Ncert Biology Chapter 4
Ncert Biology Chapter 4
Ncert Biology Chapter 4
CHAPTER 4
ANIMAL KINGDOM
4.1 Basis of When you look around, you will observe different animals with different
Classification structures and forms. As over a million species of animals have been
described till now, the need for classification becomes all the more
4.2 Classification of
important. The classification also helps in assigning a systematic position
Animals to newly described species.
4.1.2 Symmetry
Animals can be categorised on the basis of their
symmetry. Sponges are mostly asymmetrical,
i.e., any plane that passes through the centre
does not divide them into equal halves. When
any plane passing through the central axis of
the body divides the organism into two identical
halves, it is called radial symmetry. Figure 4.1 (b) Bilateral symmetry
Coelenterates, ctenophores and echinoderms
have this kind of body plan (Figure 4.1a).
Animals like annelids, arthropods, etc., where Ectoderm
Mesoglea
the body can be divided into identical left and Endoderm
right halves in only one plane, exhibit bilateral
symmetry (Figure 4.1b).
Those animals in which the developing embryo has a third germinal layer,
mesoderm, in between the ectoderm and endoderm, are called
triploblastic animals (platyhelminthes to chordates, Figure 4.2b).
Coelom Pseudocoelom
4.1.4 Coelom
Presence or absence of a cavity between the body
wall and the gut wall is very important in
classification. The body cavity, which is lined
by mesoderm is called coelom. Animals
possessing coelom are called coelomates, e.g.,
annelids, molluscs, arthropods, echinoderms,
(a) (b) hemichordates and chordates (Figure 4.3a). In
some animals, the body cavity is not lined by
mesoderm, instead, the mesoderm is present as
scattered pouches in between the ectoderm and
endoderm. Such a body cavity is called
pseudocoelom and the animals possessing them
are called pseudocoelomates, e.g.,
(c) aschelminthes (Figure 4.3b). The animals in
Figure 4.3 Diagrammatic sectional view of : which the body cavity is absent are called
(a) Coelomate (b) Pseudocoelomate acoelomates, e.g., platyhelminthes (Figure 4.3c).
(c) Acoelomate
4.1.5 Segmentation
In some animals, the body is externally and internally divided into
segments with a serial repetition of at least some organs. For example, in
earthworm, the body shows this pattern called metameric segmentation
and the phenomenon is known as metamerism.
4.1.6 Notochord
Notochord is a mesodermally derived rod-like structure formed on the
dorsal side during embryonic development in some animals. Animals with
notochord are called chordates and those animals which do not form this
structure are called non-chordates, e.g., porifera to echinoderms.
Figure 4.4 Broad classification of Kingdom Animalia based on common fundamental features
(a) (b)
Figure 4.6 Examples of Coelenterata indicating outline of their body form :
(a) Aurelia (Medusa) (b) Adamsia (Polyp)
(a) (b)
Figure 4.9 Examples of Platyhelminthes : (a) Tape worm (b) Liver fluke
52 BIOLOGY
Figure 4.11 Examples of Annelida : (a) Nereis Examples : Nereis, Pheretima (Earthworm) and
(b) Hirudinaria Hirudinaria (Blood sucking leech).
ANIMAL KINGDOM
ANIMAL KINGDOM 35
53
Vertebrata
Division
Agnatha Gnathostomata
(lacks jaw) (bears jaw)
Super Class
Pisces Tetrapoda
(bear fins) (bear limbs)
Figure 4.22 Reptiles : (a) Chameleon (b) Crocodilus (c) Chelone (d) Naja
Figure 4.23 Some birds : (a) Neophron (b) Struthio (c) Psittacula (d) Pavo
(c)
(a)
(d)
(b)
Figure 4.24 Some mammals : (a) Ornithorhynchus (b) Macropus (c) Pteropus (d) Balaenoptera
60 BIOLOGY
Tissue Radial Absent Absent Incomplete Absent Absent Comb plates for
Ctenophora
locomotion.
Organ &
Platyhelm- Organ- Bilateral Absent Absent Incomplete Absent Absent Flat body, suckers.
inthes system
Organ- Pseudo Often worm-
Aschelmin Bilateral coelo- Absent Complete Absent Absent shaped,
system
thes mate elongated.
Organ- Coelo- Body segment
Annelida system Bilateral mate Present Complete Present Present ation like rings.
Organ- Exoskeleton of cu-
Bilateral Coelo- Present Complete Present Present
ticle, jointed ap-
Arthropoda system mate
pendages.
Organ- Bilateral Coelo- Absent Complete Present Present External skeleton
Mollusca system mate shell usually
present.
SUMMARY
EXERCISES
1. What are the difficulties that you would face in classification of animals, if common
fundamental features are not taken into account?
2. If you are given a specimen, what are the steps that you would follow to classify
it?
3. How useful is the study of the nature of body cavity and coelom in the
classification of animals?
4. Distinguish between intracellular and extracellular digestion?
5. What is the difference between direct and indirect development?
6. What are the peculiar features that you find in parasitic platyhelminthes?
7. What are the reasons that you can think of for the arthropods to constitute the
largest group of the animal kingdom?
8. Water vascular system is the characteristic of which group of the following:
(a) Porifera (b) Ctenophora (c) Echinodermata (d) Chordata
9. “All vertebrates are chordates but all chordates are not vertebrates”. Justify the
statement.
10. How important is the presence of air bladder in Pisces?
11. What are the modifications that are observed in birds that help them fly?
12. Could the number of eggs or young ones produced by an oviparous and viviparous
mother be equal? Why?
13. Segmentation in the body is first observed in which of the following:
(a) Platyhelminthes (b) Aschelminthes (c) Annelida (d) Arthropoda
14. Match the following:
(i) Operculum (a) Ctenophora
(ii) Parapodia (b) Mollusca
(iii) Scales (c) Porifera
(iv) Comb plates (d) Reptilia
(v) Radula (e) Annelida
(vi) Hairs (f) Cyclostomata and Chondrichthyes
(vii) Choanocytes (g) Mammalia
(viii) Gill slits (h) Osteichthyes
15. Prepare a list of some animals that are found parasitic on human beings.