:

    Heloderma (Gila monster) is the poisonous lizard whose venom or poison can kill a human.

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  • Q3

    Name any two flightless birds.

    Marks:1
    Answer:

    The two flightless birds are:
    a) Penguin
    b) Kiwi

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  • Q4

    Name the vertebrate class which requires two different habitats to complete their life cycle.

    Marks:1
    Answer:

    Amphibian, is the vertebrate class which requires two different habitats to complete their life cycle.

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  • Q5

    Name the reptile that has four chambered heart.

    Marks:1
    Answer:

    Crocodile is the reptile that has four chambered heart.

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