Chapter 4
ANIMAL KINGDOM
(Syllabus: Salient features and classification of animals, non-chordates up to phyla level and chordates up to class level (salient features and a few examples of each category). (No live animals or specimen should be displayed.)
A. BASIS OF CLASSIFICATION
1. Arrangement of cells/ Level of
organizations.
2. Body symmetry.
3. Diploblastic and Triploblastic
Organisation
4. Nature of coelom.
5. Segmentation
6. Notochord
7. Patterns of digestive, circulatory or reproductive systems.
A/1. Arrangement of cells/ Level of
organizations
1. Though all members of Animalia are
multicellular, all of them do not exhibit the same pattern of organisation of
cells.
Level of organizations is
of three types:
1. Cellular level of organisation
2. Tissue level of organization
3. Organ system level of organization
1. Cellular level of organization
In sponges,
the cells are arranged as loose cell aggregates, i.e., they exhibit cellular
level of organization.
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2. Tissue level of
organization
1. In coelenterates, the arrangement
of cells is more complex.
2. Here the cells performing the same
function are arranged into tissues, hence is called tissue level of
organisation.
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3. Organ system level of organization
1. 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. This pattern is called organ system level
of organisation.
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3. Organ systems in different groups
of animals exhibit various patterns of complexities.
For example
i) Incomplete
digestive system: The digestive system in Platyhelminthes has only a
single opening to the outside of the body that serves as both mouth and anus,
and is hence called incomplete.
ii) Complete digestive
system : A complete
digestive system has two openings, mouth and anus.
Similarly, the circulatory system may
be of two types:
(i) Open type:
Open type in which the blood is pumped
out of the heart and the cells and tissues are directly bathed in it.
(ii) Closed
type : Closed type in which the blood is circulated through a series of
vessels of varying diameters (arteries, veins and capillaries).
A/2. Symmetry
1. Animals can be categorised on the
basis of their symmetry as
i) Symmetrical ii)
Asymmetrical
i) Symmetrical: It can be further divided into two categories:
a) Bilateral symmetry b) Radial
symmetry
a) Bilateral symmetry: Animals like annelids, arthropods,
etc., where the body can be divided into identical left and right halves in
only one plane, exhibit bilateral symmetry.
b) Radial symmetry: When
any plane passing
through the central axis of the body divides the organism into two identical
halves, it is called radial symmetry. Coelenterates, ctenophores and
echinoderms have this kind of body plan.
ii) Asymmetrical: Sponges (porifera) are mostly
asymmetrical, i.e., any plane that passes through the centre does not divide
them into equal halves.
A/3. Diploblastic and
Triploblastic Organisation
During the embryonic development some
layers are formed called as embryonic layers or germ layers .
The layers may be two or three : i) Ectoderm ii) Endoderm iii) Mesoderm
Examples of
i)
Ectoderm :
Skin
and hair, Nervous system
ii) Endoderm : Internal soft organs like Stomach,
intestines, liver, pancreas
iii) Mesoderm: Vital organs like heart, blood
vessels, kidneys etc.
On the basis of these layers animals
by of two types:
i) Diploblastic ii)
Triploblastic
i) Diploblastic : Animals in which the cells are arranged in two embryonic
layers, an external ectoderm and an internal endoderm, are called diploblastic
animals, e.g., coelenterates.
In such animals as the third layer is
absent so an undifferentiated layer, mesoglea,
is present in between the ectoderm and the endoderm to perform the function of
mesoderm.
ii) Triploblastic : 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.
A/4 Nature of Coelom
1. Presence
or absence of a cavity between the body wall and the gut wall is very
important in classification.
Depending upon the cavity lined by
mesoderm or not, animals can be divided into three categories:
i) Coelomates ii)
Pseudocoelomates iii)
Acoelomates
i) Coelomates : The body cavity, which is lined by
mesoderm is called coelom. Animals possessing coelom are called coelomates.
ii) Pseudocoelomates: 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.
iii) Acoelomates: The animals in which the body cavity
is absent are called acoelomates, e.g., platyhelminthes.
A/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.
A/6 Notochord
1.
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.
2.
Its primary function is to
provide rigidity and support to the body.
B. CLASSIFICATION OF
ANIMALS
B/1 Phylum – Porifera
1. Members of this phylum are
commonly known as sponges.
Habitat
1. They are generally marine and
mostly asymmetrical animals.
Structure
1. These are primitive multicellular
animals and have cellular
level of organisation.
2. Sponges have a water transport or canal system.
3. Water enters through minute pores (ostia) in the body wall into a
central cavity, spongocoel, from where it goes out through the osculum.
4. This pathway of water transport is
helpful in food gathering, respiratory exchange and removal of waste.
5. Choanocytes or collar cells
are primarily responsible for capturing food particles from the
water. The beating motion of the flagellum creates water currents that draw in
food particles. The collar acts as a sieve, trapping and engulfing food
particles such as bacteria, plankton, and organic debris. Choanocytes
line the spongocoel and
the canals.
6. Digestion is intracellular (inside the
cell).
7. The body is supported by a
skeleton made up of spicules
(Spicules provide structural support to
the sponge's body) or spongin fibres.
Reproduction
i) Asexual reproduction ii) Sexual
reproduction
i) Asexual reproduction
1. Sponges reproduce asexually by
fragmentation.
ii) Sexual reproduction
1. Sexes are not separate (hermaphrodite),
i.e., eggs and sperms are produced by the same individual.
2.
Reproduction takes place by formation of gametes.
3. Fertilisation is internal and
development is indirect having a larval stage which is morphologically distinct from
the adult.
4. Examples: Sycon (Scypha), Spongilla (Fresh water sponge) and Euspongia
(Bath sponge).
B/ 2 Phylum – Coelenterata (Cnidaria) (due to the presence of central cavity which
is known as coelenteron and known as cnidaria due to the presence of stinging cells
termed as cnidobast)
Habitat
1. They are aquatic, mostly marine,
sessile or free-swimming, radially symmetrical animals.
Structure
1.
The name cnidaria is derived from the cnidoblasts
or cnidocytes
(which contain the stinging capsules or nematocysts) present on the tentacles and
the body.
2. Cnidoblasts are used for anchorage, defense
and for the capture of prey.
3. Cnidarians exhibit tissue level of organisation
and are diploblastic.
4. They have a central gastro-vascular cavity
with a single opening, mouth on hypostome (The hypostome is surrounded by a ring
of tentacles, which are armed with stinging cells called nematocysts.
) The
gastro-vascular cavity is a central body cavity that serves both digestive and circulatory
functions.
5. Digestion is extracellular (inside the gastrovascular cavity with the help of
digestive juices) and intracellular (
in the food vacuole). Firstly food is
digested in the extracellular cavity and then the digested food transferred to
food vacuole for further digestion termed as intracellular.
6. Some of the cnidarians, e.g.,
corals have a skeleton composed of calcium carbonate.
7. Cnidarians exhibit two basic body
forms called polyp and medusa.
Polyp:
1. It is a sessile (non motile) and cylindrical form
like Hydra, Adamsia, etc.
Medusa: It is umbrella-shaped and
free-swimming like Aurelia or jelly fish.
Reproduction
1. Those cnidarians which exist in
both forms exhibit alternation of generation
(Metagenesis, between sexual and asexual forms), i.e., polyps produce medusae
asexually and medusae form the polyps sexually (e.g., Obelia).
2. Hydra reproduce asexually with the
process called budding.
2. Examples: Physalia (Portuguese
man-of-war), Adamsia (Sea anemone), Pennatula (Sea-pen), Gorgonia (Sea-fan) and
Meandrina (Brain coral).
The name
"Ctenophora" is derived from Greek roots. "Cteno-" comes
from the Greek word "ktenos," meaning "comb," and "phora"
is derived from "phoreus," which means "bearer" or
"carrier."
Habitat
1. Ctenophores, commonly known as sea
walnuts or comb jellies are exclusively marine.
Structure
1. Radially
symmetrical, diploblastic organisms with tissue level of organisation.
2. The
body bears eight external rows of ciliated comb plates, which help in
locomotion.
3. Digestion is both extracellular
and intracellular.
4. Bioluminescence
(the property of a living organism to emit light) is well-marked in
ctenophores.
Reproduction
1. Sexes are not separate.
2. Reproduction takes place only by
sexual means.
3. Fertilisation is external with indirect
development (formation of larva).
4. Examples: Pleurobrachia and
Ctenoplana.
B/4. Phylum –
Platyhelminthes (Platy
means Flat and helminthes means worm)
1. They have dorso-ventrally
flattened body, hence are called flatworms.
2. Flatworms are bilaterally symmetrical, triploblastic
and acoelomate animals with organ level of organisation.
Nutrition
1. These are mostly endoparasites found in animals including human beings.
2. Hooks and suckers are present in
the parasitic forms.
3. Some of them absorb nutrients from
the host directly through their body surface.
Excretion
i.
Specialised cells called flame cells (Flame cells
function like a kidney and removes waste materials. Bundles of flame cells are
called protonephridia) help in osmoregulation and excretion.
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Osmoregulation is the way living things control the balance of
water and salts in their bodies |
Reproduction
1. Sexes are not separate.
2. Fertilisation is internal and billions of eggs fertilized
at a time and development is through many larval stages.
3. Some members like Planaria possess
high regeneration capacity. For example if it is cut into two pieces then both
of them regenerate to full individual. It is also reproduce asexually.
4. Examples: Taenia (Tapeworm),
Fasciola (Liver fluke).
Planaria regeneration video: https://www.youtube.com/watch?v=hTC1eNTBXvE
B/5 Phylum – Aschelminthes ( round worms)
Habitat and Nutrition
1. They may be free living, aquatic
and terrestrial or parasitic in plants and animals.
Structure
1. The body of the aschelminthes is
circular in cross-section, hence, the name roundworms.
2. Roundworms have organ-system level of body organisation.
3. They are bilaterally
symmetrical, triploblastic and pseudocoelomate animals.
Digestion
1. Alimentary canal is complete with
a well developed muscular pharynx (It is located in the throat region
and connects the mouth to the digestive system).
Excretion
1. An excretory
tube removes body wastes from the body cavity through the excretory pore.
Reproduction
1. Sexes are separate
(dioecious), i.e., males and females are distinct.
2. Often females are longer than
males.
3. Fertilisation is internal and development
may be direct or indirect.
4. Examples : Ascaris (Roundworm),
Wuchereria (Filaria worm), Ancylostoma (Hookworm).
Habitat
1. They may be aquatic (marine and
fresh water) or terrestrial; free-living, and sometimes parasitic.
Structure
1. They exhibit organ-system level of
body organisation and bilateral symmetry.
2. They are triploblastic,
metamerically segmented (each segment possess similar kind of muscles and
organs) and coelomate animals.
3. Their body surface is distinctly
marked out into segments or metameres and, hence, the phylum name Annelida
(Latin, annulus : little ring).
4. They possess longitudinal and
circular muscles which help in locomotion.
5. Aquatic annelids like Nereis
possess lateral appendages, parapodia, which help in swimming.
Organs
Blood circulatory system
1. A closed
circulatory system is present.
2. Heart is present.
Excretion
1. Nephridia
(sing. nephridium) help in osmoregulation (Osmoregulation is the biological process by which
organisms regulate the balance of water and solutes (such as salts and ions)
within their bodies to maintain a stable internal environment, despite changes
in external conditions) and excretion.
Respiration
1. Through skin.
Nervous system
1. Neural system consists of paired
ganglia (sing. Ganglion, ganglia refers to clusters of nerve cell bodies) connected by
lateral nerves to a double ventral nerve cord.
Reproduction
1. Nereis, an aquatic form, is dioecious, but earthworms and leeches are
monoecious.
2. Reproduction is sexual.
3. Examples : Nereis, Pheretima
(Earthworm) and Hirudinaria (Blood sucking leech).
B/7 Phylum – Arthropoda (arthros-joint, poda-appendages)
1. This is the largest phylum of Animalia which includes insects.
2. Over two-thirds of all named
species on earth are arthropods.
Structure
1. They have organ-system level of
organisation.
2. They are bilaterally symmetrical,
triploblastic, segmented and coelomate animals.
3. The body of arthropods is covered
by chitinous exoskeleton (Chitin is a complex carbohydrate.)
4. The body consists of head, thorax
and abdomen.
5. They have jointed appendages
(arthros-joint, poda-appendages).
Organs
1. Respiratory
organs are gills, book gills, book
lungs or tracheal system.
2. Circulatory
system is of open type.
3. Sensory
organs like antennae (They can perceive a
wide range of sensory information, including touch, vibration, temperature,
humidity, chemical signals (smell and taste), and even sounds or airborne
vibrations.), eyes
(compound and simple), statocysts
or balancing organs are present (The
statocyst is a sensory organ found in some arthropods, particularly in
crustaceans and some insects. Its primary role is to sense gravity and provide
information about the animal's orientation and equilibrium).
4. Excretion takes place through malpighian tubules (Terrestrial
arthropods have malpighian tubules, which collect waste from
the blood and add it to undigested food to be excreted).
Reproduction
1. They are mostly dioecious.
2. Fertilisation is usually internal.
3. They are mostly oviparous.
4. Development may be direct or
indirect.
5. Examples: Economically important
insects – Apis (Honey bee), Bombyx (Silkworm), Laccifer (Lac insect) Vectors –
Anopheles, Culex and Aedes (Mosquitoes) Gregarious (Living
in colonies but don’t depend on one another) pest – Locusta (Locust)
Living fossil – Limulus (King crab).
B/8. Phylum – Mollusca
This
is the second largest animal phylum.
Habitat
1. Molluscs are terrestrial or
aquatic (marine or fresh water) having an organ-system level of organisation.
2. They are bilaterally symmetrical,
triploblastic and coelomate animals.
3. Body is covered by a calcareous
shell and is unsegmented with a distinct head, muscular foot and visceral
(soft) hump. This hump has some soft organs inside.
4. A soft and spongy layer of skin
forms a mantle over the visceral hump.
5. The space between the hump and the
mantle is called the mantle cavity in which feather like gills are present.
6.
They have respiratory and excretory functions.
7.
The anterior head region has sensory tentacles.
8.
The mouth contains a file-like (a tool used to smooth or shape material) rasping organ for feeding, called radula.
4. They are usually dioecious and
oviparous with indirect development.
5. Examples: Pila (Apple snail), Pinctada (Pearl oyster), Sepia
(Cuttlefish), Loligo (Squid), Octopus (Devil fish), Aplysia (Seahare),
Dentalium (Tusk shell) and Chaetopleura (Chiton).
B/9. Phylum – Echinodermata
(Spiny skin)
Structure
1. These animals have an endoskeleton of calcareous
ossicles (small calcareous elements which are embedded in the dermis of
the body wall ) and, hence, the name
Echinodermata (Spiny bodied).
2. All are marine with organ-system
level of organisation.
3. The adult echinoderms are radially
symmetrical but larvae are bilaterally symmetrical.
4. They are triploblastic and
coelomate animals.
Organ
1. Digestive system is complete with
mouth on the lower (ventral) side and anus on the upper (dorsal) side.
ii.
The most distinctive feature of echinoderms is the
presence of water vascular system which helps in locomotion, capture and
transport of food and respiration.
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The madreporite allows seawater to enter the water vascular
system |
3. An
excretory system is absent.
Reproduction
1. Sexes are separate.
2. Reproduction is sexual.
3. Fertilization is usually external.
4. Development is indirect with
free-swimming larva.
5. Examples: Asterias (Star fish), Echinus (Sea urchin), Antedon (Sea
lily), Cucumaria (Sea cucumber) and Ophiura (Brittle star).
General Characteristics
1. Hemichordata was earlier considered as a sub-phylum under
phylum Chordata. But now it is placed as a separate phylum under non-chordata.
2. Hemichordates have a rudimentary
structure in the collar region called stomochord, a structure similar to
notochord.
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Notochord |
Stomochord |
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Location:
Located along the dorsal (back) side of the embryo, running the length of the
body. Structure: A flexible, rod-like structure composed of a core of
large, vacuolated cells surrounded by a firm sheath of connective tissue. It
is more rigid and supportive than the stomochord. Origin: Develops from the mesoderm (the middle layer of
cells in the early embryo). |
Location: Situated in the collar region, extending from the
dorsal side of the mouth into the proboscis. Structure: Tubular, rod-like, filled with vacuolated cells
and surrounded by a sheath. It is less rigid than the notochord. Origin: Develops from the endoderm (the innermost layer of
cells in the early embryo). |
3. This phylum consists of a small
group of worm-like marine animals with organ-system level of organisation.
Structure
1. They are bilaterally symmetrical,
triploblastic and coelomate animals.
2. The body is cylindrical and is
composed of an anterior proboscis (The proboscis is a muscular and ciliated organ
used in locomotion and in the
collection and transport of food particles), a collar and a long trunk.
Organ
1. Circulatory system is of open type.
2. Respiration takes place through gills.
3. Excretory
organ is proboscis gland. Blood from
the vascular system enters the proboscis gland, where waste products and excess
substances are filtered out.
Reproduction
1. Sexes are separate.
2. Fertilisation is external.
3. Development is indirect.
4. Examples: Balanoglossus and
Saccoglossus.
Comparison of salient features of
chordates and non-chordates.
General Characteristics
1. Animals belonging to phylum Chordata are fundamentally
characterised by the presence of a notochord, a dorsal hollow nerve cord and
paired pharyngeal gill slits (Pharyngeal gill slits, also known as pharyngeal slits or gill
slits, are openings in the pharynx (throat) region of various animals.) Water
is taken in through the mouth and passes over the gill slits, allowing for the
exchange of oxygen and carbon dioxide with the surrounding water. (Figure 4.16).
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Nerve
cord |
Notochord |
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1. The nerve cord is primarily composed of neurons or nerve cells. |
1. The notochord is a flexible, rod-like structure that plays a
crucial role in the development and function of chordates, a phylum that
includes all vertebrates (such as humans) and some invertebrates. |
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2. It is responsible for transmitting electrical signals or nerve
impulses throughout the body, facilitating communication between different
parts of the organism. |
2. Its primary function is to provide rigidity and support to the
body. 3. In vertebrates, the notochord is largely replaced by the vertebral
column (spine) as development progresses. |
Structure
1. These are bilaterally symmetrical,
triploblastic, coelomate with organ-system level of organisation.
2. They possess a post anal tail and
a closed circulatory system.
Classification
1. Phylum Chordata is divided into
three subphyla:
(a) Urochordata
or Tunicata, (b) Cephalochordata
and (c) Vertebrata.
2. Subphyla Urochordata and
Cephalochordata are often referred to as protochordates (Figure 4.17) and are
exclusively marine.
(a) Subphyla Urochordata
1. In Urochordata, notochord is present only in
larval tail.
(b) Subphyla
Cephalochordata
1. In Cephalochordata, it extends from head to tail region
and is persistent throughout their life. Examples: Urochordata – Ascidia,
Salpa, Doliolum; Cephalochordata – Branchiostoma (Amphioxus or Lancelet).
(c) Subphylum Vertebrata
1. The members of subphylum
Vertebrata possess notochord during the embryonic
period.
2. The notochord is replaced by a cartilaginous or bony
vertebral column in the adult.
3. Thus all vertebrates are chordates but all chordates are not
vertebrates.
Note :-
1. Notochord is a structure that
provides support to the nerve chord.
2. In vertebrates the notochord is
developed into vertebral column, so called vertebrates.
3. The spinal cord is a specific type of nerve cord found in
vertebrates and is located dorsally (back) within the vertebral column or
spinal column.
Organs
1. Besides the basic chordate
characters, vertebrates have a ventral muscular heart with two, three or four
chambers.
2. Kidneys for excretion and
osmoregulation.
3. Paired appendages which may be
fins or limbs.
B/11/1. Class –
Cyclostomata
1. All living members of the class
Cyclostomata are ectoparasites on some fishes.
Structure
1. They have an elongated body
bearing 6-15 pairs of gill slits for respiration.
2. Cyclostomes have a sucking and
circular mouth without jaws (Fig. 4.18).
3. Their body is devoid of scales and
paired fins.
4. Cranium
(The cranium, also known as the skull, is the bony structure that forms
the head of vertebrates, including humans) and vertebral column are cartilaginous.
Circulation
1. Circulation is of closed type.
Life cycle
1. Cyclostomes are marine but migrate
for spawning to fresh water.
2. After spawning, within a few days,
they die. Their larvae, after metamorphosis, return to the ocean.
3. Examples: Petromyzon (Lamprey) and
Myxine (Hagfish).
B/11/2. Class –
Chondrichthyes
1. They are marine animals with
streamlined body and have cartilaginous endoskeleton (Figure 4.19).
2. Mouth is located ventrally.
3. Notochord is persistent throughout
life.
4. Gill slits are separate and
without operculum (gill cover).
5. The skin is tough, containing
minute placoid scales
(These scales are hard and have a
pointed shape that helps in protection and movement. Over time, some of these
scales became specialized and developed into teeth, which are also hard and
pointed but adapted for biting and chewing food. So, teeth are like modified versions of these
backward-pointing scales.).
6. Teeth are modified placoid scales
which are backwardly directed.
7. Their jaws are very powerful.
8. These animals are predaceous.
9. Due to the absence of air bladder,
they have to swim constantly to avoid sinking.
10. Heart is two-chambered
(one auricle and one ventricle).
11. Some of them have electric organs (e.g., Torpedo) and some possess poison sting (e.g., Trygon).
Torpedo Trygon
12. They are cold-blooded
(poikilothermous) animals, i.e., they lack the capacity to regulate their body
temperature.
Reproduction
1. Sexes are separate.
2. In males pelvic fins bear
claspers.
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1. Pelvic
fins:
Pelvic fins are paired fins located on the ventral
(bottom) surface of fishes specifically in bony fishes
(Osteichthyes) and cartilaginous fishes (Chondrichthyes). They are positioned
in the region of the fish's abdomen near the pelvic girdle hence their name. 2. Claspers: During mating, the male fish uses the claspers to inseminate the
female. The claspers are inserted into the female's reproductive tract,
typically into her cloaca, which is the common opening for the reproductive,
urinary, and digestive tracts. |
3. They have internal fertilisation
and many of them are viviparous.
4. Examples: Scoliodon (Dog fish), Pristis (Saw fish), Carcharodon (Great
white shark), Trygon (Sting ray).
B/11/3. Class –
Osteichthyes
1. It includes both marine and fresh
water fishes with bony endoskeleton.
2. Their body is streamlined.
3. Mouth is mostly terminal (Figure
4.20).
4. They have four pairs of gills
which are covered by an operculum on each side.
5. Skin is covered with cycloid/ctenoid scales.
6. Air bladder is present which
regulates buoyancy.
7. Heart
is two chambered (one auricle and one
ventricle).
8. They are cold-blooded
animals.
Reproduction
1. Sexes are separate.
2. Fertilisation is usually external.
3. They are mostly oviparous and development is
direct.
4. Examples: Marine – Exocoetus (Flying fish), Hippocampus (Sea horse);
Freshwater – Labeo (Rohu), Catla (Katla), Clarias (Magur); Aquarium – Betta
(Fighting fish), Pterophyllum (Angel fish).
Habitat
1. As the name indicates (Gr., Amphi
: dual, bios, life), amphibians can live in aquatic as well as terrestrial
habitats (Figure 4.21).
Structure
1. Most of them have two pairs of
limbs.
2. Body is divisible into head and trunk.
3. Tail
may be present in some.
4. The amphibian skin is moist (without scales).
5. The eyes have eyelids.
6. A tympanum
represents the ear.
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The tympanum, also known as the eardrum, is an important auditory
structure found in frogs and many other amphibians. |
7. Alimentary canal, urinary and
reproductive tracts open into a common chamber called cloaca
which opens to the exterior.
8. Respiration is by gills, lungs and
through skin.
9. The heart
is three chambered (two auricles and one
ventricle).
10. These are cold-blooded animals.
Reproduction
1. Sexes are separate.
2. Fertilisation is external.
3. They are oviparous
and development is indirect.
4. Examples: Bufo (Toad), Rana (Frog), Hyla (Tree frog), Salamandra
(Salamander), Ichthyophis (Limbless amphibia).
B/11/5. Class – Reptilia
General Characteristics
& Habitat
1. The class name refers to their
creeping or crawling mode of locomotion (Latin, repere or reptum, to creep or
crawl).
2. They are mostly terrestrial
animals and their body is covered by dry and cornified skin, epidermal scales
or scutes (Fig. 4.22).
(i) Cornified skin refers to the outermost layer of
the epidermis that has undergone a process called cornification or
keratinization. This process involves the transformation of living skin cells
into tough, durable, and water-resistant cells. Cornified skin is commonly found
in terrestrial amphibians, such as frogs and toads, which require adaptations
to withstand the challenges of a terrestrial environment.
(ii) Scutes specifically refer to the specialized
scales found on certain parts of an amphibian's body. They are a characteristic
feature of some amphibians, contributing to their overall physical appearance
and providing defense against predators.
Structure
1. They do not have external ear
openings.
2. Tympanum
represents ear.
3. Limbs, when present, are two
pairs.
4. Heart is usually three-chambered, but
four-chambered in crocodiles.
5. Reptiles are poikilotherms (cold blooded).
6. Snakes and lizards shed their
scales as skin cast.
Reproduction
1. Sexes are separate.
2. Fertilisation is internal.
3. They are oviparous
and development is direct.
4. Examples: Chelone (Turtle), Testudo (Tortoise), Chameleon (Tree
lizard), Calotes (Garden lizard), Crocodilus (Crocodile), Alligator
(Alligator). Hemidactylus (Wall lizard), Poisonous snakes – Naja (Cobra),
Bangarus (Krait), Vipera (Viper).
B/11/6. Class – Aves
General Characteristics
1. The characteristic features of
Aves (birds) are the presence of feathers and most of them can fly except
flightless birds (e.g., Ostrich).
2. They possess beak (Figure 4.23).
3. The forelimbs are modified into
wings.
4. The hind
limbs generally have scales and are modified for
walking, swimming or clasping the tree branches.
5. Skin is dry without glands except
the oil gland at the base of the tail.
6. Endoskeleton is fully ossified
(bony) and the long bones are hollow with air cavities (pneumatic).
7. The digestive tract of birds has
additional chambers, the crop and gizzard.
|
i.
Crop: Its main function is to temporarily
store and soften food before it moves further along the digestive tract.
ii.
Grinding Action: Inside the gizzard, the strong muscles contract and relax,
grinding the food against the tough lining. Many birds also swallow small
stones or grit, which remain in the gizzard and help to grind the food into
smaller pieces, much like how teeth work in mammals. |
8. Heart
is completely four chambered.
9. They are warm-blooded
(homoiothermous “means same temperature)
animals, i.e., they are able to maintain a constant body temperature.
10. Respiration is by lungs.
11. Air sacs connected to lungs
supplement respiration.
Reproduction
1. Sexes are separate.
2. Fertilisation is internal.
3. They are oviparous
and development is direct.
4. Examples : Corvus (Crow), Columba (Pigeon), Psittacula (Parrot),
Struthio (Ostrich), Pavo (Peacock), Aptenodytes (Penguin), Neophron (Vulture).
General Characteristics
1. They are found in a variety of
habitats – polar ice caps, deserts, mountains, forests, grasslands and dark
caves.
2. Some of them have adapted to fly
or live in water.
3. The most unique mammalian
characteristic is the presence of milk producing glands
(mammary glands) by which the young ones are nourished.
4. They have two pairs of limbs,
adapted for walking, running, climbing, burrowing, swimming or flying (Figure
4.24).
5. The skin of mammals is unique in
possessing hair.
6. External ears or pinnae are
present.
7. Different types of teeth are
present in the jaw.
8. Heart
is four chambered.
9. They are homoiothermous.
10. Respiration is by lungs.
Reproduction
1. Sexes are separate and
fertilisation is internal.
2. They are viviparous with few
exceptions and development is direct.
3. Examples: Oviparous-Ornithorhynchus (Platypus); Viviparous - Macropus
(Kangaroo), Pteropus (Flying fox), Camelus (Camel), Macaca (Monkey), Rattus
(Rat), Canis (Dog), Felis (Cat), Elephas (Elephant), Equus (Horse), Delphinus
(Common dolphin), Balaenoptera (Blue whale), Panthera tigris (Tiger), Panthera
leo (Lion).
The salient distinguishing features
of all phyla under animal kingdom is comprehensively given table:
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