This document provides information on the classification of animals, describing their levels of organization, symmetry, embryonic layers, body cavities, and other characteristics used to group them into taxa. It discusses sponges, cnidarians, ctenophores, flatworms, roundworms, annelids, arthropods, molluscs, echinoderms, hemichordates, and chordates. Within chordates, it describes lampreys and hagfish, cartilaginous fishes, bony fishes, amphibians, and several classes of vertebrates. The classification system presented moves from simpler to more complex organisms and discusses key distinguishing features of each group.

1. RALLI INTERNATIONAL SCHOOL

3. Basis of Classification
Levels of organization
• Cellular level of organization: eg. in sponges ,cells are in loose
cell aggregates
• Tissue level of organization: eg. in coelenterates cells doing the
same function form tissues
• Organ level of organization: eg. Platyhelminths tissues are
organized to form organ specialized for a particular function
• Organ-System level of organization: eg. in Annelid ,
Arthropod , etc. Organ has associated to form functional system
with specific physiological function. Organ System show variations
from animal to animal eg. digestive system in platyhelminth has
only one opening but others has 2 openings mouth and anus.

4. Symmetry
Animals can be categorized 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. Coelenterates,
ctenophores and echinoderms have this
kind of body plan.
• Animals like annelids, arthropods, etc.,
where the body can be divided into
identical left and right halves in only
one plane, exhibit bilateral symmetry

5. Diploblastic and Triploblastic Organisation
Diploblastic animals: Animals in which the cells are arranged in
two embryonic layers, an external ectoderm and an internal
endoderm. e.g., coelenterates. An undifferentiated layer, mesoglea,
is present in between the ectoderm and the endoderm.
Triploblastic animals: Those animals in which the developing
embryo has a third germinal layer, mesoderm, in between the
ectoderm and endoderm. (platyhelminthes to chordates)

6. Coelom
Acoelomates :- NO
Coelom. eg. Platyhelminths
Pseudoceolomates :-
body cavity not lined by
mesoderm but mesoderm is
found in patches between
ectoderm & endoderm eg.
Aschelminths
Coelomate:- having true
Coelom. eg. annelids,
molluscs, arthropods,
echinoderms,
hemichordates and
chordates
The body cavity, which is lined by mesoderm

7. Segmentation: 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.
Notochord: 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.

8. Classification of Animals

9. Phylum – Porifera
• Members of this phylum are commonly known as
sponges. Mostly marine, asymmetrical and have
cellular level of organization.
• They have water transport or canal system. Water
enters through minute pores, Ostia into central cavity
Spongocoel, from where it goes out through Osculum.
• Nutrition, respiration and excretion is performed by
pathway of water transport system.
• Skeleton made up of spicules or spongin fibres.
• Egg and sperms are produced by same organism
(hermaphrodite). Asexual reproduction by
fragmentation and sexual reproduction by gametes
formation.
• Fertilisation internal and development is indirect.
• Example– Sycon, Spongilla.

10. Phylum – Coelenterata (Cnidaria)
• They are aquatic, mostly marine, sessile,
free swimming, radially symmetrical
animals.
• They exhibit tissue level of organization,
diploblastic, coelomate with single
opening.
• They show two types of body called polyp
and medusa.
• Polyp is sessile, fixed, and cylindrical,
without gonads. Example: Hydra,
Adamsia. Medusa is free swimming,
umbrella like having gonads like Aurelia
and Jelly fish.
• Some cnidarians exhibits both forms
(Obelia). Polyp produce medusa asexually
and medusa produce polyp sexually.

11. Phylum – Ctenophora
• Commonly known as the Comb
Jellies or Sea Walnuts.
• Exclusively marine,
diploblastic, radially
symmetrical, with tissue level of
organization.
• Body bears eight ciliated comb
plates which help in
locomotion.
• Bioluminescence (to emit light)
is present in Ctenophores.
• Are Hermaphrodite,
fertilisation is external,
development indirect.
• Example- Ctenoplana,
Pleurobranchia.

12. Phylum – Platyhelminthes
• They have dorso-ventrally flattened body, hence are
called flatworms. Endoparasites found in animals
including human beings
• Bilaterally symmetrical, triploblastic and
acoelomate animals with organ level of organization
• Hooks and suckers are present in the parasitic forms
• Some of them absorb nutrients from the host
directly through their body surface
• Flame cells help in osmoregulation and excretion
• Sexes are not separate. Fertilization is internal and
development is through many larval stages
• Some members like Planaria possess high
regeneration capacity
• Examples: Taenia (Tapeworm), Fasciola (Liver
fluke).

13. Phylum – Aschelminthes
• They may be free-living, aquatic,
terrestrial or parasitic in plants or
animals.
• Bilaterally symmetrical,
triploblastic, pseudo coelomate.
• Alimentary canal is complete with
well-developed muscular pharynx.
• They are Dioecious. Females are
longer than male.
• Example- Ascaris (round worm),
Wucheriria(filarial worm),
Ancyclostoma.

14. Phylum – Annelida
• Aquatic or terrestrial, bilaterally
symmetrical, segmented with organ
system level of organization.
• Aquatic Annelids like Nereis
possesses lateral appendages
parapodia, for swimming. Nephridia
help in osmoregulation and
excretion.
• Neural system consists of paired
ganglia connected by lateral nerves
to a double ventral nerve cord.
• Dioecious (Nereis) or monocious
(earthworm, leech)
• Example- Pheretima (earthworm),
Hirunidaria (Blood sucking leech).

15. Phylum – Arthropoda
• Largest phylum of animals which includes insects.
They have organ system of organization. They are
triploblastic, coelomate, bilaterally symmetrical
with chitinous exoskeleton.
• Body consists of head, thorax and abdomen,
jointed appendages (jointed feet). Respiratory
organs are gills, book lungs or tracheal system
with open circulatory system.
• Excretion through malpighian tubules, sense
organs antenna or eyes. Fertilisation internal,
mostly oviparous. Examples:
 Economically important – Apis (honey bee),
Bombyx (silk worm).
 Vectors – Anopheles, Ades, Culex (mosquito).
 Living fossils – Limulus (king crab)

16. Phylum – Mollusca
• Terrestrial or aquatic, organ level of organization, bilaterally
symmetrical, triploblastic and coelomate.
• Body divided into head, muscular foot and visceral hump.
Unsegmented and covered with calcareous shell.
• Feather like gills are present between hump and mantle.
• Mouth contains file like rasping organ for feeding called radula.
• Example- Pila, Octopus.

17. Phylum – Echinodermata
• Endoskeleton of calcareous ossicles, marine with organ system of
organization.
• Triploblastic, coelomate, presence of water vascular system help
in locomotion, capture of food and respiration.
• Sexes are separate, fertilisation is external and development is
indirect.
• Example- Asterias (Star fish), Cucumaria (Sea cucumber),
Antedon (Sea lily).

18. Phylum – Hemichordata
• Worm-like marine animals
with organ system of
organization, bilaterally
symmetrical, triploblastic and
coelomate animals.
• Body is cylindrical, composed
of anterior proboscis, a collar
and a long trunk.
• Open circulatory system,
respiration by gills, excretory
organ is proboscis glands.
• Sexes are separate, fertilisation
external, indirect development.
• Example- Balanoglossus,
Saccoglossus..

19. Phylum – Chordata
• Presence of notochord, have dorsal hollow nerve chord and
paired pharyngeal gill slits.
• Bilaterally symmetrical, triploblastic, coelomate with organs
system levels of organization.
• Closed circulatory system, ventral heart, post-anal tail is present.

20. Comparison of Chordates and Non-chordates
• In Urochordata, notochord is present only in larval tail.
In Cephalochordate it extends from head to tail and persists
throughout the life.
• Vertebrata possesses notochord in embryonic period which is
replaced by vertebral column in the adults.
• Sub-phylum Vertebrata is further divided into two
division Agnatha (lacks jaw) and Gnathostomata ( bears jaw).
• Gnathostomata is further divided into two super class- Pisces
(bears fins) and Tetrapoda (bears limbs)

21. Vertebrata - Devision

22. Class Cyclostomata (Circular mouthed fishes)
• They are ectoparasites on some
fishes. They have sucking and
circular mouth without jaws.
• Body devoid of scales, gill slits
for respiration, cranium and
vertebral column is
cartilaginous.
• Circulation is closed type. They
are marine but migrate to fresh
water for spawning and die
after few days. Larva return to
seas after metamorphosis.
• Example– Petromyzon
(Lamprey), Maxine (Hag fish).

23. Class Chondrichthyes (The Cartilaginous Fish)
• They are marine, streamlined body, have
cartilaginous endoskeleton, cold blooded,
tough skin with minute placoid scales.
• Gill slits are separate without operculum.
• They have powerful jaw and are predators.
• Air bladder is absent, hence to avoid sinking
swims constantly. Heart is two chambered,
cold blooded (Poikilothermous).
• Sexes separate. Males have pelvic fins which
bear claspers. Internal fertilisation, many are
viviparous.
• Electric organ is present in Torpedo and
Poison sting in Trygon
• Example- Scoliodon (Dog fish), Carcharodron
(great white shark).

24. Class Ostechthyes (The body fish)
• Marine and fresh water both
have bony endoskeleton.
Streamlined body with four pair
of gills covered by operculum.
• Skin is covered with scales, air
bladder is present, and heart is
two chambered, cold blooded.
• Sexes are separate, fertilisation
external, oviparous and
development direct.
• Example: Marine-
Hippocampus (Sea horse),
Exocoetus (Flying fish). Fresh
water- Labeo (Rohu), Catla
,Clarias (Magur).

26. Class Amphibia
• As the name indicates (Gr., Amphi : dual, bios, life), amphibians
can live in aquatic as well as terrestrial habitats.
• Most of them have two pairs of limbs.
• Body is divisible into head and trunk. Tail may be present in some.
• The amphibian skin is moist (without scales).
• The eyes have eyelids. A tympanum 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 threechambered (two auricles and one ventricle).
• These are cold-blooded animals. Sexes are separate. Fertilisation
• is external. They are oviparous and development is indirect.
• Examples: Bufo (Toad), Rana (Frog), Hyla (Tree frog),
Salamandra (Salamander), Ichthyophis (Limbless amphibia).

27. Class Amphibia

28. Class Reptilia
• The class name refers to their creeping or crawling mode of
locomotion (Latin, repere or reptum, to creep or crawl). They are
mostly terrestrial animals and their body is covered by dry and
cornified skin, epidermal scales or scutes.
• They do not have external ear openings. Tympanum represents ear.
• Limbs, when present, are two pairs.
• Heart is 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 is direct.
• 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).

29. Class Reptilia

30. Class Aves
• The characteristic features of Aves (birds) are the presence of
feathers and most of them can fly except flightless birds (e.g.,
Ostrich).
• They possess beak. 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 lungs. Air sacs connected to lungs supplement
respiration. Sexes are separate. Fertilisation is internal. They are
oviparous and development is direct.

31. Class Aves
• Examples : Corvus (Crow), Columba (Pigeon), Psittacula (Parrot),
Struthio (Ostrich), Pavo (Peacock), Aptenodytes (Penguin),
Neophron (Vulture).

32. 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 live in water.
• The most unique mammalian characteristic is the presence
• of milk producing glands (mammary glands) by which the young
ones are nourished.
• They have two pairs of limbs, adapted for walking, running,
climbing, burrowing, swimming or flying.
• The skin of 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.

33. Class Mammalia
• 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).