Invertebrates and Non-chordates

There is a huge variety of animalsfound on the earth and they show a large number of common characteristics.
Scientists group them on the basis of their similarities and dissimilarities by the system of classification.

R.H. Whittaker introduced five-kingdom classification system to classify all the living organisms into five different kingdoms; namely, Monera, Protista, Fungi, Plantae and Animalia.

The animal kingdom includes all the multicellular and eukaryotic organisms which lack cell wall and chlorophyll. Due to the lack of chlorophyll, they follow heterotrophic mode of nutrition.

The organisms of this kingdom are classified further on the basis of type of symmetry, number of germ layers, coelom and notochord present in them.

Animals can be broadly classified into chordates and non-chordates on the basis of presence or absence of a notochord, respectively.

Non- chordates are further divided into sub phyla; namely, Porifera, Coelenterata, Platyhelminthes, Aschelminthes, Annelida, Arthropoda, Mollusca andEchinodermata.

Poriferans are the simplest type of multicellular animals. They are pore-bearing and usually asymmetrical. Sycon and Euspongiaare some common poriferans.

Coelentrates are mostly marine and radially symmetrical animals. They possess specialised tentacles that help to capture the prey. Hydra and sea anemone are some common coelenterates.

Hydra is a coelenterate with small, hollow and cylindrical body with a sticky basal disc for attachment. It possesses six to eight tentacles to capture the prey. It shows two types of locomotion: looping and somersaulting. It reproduces by budding and regeneration.

Platyhelminthes includes flat worms which are dorsoventrally flattened, soft, acoelomate and bilaterally symmetrical organisms. Tapeworm and liver fluke are some commonplatyhelminthes.

Aschelminthesare often worm shaped which are bilaterally symmetrical, triploblastic, pseudocoelomate and un-segmented animals. Ascaris and Wuchereriaare some commonaschelminthes.

Annelids include triploblastic, metamerically segmented, coelomate worms with a thin flexible coating around the body. Earthworm and leech are some common annelids.

Earthworm is an annelid with long andcylindrical body that is divided into series of 80-100 ring-like segments (pre-clitellum, clitellum and post-clitellum segments). It lacks head, eyes, tail or legs. It is also known as ‘farmer’s friend’ as it helps in improving soil fertility.

Arthropods include animals which have jointed appendages, segmented body that is divisible into head, thorax and abdomen; and possess hard exoskeleton of chitin. Cockroach and scorpion are some common arthropods.

Molluscs include soft bodied, triploblastic animals that are usually surrounded by an outer hard covering of hard shell. Snail and slug are some common molluscs.

Ehchinoderms include spiny skinned free living marine animals. Star fish and sea urchin are some common echinoderms.

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  • Q1

    Name an invertebrate that shows radial symmetry.

    Marks:1
    Answer:

    Star fish shows radial symmetry.

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  • Q2

    Name any one invertebrate with incomplete alimentary canal.

    Marks:1
    Answer:

    Platyhelminthes is one of the invertebrate with incomplete alimentary canal.

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  • Q3

    Name the type of coelom that lies between mesoderm and endoderm.

    Marks:1
    Answer:

    Pseudocoelom is the type of coelom that lies between mesoderm and endoderm.

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  • Q4

    Name the symmetry that divides the body into several equal parts like the spokes of a wheel.

    Marks:1
    Answer:

    Radial symmetry divides the body into several equal parts like spokes of wheel.

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  • Q5

    Name the cavity found between the body wall and gut of an animal.

    Marks:1
    Answer:

    Coelom is the cavity found between the body wall and the gut of an animal.

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