Point to Remember

Basis of Classification :
Animals are classified on the basis of following few fundamental features—
1. Levels of Organisation :
(1) Cellular level : Cells are arranged as loose cell aggregates, e.g.,sponges.
(2) Tissue level : The cells performing the same function are arranged into
tissues, e.g., Coelenterates.
(3) Organ level : Tissues are grouped together to form organs, each
specialised for a particular function. e.g., platyhelminthes.
(4) Organ system level : organs are associated to form functional systems
e.g., Annelids, Arthropods, Molluscs, Echinoderms and Chordates.
Example : Circulatory System.
Open type : Blood pumped out through heart. Not confined to blood vessels.
Cells and tissues are directly bathed in it.
Closed types : Blood is circulated through blood vessels (arteries,veins and
capillaries)
2. Symmetry :
Q Asymmetrical : Cannot be divided into equal halves through median plane

e.g., Sponges.
Q Radial symmetry : Any plane passing through central axis can divide organism

into identical halves. e.g., coelentrates,Ctenophores and echinoderms.

Q Bilateral symmetry : Only one plane can divide the organism into two identical

left and right halves e.g., Annelids and Arthropods.

3. Germinal Layers :
Diploblastic : Cells arranged in two embryonic layers i.e., external ectoderm
and internal endoderm. (Mesoglea may be present in between ectoderm and
endoderm) e.g., porifers and Coelentrates. (Cnidarians)
Triploblastic : Three layers present in developing embryo i.e., ectoderm,
mesoderm and endoderm. e.g., Platyhelminthes to Chordates.
 4. Coelom (Body cavity which is lined by mesoderm)
Coelomates : Have coelom e.g., Annelids, Arthropods, molluscs, Echinoderms,
Chordates etc.
Pseudocoelomates : No true coelem as mesoderm is present in scattered
pouches between ectoderm and endoderm. e.,g., Aschelminthes.
Acoelomates : Body cavity is absent e.g., Platyhelminthes.
5. Segmentation (A) True Metamerism : Found Annelida,Arthropoda,
Chordata :
Q Segmentation is external as well as a internal in Annelids.

 Q Segmentation is external in Arthropods.

Q Segmentation is internal in chordates.

Q Metamerism : If body is externally and internally divided into segments

(metameres) with serial repetition of atleast some organs, then phenomenon is

called metamerism e.g., Earthworm. (B) Pseudometamerism : Found in
tapeworm. The proglottids (segments of tapeworm) budded off from neck
not embryonic in origin.
6. Notochord :
Q Rod-like structure formed during embryonic development on t he dorsal side.

It is mesodermally derived e.g., Chordates.

Q Non-chordates do not have notochord .e.g., porifera to echinoderms.

Phylum Porifera :
Q Also called sponges.
Q Are usually marine and asymmetrical.
Q Have cellular level of organisation and diploblastic animals.
Q Food gathering, respiratory exchange and removal of wastes occurs through
water canal system. Digestion intracellular.
Q Ostia (minute pores on body), spongocoel (body cavity) and osculum help
in water transport. They are lined by choanocytes (collar cells).
Q Body wall has skeleton of spicules or spongin fibres.
Q Animals are hermaphrodite. Fertilisation internal. Development is indirect
(i.e., has a larval stage distinct from adult stage) e.g., Sycon, Euspongia.
Spongilla (Fresh water sponge)
Phylum Coelenterata :
Q Also called Cnidarians.
Q Are usually marine and radially symmetrical.
Q Sessile or free swimming.
 Q Have tissue level of organisation.
Q Are diploblastic (with mesogloea)

Q Capture of prey, anchorage and defence occurs through cnidoblasts/cnidocytes

(have stinging capsules nematocytes) present on tentacles.

Q Digestion extracellular and intracellular.

Q Have a central gastro-vascular cavity and an opening, hypostome.

Q Body wall of some composed of calcium carbonate. e.g. corals.

Q exhibit two body forms : polyp and medusa e.g., Hydra, Aurelia.

Q Alternation of generation between body forms called metagenesis ocurs in

Obelia where :

Medusa Polyp. (Sessile and cylindrical)

(free swimming &
umbrella shaped)
Q e.g., Physalia, Adamsia, Pennatula, Gorgonia,Meandrina.
Phylum Ctenophora :
Q Also called as sea walnuts or comb jellies.
Q Are exclusively marine, radially symmetrical.
Q Have tissue level organisation, are diploblastic.
Q Digestion both extra and intracellular.
Q Body has eight external rows of ciliated comb plates for locomotion.
Q Show Bioluminescence (Property of living organisms to emit light).
Q Hermaphrodite (sexes are not separate).
Q Only sexual reproduction occurs. Exernal fertilization. Indirect development.
e.g., Ctenoplana, Pleurobrachia.
Phylum Plathyhelminthes :
Q Also called as ‘flat worms’.
Q Have dorsoventrally flattened body. Are mostly endoparasites in animals.
Q Are bilaterally symmetrical, triploblastic, acoelomate,with organ level of
orgnisation.
Q Absorb nutrients through body surface.
Q Parasitic forms have hooks and suckers.
Q ‘Flame cells’ help in osmoregulation and excretion.
 Q Sexes not separate.
Q Fertilisation internal. Many larval stages present. Planaria has high
regeneration capacity. e.g., Taenia, Fasciola.
Phylum Aschelminthes :
Q Also called ‘round worms’.
Q May be free living, parasitic, aquatic or terrestrial.
Q Are bilaterally symmetrical, triploblastic, pseudocoelomate.
Q Alimentary canal complete (has muscular pharynx), wastes removed through
excretory pore.
Q Sexes separate. (dioecious)
Q Females longer than males.
Q Fertilisation internal. Development direct or indirect. e.g., Ascaris,Wuchereria,
Ancylostoma.
Phyum Annelida :
Q Are aquatic or terrestrial, free-living or parasitic.
Q Are bilaterally symmetrical, triploblastic, organ-system level of organisation
and metamerically segmented body.
Q Are coelomate animals.
Q Have longitudinal and circular muscles for locomation.
Q Have closed circulatory system.
Q Nereis (dioecious and aquatic annelid) has lateral appendages called parapodia
for swimming.
Q Have nephridia for osmoregulation and excretion.
Q Neural system consists of paired gangila connected by lateral nerves to a
double ventral nerve cord.
Q Reproduction is sexual.
Q e.g., Earthworm (Pheretima) and Leech (Hirudinaria) which are hermaph
rodites (i.e., monoecious).
Phylum Arthropoda :
Q Largest phylum of Animalia.
Q Are bilaterally symmetrical, triplobastic, segmented externally and organ
system level of organisation, coelomate.
Q Body divisible into head, thorax, abdomen and has a chitinous exoskeleton.
Jointed appendages are present.
 Phylum –
CHORDATA

Sub Phylum – Urochordata Cephalochordata Vertebrata

Division

Agnatha Gnathostomata

Super Class

Pisces Tetrapoda

1. Chondrichthyes 1. Amphibia
Class Cyclostomata
2. Osteichthyes 2. Reptilia
3. Aves
4. Mammalia
 Q Respiration by gills, book gills, book lungs or tracheal system. Excretion
through malpighian tubules.
Q Sensory organs : Antennae, eyes; Organs of balance : Statocysts.
Q Fertilisation usaully internal. Development is indirect or direct. Are mostly
oviparous.
e.g., Apis, Bombyx, Laccifer, Anopheles, Culex, Aedes, Locusta, Limulus.
Phulum Mollusca :
Q Second largest phylum of Animalia.
Q Terrestrial or aquatic
Q Are bilaterally symmetrical, triplobastic and organ system level of organisation,
coelomate.
Q Body vidisble into head, muscular foot and visceral hump and is covered
by calcareous shell and is unsegmented.
Q Mantle : Soft and spongy layer of skin; Mantle cavity : Space between
visceral hump and mantle.
Q Respiration and excretion by feather like gills in mantle cavity.
Q Head has sensory tentacles. Radula a rasping organ for feeding in mouth.
Q Are oviparous, dioecious, have indirect development.
e.g., Plia, Pinctada, Octopus, Sepia, Loligo, Aplysia, Dentalium, Chaetopleura.
Phylum Echinodermata :
Q Are spiny bodied organisms with endoskeleton of calcareous ossicles.
Q Are exclusively marine, radially symmetrical in adult but bilaterally
symmetrical in larval stage. Organ system level of organisation.
Q Triploblastic and coelomate.
Q Digestive system complete. Mouth ventral, Anus on dorsal side.
Q Food gathering, respiration, locomotion carried out by water vascular system.
Q Excretory system is absent.
Q Reproduction–sexual, sexes are separate.
Q Fertilisation external. Development indirect (free swimming larva)
Q e.g., Asterias, Cucumaria, Antedon, Echinus, ophiura.
Phylum Hemichordata :
Q Represents small group of worm-like organisms.
Q Was earlier placed as sub-phylum of Phyum Chordata.
 Q Bilaterally symmetrical, triploblastic and coelomate with organ system level
of organisation.
Q Body cylindrical, has proboscis, collar and trunk.
Q Circulatory System–open.
Q Respiration by gills, excretion by proboscis gland.
Q Sexes separate, external fertiliastion, indrect development.
e.g, Balanoglossus, Saccoglossus.
Phylum Chordata :
Q Presence of Notochord.
Q Have dorsal hollow nerve cord.
Q Have paired pharyngeal gill slits.
Q Bilaterally symmetrical, triploblastic, coelomate, organ system level of
organisation.
Q Heart is ventral.
Q Post anal tail present, closed circulatory system.
(i) Sub-Phyla Urochordata /Tunicata
Q Notocohord present only in larval tail.
e.g., Ascidia, Salpa, Doliolum
(ii) Sub-phyla Cephalochordata
Q Notochord extends from head to tail (Persistent)
e.g., Amphioxus.
(iii) Sub-Phyla Vertebrata
Q Have notochord only during embryonic period.
Q Notochord gets replaced by bony or cartilaginous vertebral column.
Q Have ventral muscular heart, kidneys for excretion and osmoregulation, paired
appendages (fins or limbs)
Vertebrata have two Division :
(a) Agnatha (Lacks Jaw) : Class : Cyclostomata
Q Live as ectoparasites on some fishes.

Q Have sucking and circular mouth without jaws.

Q Have 6-15 paris of gill slits for respiration.

Q No scales, no paired fins.

Q Cranium and vertebral column is cartilagenous.

 Q Marine, Migrate to fresh water for spawning and die after spawning.
Q Larva returns to ocean after metamorphosis.

e.g., Petromyzon, Myxine

(b) Gnathostomata (Bear Jaws)–divides into two super classes :
Super-class : Pisces
1. Class : Chondrichthyes :
Q Have cartilagenous endoskeleton, are marine with streamlined body.

Q Mouth ventral.

Q Gill slits without operculum (gill cover).

Q Skin has placoid scales; jaws–very powerful.

Q No air bladder, so swim constantly to avoid sinking.

Q Teeth are backwardly directed, modified placoid scales.

Q Notochord is persistent throughout life.

Q Two chambered heart; poikilotherms (cold-blooded)

Q Sexes separate; males have claspers on pelvic fins.

Q Internal fertilisation; viviparous.

e.g., Tarpedo, Trygon, Scoliodon, Pristis, Carcharodon

2. Class : Osteichthyes
Q Have bony endoskeleton, Aquatic

Q Mouth is usually terminal. Body-Streamlined

Q Four pairs of gill slits covered by operculum, heart two chambered, cold

blooded.
Q Sking has cycloid/ctenoid scales.

Q Have air bladder which regulates buoyancy.

Q Sexes separate.

Q Usually oviparous, fertilisation external.

Q Development direct.

Q e.g., Hippocampus, Labeo, Catla, Betla, Clarias, Exocoetus

Sub-Phylum Vertebrata : Gnathostomata

Super Class : Tetrapoda
1. Class : Amphibia
Q Can live in aquatic as well as terrestrial habitats.

Q Body divisible into head and trunk, paired limbs.

 Q Skin moist. No scales.
Q Tympanum represents ear. Eyes have eyelids.

Q Cloaca is the common chamber where alimentary canal, urinary and

reproductive tracts open.

Q Respiration by gills, lungs or skin.

Q Heart is 3-chambered; cold-blooded; Sexes separate; fertilisation external.

Q Oviparous. Indirect development.

Q e.g., Bufo, Rana, Hyla, Salamandra, Ichthyophis

2. Class : Reptilla
Q Creep or crawl to locomote. Mostly terrestrial.

Q Body has dry and cornified skin and epideremal scales or scutes.

Q Tympanum represents ear.

Q Limbs, when present, are two pairs

Q Snakes and lizards shed scales as skin cast.

Q Heart 3-chambered but 4-chambered in crocodiles.

Q Sexes Separate; fertilisation internal.

Q Oviparous. Direct development.

Q e.g., Testudo, Naja, Vipera, Calotes, Crocodilus, Hemidactylus

3. Class : Aves
Q Presence of feathers except flightless birds and beak (modified jaws)

without teeth.
Q Forelimbs are modified into wings.

Q Hind limbs have scales, modified for walking, swimmng or clasping.

Q Skin is dry as no glands on skin except oil gland at base of tail.

Q Endoskeleton bony with air cavities (pneumatic) and hollow bones to

assist in flight.
Q Crop and Gizzard—Additional chamber in digestive tract.

Q Air sacs are connected to lungs to supplement respiration.

Q Warm blooded (homoiothermous), Heart–Four chambered.

  Q Sexes separate, fertilization internal

Q Oviparous. Direct development.

Q e.g., Columba, Struthio, Pavo, Corvus, Neophron, Pstittacula Aptenodytes.

4. Class : Mammalia
Q Have mammary glands to nourish young ones.
Q Have two pairs of limbs, adapted to perform special work.
Q Skin has hairs.
Q External ears or, pinna present.
Q Different types of teeth in jaw.
Q Homoiothermous; Heart–Four chambered, Lungs for respiration.
Q Sexes are separate, fertilisation internal.
Q Viviparous. Direct development.
Q e.g., Rattus, Canis, Elephas, Equus. Oviparous mammal is
Ornithorhynchus.

* For WB- Study classification of mammals- 3

features and 2 examples each of Prototheria,
Metatheria and Eutheria.
Ref. to Santra/any ref. book