46 BIOLOGY

e d
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T s
HAPTER

h
A K
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NIMAL INGDOM

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4.1 Basis of When you look around, you will observe different animals with different

p
Classification structures and forms. As over a million species of animals have been

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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.

© e 4.1 BASIS OF CLASSIFICATION

b
Inspite of differences in structure and form of different animals, there are

o
fundamental features common to various individuals in relation to the
arrangement of cells, body symmetry, nature of coelom, patterns of

t
digestive, circulatory or reproductive systems. These features are used

t
as the basis of animal classification and some of them are discussed here.

o
4.1.1 Levels of Organisation

n
Though all members of Animalia are multicellular, all of them do not
exhibit the same pattern of organisation of cells. For example, in sponges,
the cells are arranged as loose cell aggregates, i.e., they exhibit cellular
level of organisation. Some division of labour (activities) occur among
the cells. In coelenterates, the arrangement of cells is more complex. Here
the cells performing the same function are arranged into tissues, hence is
called tissue level of organisation. A still higher level of organisation, i.e.,
organ level is exhibited by members of Platyhelminthes and other higher
phyla where tissues are grouped together to form organs, each specialised
for a particular function. In animals like Annelids, Arthropods, Molluscs,
ANIMAL KINGDOM
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74

Echinoderms and Chordates, organs have

associated to form functional systems, each
system concerned with a specific physiological
function. This pattern is called organ system
level of organisation. Organ systems in different
groups of animals exhibit various patterns of
complexities. For example, the digestive system

d
in Platyhelminthes has only a single opening

e
to the outside of the body that serves as both
mouth and anus, and is hence called

h
incomplete. A complete digestive system has
two openings, mouth and anus. Similarly, the

T s
Figure 4.1 (a) Radial symmetry

i
circulatory system may be of two types:

R l
(i) open type in which the blood is pumped
out of the heart and the cells and tissues are

E b
directly bathed in it and

u
(ii) closed type in which the blood is circulated

C
through a series of vessels of varying diameters

p
(arteries, veins and capillaries).

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4.1.2 Symmetry
Animals can be categorised on the basis of their

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symmetry. Sponges are mostly asymmetrical,
i.e., any plane that passes through the centre

b
does not divide them into equal halves. When
any plane passing through the central axis of
the body divides the organism into two identical

o
halves, it is called radial symmetry. Figure 4.1 (b) Bilateral symmetry

t
Coelenterates, ctenophores and echinoderms
have this kind of body plan (Figure 4.1a).

t
Animals like annelids, arthropods, etc., where Ectoderm
Mesoglea

o
the body can be divided into identical left and Endoderm
right halves in only one plane, exhibit bilateral

n
symmetry (Figure 4.1b).

4.1.3 Diploblastic and Triploblastic

Organisation
Animals in which the cells are arranged in two
embryonic layers, an external ectoderm and
Mesoderm
an internal endoderm, are called diploblastic (a) (b)
animals, e.g., coelenterates. An undifferentiated
layer, mesoglea, is present in between the Figure 4.2 Showing germinal layers :
ectoderm and the endoderm (Figure 4.2a). (a) Diploblastic (b) Triploblastic
 48 BIOLOGY

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).

4.1.4 Coelom
Presence or absence of a cavity between the body

d
wall and the gut wall is very important in

e
classification. The body cavity, which is lined
by mesoderm is called coelom. Animals

h
possessing coelom are called coelomates, e.g.,

T s
annelids, molluscs, arthropods, echinoderms,

i
hemichordates and chordates (Figure 4.3a). In

R l
some animals, the body cavity is not lined by

b
mesoderm, instead, the mesoderm is present as

E
scattered pouches in between the ectoderm and

u
endoderm. Such a body cavity is called

C p
pseudocoelom and the animals possessing them

N re
are called pseudocoelomates, e.g.,
aschelminthes (Figure 4.3b). The animals in
Figure 4.3 Diagrammatic sectional view of : which the body cavity is absent are called

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(a) Coelomate (b) Pseudocoelomate acoelomates, e.g., platyhelminthes (Figure 4.3c).
(c) Acoelomate

b
4.1.5 Segmentation
In some animals, the body is externally and internally divided into

o
segments with a serial repetition of at least some organs. For example, in

t
earthworm, the body shows this pattern called metameric segmentation
and the phenomenon is known as metamerism.

o t 4.1.6 Notochord
Notochord is a mesodermally derived rod-like structure formed on the

n
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.

4.2 CLASSIFICATION OF ANIMALS

The broad classification of Animalia based on common fundamental

features as mentioned in the preceding sections is given in Figure 4.4.
ANIMAL KINGDOM
ANIMAL KINGDOM 49
94

e d
T s h
R li
E u b
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Figure 4.4 Broad classification of Kingdom Animalia based on common fundamental features

N re p
The important characteristic features of the
different phyla are described.

4.2.1 Phylum – Porifera

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Members of this phylum are commonly known
as sponges. They are generally marine and mostly

b
asymmetrical animals (Figure 4.5). These are
primitive multicellular animals and have cellular

o
level of organisation. Sponges have a water

t
transport or canal system. Water enters through
minute pores (ostia) in the body wall into a central

t
cavity, spongocoel, from where it goes out
through the osculum. This pathway of water

o
transport is helpful in food gathering, respiratory (b)
exchange and removal of waste. Choanocytes

n
(a)
or collar cells line the spongocoel and the canals.
Digestion is intracellular. The body is supported
by a skeleton made up of spicules or spongin
fibres. Sexes are not separate (hermaphrodite),
i.e., eggs and sperms are produced by the same
individual. Sponges reproduce asexually by
fragmentation and sexually by formation of
gametes. Fertilisation is internal and development (c)
is indirect having a larval stage which is Figure 4.5 Examples of Porifera : (a) Sycon
morphologically distinct from the adult. (b) Euspongia (c) Spongilla
 50 BIOLOGY

Examples: Sycon (Scypha), Spongilla (Fresh water sponge) and Euspongia

(Bath sponge).

4.2.2 Phylum – Coelenterata (Cnidaria)

They are aquatic, mostly marine, sessile or free-swimming, radially
symmetrical animals (Figure 4.6). The name cnidaria is derived from the

e d
T s h
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C
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(a) (b)
Figure 4.6 Examples of Coelenterata indicating outline of their body form :

b
(a) Aurelia (Medusa) (b) Adamsia (Polyp)

cnidoblasts or cnidocytes (which contain the stinging capsules or

o
nematocytes) present on the tentacles and the body. Cnidoblasts are used

t
for anchorage, defense and for the capture of prey (Figure 4.7). Cnidarians

t
exhibit tissue level of organisation and are diploblastic. They have a central
gastro-vascular cavity with a single opening, mouth on hypostome.

o
Digestion is extracellular and intracellular. Some of the cnidarians, e.g.,

n
corals have a skeleton composed of calcium carbonate. Cnidarians exhibit
two basic body forms called polyp and medusa (Figure 4.6). The former
is a sessile and cylindrical form like Hydra, Adamsia, etc. whereas, the
Figure 4.7 latter is umbrella-shaped and free-swimming like Aurelia or jelly fish.
Diagrammatic view of Those cnidarians which exist in both forms exhibit alternation of
Cnidoblast generation (Metagenesis), i.e., polyps produce medusae asexually and
medusae form the polyps sexually (e.g., Obelia).
Examples: Physalia (Portuguese man-of-war), Adamsia (Sea anemone),
Pennatula (Sea-pen), Gorgonia (Sea-fan) and Meandrina (Brain coral).
ANIMAL KINGDOM
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15

4.2.3 Phylum – Ctenophora

Ctenophores, commonly known as sea walnuts or comb jellies
are exclusively marine, radially symmetrical, diploblastic
organisms with tissue level of organisation. The body bears
eight external rows of ciliated comb plates, which help in
locomotion (Figure 4.8). Digestion is both extracellular and
intracellular. Bioluminescence (the property of a living

d
organism to emit light) is well-marked in ctenophores. Sexes

e
are not separate. Reproduction takes place only by sexual
means. Fertilisation is external with indirect development.

h
Examples: Pleurobrachia and Ctenoplana.

T is
4.2.4 Phylum – Platyhelminthes

R l
They have dorso-ventrally flattened body, hence are called

b
flatworms (Figure 4.9). These are mostly endoparasites found

E
in animals including human beings. Flatworms are bilaterally

u
symmetrical, triploblastic and acoelomate animals with organ

C
level of organisation. Hooks and suckers are present in the Figure 4.8 Example of

p
parasitic forms. Some of them absorb nutrients from the host Ctenophora

N re
(Pleurobrachia)
directly through their body surface. Specialised cells called
flame cells help in osmoregulation and excretion. Sexes are not
separate. Fertilisation is internal and development is through

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many larval stages. Some members like Planaria possess high
regeneration capacity.

b
Examples: Taenia (Tapeworm), Fasciola (Liver fluke).

t o
o t
n
(a) (b)
Figure 4.9 Examples of Platyhelminthes : (a) Tape worm (b) Liver fluke
 52 BIOLOGY

4.2.5 Phylum – Aschelminthes

The body of the aschelminthes is circular in
cross-section, hence, the name roundworms
(Figure 4.10). They may be freeliving, aquatic
and terrestrial or parasitic in plants and animals.
Roundworms have organ-system level of body
organisation. They are bilaterally symmetrical,

d
triploblastic and pseudocoelomate animals.

e
Alimentary canal is complete with a well-
developed muscular pharynx. An excretory

h
tube removes body wastes from the body cavity

T s
through the excretory pore. Sexes are separate

i
(dioecious), i.e., males and females are distinct.

R l
Often females are longer than males. Fertilisation
is internal and development may be direct (the

E b
Male Female
young ones resemble the adult) or indirect.

u
Figure 4.10 Aschelminthes
Examples : Ascaris (Round Worm), Wuchereria

C
– Roundworm
(Filaria worm), Ancylostoma (Hookworm).

N re p 4.2.6 Phylum – Annelida

They may be aquatic (marine and fresh water) or

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terrestrial; free-living, and sometimes parasitic.
They exhibit organ-system level of body
organisation and bilateral symmetry. They are

b
triploblastic, metamerically segmented and
coelomate animals. Their body surface is

o
distinctly marked out into segments or

t
metameres and, hence, the phylum name
Annelida (Latin, annulus : little ring) (Figure 4.11).

t
They possess longitudinal and circular muscles
which help in locomotion. Aquatic annelids like

o
Nereis possess lateral appendages, parapodia,
which help in swimming. A closed circulatory

n
system is present. Nephridia (sing. nephridium)
help in osmoregulation and excretion. Neural
system consists of paired ganglia (sing. ganglion)
connected by lateral nerves to a double ventral
nerve cord. Nereis, an aquatic form, is dioecious,
but earthworms and leeches are monoecious.
Reproduction is sexual.

Figure 4.11 Examples of Annelida : (a) Nereis Examples : Nereis, Pheretima (Earthworm) and
(b) Hirudinaria Hirudinaria (Blood sucking leech).
ANIMAL KINGDOM
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35

4.2.7 Phylum – Arthropoda

This is the largest phylum of Animalia which
includes insects. Over two-thirds of all named
species on earth are arthropods (Figure 4.12).
They have organ-system level of organisation.
They are bilaterally symmetrical, triploblastic,
segmented and coelomate animals. The body

d
of arthropods is covered by chitinous (a) (b)
exoskeleton. The body consists of head, thorax

e
and abdomen. They have jointed appendages

h
(arthros-joint, poda-appendages). Respiratory
organs are gills, book gills, book lungs or

T s
tracheal system. Circulatory system is of open

i
type. Sensory organs like antennae, eyes

R l
(compound and simple), statocysts or balance

b
organs are present. Excretion takes place

E
through malpighian tubules. They are mostly

u
dioecious. Fertilisation is usually internal.

C
They are mostly oviparous. Development may (c) (d)

p
be direct or indirect.

N re
Examples: Economically important insects – Figure 4.12 Examples of Arthropoda :
Apis (Honey bee), Bombyx (Silkworm), Laccifer (a) Locust (b) Butterfly
(Lac insect) (c) Scorpion (d) Prawn

© e
Vectors – Anopheles, Culex and Aedes
(Mosquitoes)
Gregarious pest – Locusta (Locust)

b
Living fossil – Limulus (King crab).

4.2.8 Phylum – Mollusca

t o
This is the second largest animal phylum
(Figure 4.13). Molluscs are terrestrial or

t
aquatic (marine or fresh water) having an
organ-system level of organisation. They are

o
bilaterally symmetrical, triploblastic and
coelomate animals. Body is covered by a (a)

n
calcareous shell and is unsegmented with a
distinct head, muscular foot and visceral
hump. A soft and spongy layer of skin forms a
mantle over the visceral hump. The space
between the hump and the mantle is called the
mantle cavity in which feather like gills are
present. They have respiratory and excretory
functions. The anterior head region has sensory (b)
tentacles. The mouth contains a file-like Figure 4.13 Examples of Mollusca :
rasping organ for feeding, called radula. (a) Pila (b) Octopus
54 BIOLOGY

They are usually dioecious and oviparous with indirect

development.
Examples: Pila (Apple snail), Pinctada (Pearl oyster), Sepia
(Cuttlefish), Loligo (Squid), Octopus (Devil fish), Aplysia (Sea-
hare), Dentalium (Tusk shell) and Chaetopleura (Chiton).

4.2.9 Phylum – Echinodermata

d
(a)
These animals have an endoskeleton of calcareous ossicles

e
and, hence, the name Echinodermata (Spiny bodied, Figure
4.14). All are marine with organ-system level of organisation.

h
The adult echinoderms are radially symmetrical but larvae

T s
are bilaterally symmetrical. They are triploblastic and

i
coelomate animals. Digestive system is complete with mouth

R l
on the lower (ventral) side and anus on the upper (dorsal)
(b) side. The most distinctive feature of echinoderms is the

E b
presence of water vascular system which helps in
locomotion, capture and transport of food and respiration.

u
Figure 4.14 Examples of

C
Echinodermata : An excretory system is absent. Sexes are separate.

p
(a) Asterias Reproduction is sexual. Fertilisation is usually external.
(b) Ophiura

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Development is indirect with free-swimming larva.
Examples: Asterias (Star fish), Echinus (Sea urchin), Antedon
(Sea lily), Cucumaria (Sea cucumber) and Ophiura (Brittle

© e
star).

4.2.10 Phylum – Hemichordata

b
Hemichordata was earlier considered as a sub-phylum under
phylum Chordata. But now it is placed as a separate phylum

o
under non-chordata.

t
This phylum consists of a small group of worm-like
marine animals with organ-system level of organisation. They

t
are bilaterally symmetrical, triploblastic and coelomate

o
animals. The body is cylindrical and is composed of an
anterior proboscis, a collar and a long trunk (Figure 4.15).

n
Circulatory system is of open type. Respiration takes place
through gills. Excretory organ is proboscis gland. Sexes are
separate. Fertilisation is external. Development is indirect.
Examples: Balanoglossus and Saccoglossus.

4.2.11 Phylum – Chordata

Animals belonging to phylum Chordata are fundamentally
Figure 4.15 Balanoglossus characterised by the presence of a notochord, a dorsal
ANIMAL KINGDOM
ANIMAL KINGDOM 55
55

hollow nerve cord and paired pharyngeal Nerve cord Notochord

gill slits (Figure 4.16). These are bilaterally
symmetrical, triploblastic, coelomate with
organ-system level of organisation. They
possess a post anal tail and a closed circulatory
system. Post-anal part
Table 4.1 presents a comparison of salient
Gill slits

d
features of chordates and non-chordates.
Figure 4.16 Chordata characteristics

e
TABLE 4.1 Comparison of Chordates and Non-chordates

h
S.No. Chordates Non-chordates

T s
1. Notochord present. Notochord absent.

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2. Central nervous system is dorsal, Central nervous system is ventral, solid
hollow and single. and double.

E b
3. Pharynx perforated by gill slits. Gill slits are absent.

u
4. Heart is ventral. Heart is dorsal (if present).

C
5. A post-anal part (tail) is present. Post-anal tail is absent.

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Phylum Chordata is divided into three
subphyla: Urochordata or Tunicata,
Cephalochordata and Vertebrata.

© e
Subphyla Urochordata and
Cephalochordata are often referred to as

b
protochordates (Figure 4.17) and are
exclusively marine. In Urochordata, notochord
is present only in larval tail, while in

o
Cephalochordata, it extends from head to tail

t
region and is persistent throughout their life.

t
Examples: Urochordata – Ascidia, Salpa,
Doliolum; Cephalochordata – Branchiostoma

o
(Amphioxus or Lancelet).
The members of subphylum Vertebrata

n
possess notochord during the embryonic
period. The notochord is replaced by a
cartilaginous or bony vertebral column in the
adult. Thus all vertebrates are chordates but
all chordates are not vertebrates. Besides the Figure 4.17 Ascidia
basic chordate characters, vertebrates have a
ventral muscular heart with two, three or four
chambers, kidneys for excretion and
osmoregulation and paired appendages which
may be fins or limbs.
 56 BIOLOGY

The subphylum Vertebrata is further divided as follows:

Vertebrata
Division

Agnatha Gnathostomata
(lacks jaw) (bears jaw)

d
Super Class

e
Pisces Tetrapoda
(bear limbs)

h
(bear fins)
Class Class

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Class
1. Cyclostomata 1. Amphibia

i
1. Chondrichthyes
2. Reptilia

l
2. Osteichthyes

R
3. Aves
4. Mammals

E u b 4.2.11.1 Class – Cyclostomata

C p
All living members of the class Cyclostomata are
ectoparasites on some fishes. They have an

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elongated body bearing 6-15 pairs of gill slits
for respiration. Cyclostomes have a sucking and
circular mouth without jaws (Fig. 4.18). Their

© e
body is devoid of scales and paired fins.
Cranium and vertebral column are

b
cartilaginous. Circulation is of closed type.
Figure 4.18 A jawless vertebrate - Petromyzon Cyclostomes are marine but migrate for
spawning to fresh water. After spawning, within

o
a few days, they die. Their larvae, after

t
metamorphosis, return to the ocean.
Examples: Petromyzon (Lamprey) and Myxine

t
(Hagfish).

o
4.2.11.2 Class – Chondrichthyes

n
They are marine animals with streamlined body
(a)
and have cartilaginous endoskeleton
(Figure 4.19). Mouth is located ventrally.
Notochord is persistent throughout life. Gill
slits are separate and without operculum (gill
cover). The skin is tough, containing minute
placoid scales. Teeth are modified placoid
(b) scales which are backwardly directed. Their
jaws are very powerful. These animals are
Figure 4.19 Example of Cartilaginous fishes : predaceous. Due to the absence of air bladder,
(a) Scoliodon (b) Pristis they have to swim constantly to avoid sinking.
ANIMAL KINGDOM
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75

Heart is two-chambered (one auricle and one ventricle).

Some of them have electric organs (e.g., Torpedo) and
some possess poison sting (e.g., Trygon). They are
cold-blooded (poikilothermous) animals, i.e., they lack
the capacity to regulate their body temperature. Sexes
are separate. In males pelvic fins bear claspers. They
have internal fertilisation and many of them are
viviparous.

d
Examples: Scoliodon (Dog fish), Pristis (Saw fish),

e
Carcharodon (Great white shark), Trygon (Sting ray).

h
4.2.11.3 Class – Osteichthyes

T s
It includes both marine and fresh water fishes with bony

i
endoskeleton. Their body is streamlined. Mouth is

R l
mostly terminal (Figure 4.20). They have four pairs of
gills which are covered by an operculum on each side.

E b
Skin is covered with cycloid/ctenoid scales. Air bladder

u
is present which regulates buoyancy. Heart is two-
(a) (b)

C
chambered (one auricle and one ventricle). They are

p
cold-blooded animals. Sexes are separate. Fertilisation Figure 4.20 Examples of Bony fishes :

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is usually external. They are mostly oviparous and (a) Hippocampus (b) Catla
development is direct.
Examples: Marine – Exocoetus (Flying fish),

© e
Hippocampus (Sea horse); Freshwater – Labeo (Rohu),
Catla (Katla), Clarias (Magur); Aquarium – Betta

b
(Fighting fish), Pterophyllum (Angel fish).

4.2.11.4 Class – Amphibia

o
As the name indicates (Gr., Amphi : dual, bios, life),

t
amphibians can live in aquatic as well as terrestrial
(a)
habitats (Figure 4.21). Most of them have two pairs of

t
limbs. Body is divisible into head and trunk. Tail may
be present in some. The amphibian skin is moist

o
(without scales). The eyes have eyelids. A tympanum

n
represents the ear. Alimentary canal, urinary and
reproductive tracts open into a common chamber called
cloaca which opens to the exterior. Respiration is by
gills, lungs and through skin. The heart is three-
chambered (two auricles and one ventricle). These are
cold-blooded animals. Sexes are separate. Fertilisation
(b)
is external. They are oviparous and development
is indirect.
Figure 4.21 Examples of Amphibia :
Examples: Bufo (Toad), Rana (Frog), Hyla (Tree frog),
(a) Salamandra
Salamandra (Salamander), Ichthyophis (Limbless (b) Rana
amphibia).
58 BIOLOGY

e d
T s h
i
(a) (b) (c) (d)

R l
Figure 4.22 Reptiles : (a) Chameleon (b) Crocodilus (c) Chelone (d) Naja

E b
4.2.11.5 Class – Reptilia

C u
The class name refers to their creeping or crawling mode of locomotion

p
(Latin, repere or reptum, to creep or crawl). They are mostly terrestrial

N re
animals and their body is covered by dry and cornified skin, epidermal
scales or scutes (Fig. 4.22). They do not have external ear openings.
Tympanum represents ear. Limbs, when present, are two pairs. Heart is

© e
usually three-chambered, but four-chambered in crocodiles. Reptiles are
poikilotherms. Snakes and lizards shed their scales as skin cast. Sexes
are separate. Fertilisation is internal. They are oviparous and development

b
is direct.
Examples: Chelone (Turtle), Testudo (Tortoise), Chameleon (Tree lizard),

o
Calotes (Garden lizard), Crocodilus (Crocodile), Alligator (Alligator).

t
Hemidactylus (Wall lizard), Poisonous snakes – Naja (Cobra), Bangarus

t
(Krait), Vipera (Viper).

o
4.2.11.6 Class – Aves
The characteristic features of Aves (birds) are the presence of feathers

n
and most of them can fly except flightless birds (e.g., Ostrich). They possess
beak (Figure 4.23). The forelimbs are modified into wings. The hind limbs
generally have scales and are modified for walking, swimming or clasping
the tree branches. Skin is dry without glands except the oil gland at the
base of the tail. Endoskeleton is fully ossified (bony) and the long bones
are hollow with air cavities (pneumatic). The digestive tract of birds has
additional chambers, the crop and gizzard. Heart is completely four-
chambered. They are warm-blooded (homoiothermous) animals, i.e.,
they are able to maintain a constant body temperature. Respiration is by
ANIMAL KINGDOM
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95

e d
(a) (b)

T s h (c) (d)

R li
Figure 4.23 Some birds : (a) Neophron (b) Struthio (c) Psittacula (d) Pavo

E b
lungs. Air sacs connected to lungs supplement respiration. Sexes are

u
separate. Fertilisation is internal. They are oviparous and development is

C
direct.

N re p
Examples : Corvus (Crow), Columba (Pigeon), Psittacula (Parrot), Struthio
(Ostrich), Pavo (Peacock), Aptenodytes (Penguin), Neophron (Vulture).

© e
4.2.11.7 Class – Mammalia
They are found in a variety of habitats – polar ice caps, deserts, mountains,
forests, grasslands and dark caves. Some of them have adapted to fly or

b
live in water. The most unique mammalian characteristic is the presence
of milk producing glands (mammary glands) by which the young ones

o
are nourished. They have two pairs of limbs, adapted for walking, running,
climbing, burrowing, swimming or flying (Figure 4.24). The skin of

t t
no (a)
(c)

(d)
(b)
Figure 4.24 Some mammals : (a) Ornithorhynchus (b) Macropus (c) Pteropus (d) Balaenoptera
 60 BIOLOGY

mammals is unique in possessing hair. External ears or pinnae are

present. Different types of teeth are present in the jaw. Heart is four-
chambered. They are homoiothermous. Respiration is by lungs. Sexes
are separate and fertilisation is internal. They are viviparous with few
exceptions and development is direct.
Examples: Oviparous-Ornithorhynchus (Platypus); Viviparous -
Macropus (Kangaroo), Pteropus (Flying fox), Camelus (Camel), Macaca
(Monkey), Rattus (Rat), Canis (Dog), Felis (Cat), Elephas (Elephant),

d
Equus (Horse), Delphinus (Common dolphin), Balaenoptera (Blue whale),

e
Panthera tigris (Tiger), Panthera leo (Lion).
The salient distinguishing features of all phyla under animal kingdom

h
is comprehensively given in the Table 4.2.

T s
TABLE 4.2 Salient Features of Different Phyla in the Animal Kingdom

R li
Phylum Level of Symme- Coelom Segmen- Digestive Circu- Respi- Distinctive
Organi- try tation System latory ratory Features

b
sation System System

Porifera Cellular

C E
Various

u
Absent Absent Absent Absent Absent Body with pores
and canals in walls.

p
Coelenterata

N re
Cnidoblasts
(Cnidaria) Tissue Radial Absent Absent Incomplete Absent Absent present.

Tissue Radial Absent Absent Incomplete Absent Absent Comb plates for
Ctenophora

© e
locomotion.
Organ &
Platyhelm- Organ- Bilateral Absent Absent Incomplete Absent Absent Flat body, suckers.
inthes system

b
Organ- Pseudo Often worm-
Aschelmin- Bilateral coelo- Absent Complete Absent Absent shaped,
system
thes mate elongated.

o
Organ- Coelo- Body segment-

t
Annelida system Bilateral mate Present Complete Present Absent ation like rings.
Organ- Exoskeleton of cu-
Bilateral Coelo-

t
Present Complete Present Present
ticle, jointed ap-
Arthropoda system mate
pendages.

o
Organ- Bilateral Coelo- Absent Complete Present Present External skeleton
Mollusca system mate of shell usually

n
present.

Organ- Water vascular

Echino- Radial Coelo- Absent Complete Present Present
system system, radial
dermata mate
symmetry.
Organ- Bilateral Coelo- Wor m-like with
Hemi- Absent Complete Present Present
system mate proboscis, collar
chordata
and trunk.
Notochord, dorsal
Chordata Organ- Bilateral Coelo- Present Complete Present Present hollow nerve cord,
system mate gill slits with
limbs or fins.
ANIMAL KINGDOM
ANIMAL KINGDOM 61
16

SUMMARY

The basic fundamental features such as level of organisation, symmetry, cell

organisation, coelom, segmentation, notochord, etc., have enabled us to broadly
classify the animal kingdom. Besides the fundamental features, there are many
other distinctive characters which are specific for each phyla or class.

d
Porifera includes multicellular animals which exhibit cellular level of
organisation and have characteristic flagellated choanocytes. The coelenterates

e
have tentacles and bear cnidoblasts. They are mostly aquatic, sessile or free-floating.

h
The ctenophores are marine animals with comb plates. The platyhelminths have
flat body and exhibit bilateral symmetry. The parasitic forms show distinct suckers

T is
and hooks. Aschelminthes are pseudocoelomates and include parasitic as well as

l
non-parasitic round worms.

R
Annelids are metamerically segmented animals with a true coelom. The

E b
arthropods are the most abundant group of animals characterised by the presence
of jointed appendages. The molluscs have a soft body surrounded by an external

C u
calcareous shell. The body is covered with external skeleton made of chitin. The

p
echinoderms possess a spiny skin. Their most distinctive feature is the presence

N re
of water vascular system. The hemichordates are a small group of worm-like marine
animals. They have a cylindrical body with proboscis, collar and trunk.
Phylum Chordata includes animals which possess a notochord either

© e
throughout or during early embryonic life. Other common features observed in
the chordates are the dorsal, hollow nerve cord and paired pharyngeal gill slits.

b
Some of the vertebrates do not possess jaws (Agnatha) whereas most of them possess
jaws (Gnathostomata). Agnatha is represented by the class, Cyclostomata. They
are the most primitive chordates and are ectoparasites on fishes. Gnathostomata

o
has two super classes, Pisces and Tetrapoda. Classes Chondrichthyes and

t
Osteichthyes bear fins for locomotion and are grouped under Pisces. The
Chondrichthyes are fishes with cartilaginous endoskeleton and are marine. Classes,

t
Amphibia, Reptilia, Aves and Mammalia have two pairs of limbs and are thus

o
grouped under Tetrapoda. The amphibians have adapted to live both on land and
water. Reptiles are characterised by the presence of dry and cornified skin. Limbs

n
are absent in snakes. Fishes, amphibians and reptiles are poikilothermous (cold-
blooded). Aves are warm-blooded animals with feathers on their bodies and
forelimbs modified into wings for flying. Hind limbs are adapted for walking,
swimming, perching or clasping. The unique features of mammals are the presence
of mammary glands and hairs on the skin. They commonly exhibit viviparity.
62 BIOLOGY

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?

d
3. How useful is the study of the nature of body cavity and coelom in the

e
classification of animals?
4. Distinguish between intracellular and extracellular digestion?

h
5. What is the difference between direct and indirect development?

T is
6. What are the peculiar features that you find in parasitic platyhelminthes?

R l
7. What are the reasons that you can think of for the arthropods to constitute the

b
largest group of the animal kingdom?

E
8. Water vascular system is the characteristic of which group of the following:

u
(a) Porifera (b) Ctenophora (c) Echinodermata (d) Chordata

C p
9. “All vertebrates are chordates but all chordates are not vertebrates”. Justify the

N re
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?

© e
12. Could the number of eggs or young ones produced by an oviparous and viviparous
mother be equal? Why?

b
13. Segmentation in the body is first observed in which of the following:
(a) Platyhelminthes (b) Aschelminthes (c) Annelida (d) Arthropoda

t o
14. Match the following:
(a) Operculum (i) Ctenophora

t
(b) Parapodia (ii) Mollusca

o
(c) Scales (iii) Porifera
(d) Comb plates (iv) Reptilia

n
(e) Radula (v) Annelida
(f ) Hairs (vi) Cyclostomata and Chondrichthyes
(g) Choanocytes (vii) Mammalia
(h) Gill slits (viii) Osteichthyes
15. Prepare a list of some animals that are found parasitic on human beings.