Animals are multicellular and heterotrophic organisms a. Diploblastic animals: 2 germ layers- outer ectoderm and
without cell wall and chlorophyll. inner endoderm. In between these layers, an
Kingdom Animalia includes 11 major phyla: undifferentiated jelly-like layer called mesoglea is
1. Porifera 7. Arthropoda present. E.g. Cnidaria & Ctenophora.
2. Cnidaria 8. Mollusca b. Triploblastic animals: 3 germ layers- Outer ectoderm,
3. Ctenophora 9. Echinodermata middle mesoderm and inner endoderm. E.g.
4. Platyhelminthes 10. Hemichordata Platyhelminthes to Chordata.
5. Aschelminthes 11. Chordata
6. Annelida
BASIS OF CLASSIFICATION
(a) Diploblastic
1. Levels of organization (b) Triploblastic
Based on this, animals are grouped into four levels:
a. Cellular level of organization: Here, the cells are
arranged as loose cell aggregates. E.g. Porifera.
b. Tissue level of organization: Here, the cells are arranged 4. Coelom (body cavity)
into tissues. E.g. Cnidarians and Ctenophores. It is the cavity lined by mesoderm. It is seen between body
c. Organ level of organization: Here, tissues are arranged wall and gut wall. Coelom separates the muscles of gut and
into organs. E.g. Higher animals (Platyhelminthes to body wall.
chordates). Based on the nature of coelom, animals are 3 types:
d. Organ system level of organization: Here, organs are a. Acoelomate: No coelom. The space between body wall
associated to organ system. Each system performs a and digestive cavity is filled with matrix (parenchyma).
specific physiological function. E.g. Higher animals. E.g. Porifera to Platyhelminthes.
Organ systems of various animals show complexities. E.g. b. Pseudocoelomate: False coelom. Here, the body cavity is
Digestive system is 2 types: not lined by mesoderm. Mesoderm is scattered pouches.
o Incomplete: It has only a single opening that acts as E.g. Aschelminthes.
mouth & anus. Seen in Cnidaria and Platyhelminthes. c. Coelomate: True coelom. Here, the coelom arises from
o Complete: It has 2 openings (mouth & anus). the mesoderm. Coelom is lined by peritoneal layer and
Circulatory system is 2 types: open & closed. filled with coelomic fluid. E.g. Annelida to Chordata.
2. Body symmetry
It is the arrangement of similar body parts on 2 sides of main
axis of the body. Based on symmetry, animals are 2 types:
Asymmetrical and Symmetrical.
a. Asymmetrical: Here, body cannot be divided into 2 equal
halves. E.g. Most Poriferans, Snails etc.
b. Symmetrical: Here, body can be divided into 2 equal Coelomate Pseudocoelomate Acoelomate
halves. It is 2 types. Functions of coelom:
• Radial symmetry: Here, body can be divided into 2 • It accommodates visceral organs.
equal halves in any vertical plane along central axis • Coelomic fluid reduces friction between visceral organs.
(oral-aboral axis) of the body. E.g. some Poriferans, • It acts as shock absorber.
Cnidarians, Ctenophores and Echinoderms (adult).
• Bilateral symmetry: Here, body can be divided into
5. Metamerism (segmentation)
right & left halves in only one plane. It is the phenomenon in which the body or organs is
E.g. Platyhelminthes to Chordata (except adult externally and internally divided into repeated segments
Echinodermata). (metameres). E.g. Annelids (earthworm etc.), Arthropods.
The body of bilaterally symmetrical animal has a dorsal side 6. Notochord
(upper), a ventral side (lower), left & right lateral sides, It is a mesodermally derived supporting rod formed on the
anterior (cephalic) side and posterior (anal or tail) side. dorsal side during embryonic development in some animals.
3. Germinal layers (Embryonic layers) These are Animals with notochord are called chordates and those
layers of embryo from which all the body organs are without notochord are called non-chordates.
formed. Based on the number of germ layers, animals are 2
types- Diploblastic and Triploblastic.
1
, Ctenophora (Comb
Features Porifera (Sponges) Cnidaria (Coelenterata)
jellies or Sea walnuts)
Grades of
Cellular Tissue Tissue
organization
Symmetry Asymmetrical. Some are radial. Radial Radial
Germ layers - Diploblastic Diploblastic
Coelom Acoelomate Acoelomate Acoelomate
Aquatic (mostly marine). Aquatic (mostly marine).
Habit and Exclusively marine.
Sedentary. Sessile/free swimming.
habitat Solitary & pelagic
Solitary/colonial. Solitary/colonial.
Incomplete.
Digestive Absent. Incomplete.
Intracellular and
system Intracellular digestion. Intracellular & extracellular digestion.
extracellular digestion.
Respiratory
Absent Absent Absent
system
Circulatory
Absent Absent Absent
system
Asexual (fragmentation) & Polyp reproduces asexually (budding)
Only Sexual.
Sexual. and medusa sexually.
Hermaphrodite.
Reproduction Hermaphrodite. Most are separate sexes.
External fertilization.
Internal fertilization. External fertilization.
Development is indirect.
Development is indirect. Development is indirect.
Water canal (water Tentacles with cnidoblasts. Locomotion is by 8
transport) system. Gastro-vascular cavity (coelenteron) vertical external rows of
Millions of ostia (pores). with an opening (mouth) on hypostome. ciliated comb plates.
Unique
Spongocoel & canals are lined
features Polyp & Medusa forms are seen. Tentacles present.
with choanocytes (collar cells).
Some shows alternation of generation. Shows
Body is supported by spicules
Corals have skeleton (CaCO3). Bioluminescence.
and spongin fibres.
Hydra, Obelia, Aurelia, Physalia
Sycon (Scypha), (Portuguese man of war), Adamsia
Ctenoplana,
Examples Spongilla (fresh water sponge), (Sea-anemone), Pennatula (Sea pen),
Pleurobrachia
Euspongia (Bath sponge) Gorgonia (Sea fan),
Meandrina (Brain coral)
1. Water canal system: Here, water enters through minute pores (ostia) in the body wall into a central cavity (spongocoel), from
where it goes out through osculum. Canal system is used for food gathering, gas exchange and removal of wastes.
2. Hermaphrodite (Monoecious): Male and female sex organs are seen in same individual.
3. Tentacles: Finger-like structures which surrounds the mouth of coelenterates. Used for food capture & defense.
4. Cnidoblasts (Cnidocytes): These are stinging cells (present on the tentacles and the body) with a poison-filled capsule called
nematocyst. Cnidoblast is used for anchorage, defense and to capture prey.
5. Polyp & Medusa: 2 types of body forms in cnidarians.
Polyp is tubular attached asexual form, with upwardly directed mouth & tentacles. E.g. Hydra, Adamsia.
Medusa is umbrella like, free-swimming sexual form, with downwardly directed mouth & tentacles. E.g. Aurelia (Jelly fish).
6. Alternation of generation (Metagenesis): The phenomenon in which polyps produce medusae asexually and medusae form
the polyps sexually. E.g. Obelia.
7. Bioluminescence: It is the property of some animals to emit light from the body.
Cnidoblast Medusa Polyp
2
without cell wall and chlorophyll. inner endoderm. In between these layers, an
Kingdom Animalia includes 11 major phyla: undifferentiated jelly-like layer called mesoglea is
1. Porifera 7. Arthropoda present. E.g. Cnidaria & Ctenophora.
2. Cnidaria 8. Mollusca b. Triploblastic animals: 3 germ layers- Outer ectoderm,
3. Ctenophora 9. Echinodermata middle mesoderm and inner endoderm. E.g.
4. Platyhelminthes 10. Hemichordata Platyhelminthes to Chordata.
5. Aschelminthes 11. Chordata
6. Annelida
BASIS OF CLASSIFICATION
(a) Diploblastic
1. Levels of organization (b) Triploblastic
Based on this, animals are grouped into four levels:
a. Cellular level of organization: Here, the cells are
arranged as loose cell aggregates. E.g. Porifera.
b. Tissue level of organization: Here, the cells are arranged 4. Coelom (body cavity)
into tissues. E.g. Cnidarians and Ctenophores. It is the cavity lined by mesoderm. It is seen between body
c. Organ level of organization: Here, tissues are arranged wall and gut wall. Coelom separates the muscles of gut and
into organs. E.g. Higher animals (Platyhelminthes to body wall.
chordates). Based on the nature of coelom, animals are 3 types:
d. Organ system level of organization: Here, organs are a. Acoelomate: No coelom. The space between body wall
associated to organ system. Each system performs a and digestive cavity is filled with matrix (parenchyma).
specific physiological function. E.g. Higher animals. E.g. Porifera to Platyhelminthes.
Organ systems of various animals show complexities. E.g. b. Pseudocoelomate: False coelom. Here, the body cavity is
Digestive system is 2 types: not lined by mesoderm. Mesoderm is scattered pouches.
o Incomplete: It has only a single opening that acts as E.g. Aschelminthes.
mouth & anus. Seen in Cnidaria and Platyhelminthes. c. Coelomate: True coelom. Here, the coelom arises from
o Complete: It has 2 openings (mouth & anus). the mesoderm. Coelom is lined by peritoneal layer and
Circulatory system is 2 types: open & closed. filled with coelomic fluid. E.g. Annelida to Chordata.
2. Body symmetry
It is the arrangement of similar body parts on 2 sides of main
axis of the body. Based on symmetry, animals are 2 types:
Asymmetrical and Symmetrical.
a. Asymmetrical: Here, body cannot be divided into 2 equal
halves. E.g. Most Poriferans, Snails etc.
b. Symmetrical: Here, body can be divided into 2 equal Coelomate Pseudocoelomate Acoelomate
halves. It is 2 types. Functions of coelom:
• Radial symmetry: Here, body can be divided into 2 • It accommodates visceral organs.
equal halves in any vertical plane along central axis • Coelomic fluid reduces friction between visceral organs.
(oral-aboral axis) of the body. E.g. some Poriferans, • It acts as shock absorber.
Cnidarians, Ctenophores and Echinoderms (adult).
• Bilateral symmetry: Here, body can be divided into
5. Metamerism (segmentation)
right & left halves in only one plane. It is the phenomenon in which the body or organs is
E.g. Platyhelminthes to Chordata (except adult externally and internally divided into repeated segments
Echinodermata). (metameres). E.g. Annelids (earthworm etc.), Arthropods.
The body of bilaterally symmetrical animal has a dorsal side 6. Notochord
(upper), a ventral side (lower), left & right lateral sides, It is a mesodermally derived supporting rod formed on the
anterior (cephalic) side and posterior (anal or tail) side. dorsal side during embryonic development in some animals.
3. Germinal layers (Embryonic layers) These are Animals with notochord are called chordates and those
layers of embryo from which all the body organs are without notochord are called non-chordates.
formed. Based on the number of germ layers, animals are 2
types- Diploblastic and Triploblastic.
1
, Ctenophora (Comb
Features Porifera (Sponges) Cnidaria (Coelenterata)
jellies or Sea walnuts)
Grades of
Cellular Tissue Tissue
organization
Symmetry Asymmetrical. Some are radial. Radial Radial
Germ layers - Diploblastic Diploblastic
Coelom Acoelomate Acoelomate Acoelomate
Aquatic (mostly marine). Aquatic (mostly marine).
Habit and Exclusively marine.
Sedentary. Sessile/free swimming.
habitat Solitary & pelagic
Solitary/colonial. Solitary/colonial.
Incomplete.
Digestive Absent. Incomplete.
Intracellular and
system Intracellular digestion. Intracellular & extracellular digestion.
extracellular digestion.
Respiratory
Absent Absent Absent
system
Circulatory
Absent Absent Absent
system
Asexual (fragmentation) & Polyp reproduces asexually (budding)
Only Sexual.
Sexual. and medusa sexually.
Hermaphrodite.
Reproduction Hermaphrodite. Most are separate sexes.
External fertilization.
Internal fertilization. External fertilization.
Development is indirect.
Development is indirect. Development is indirect.
Water canal (water Tentacles with cnidoblasts. Locomotion is by 8
transport) system. Gastro-vascular cavity (coelenteron) vertical external rows of
Millions of ostia (pores). with an opening (mouth) on hypostome. ciliated comb plates.
Unique
Spongocoel & canals are lined
features Polyp & Medusa forms are seen. Tentacles present.
with choanocytes (collar cells).
Some shows alternation of generation. Shows
Body is supported by spicules
Corals have skeleton (CaCO3). Bioluminescence.
and spongin fibres.
Hydra, Obelia, Aurelia, Physalia
Sycon (Scypha), (Portuguese man of war), Adamsia
Ctenoplana,
Examples Spongilla (fresh water sponge), (Sea-anemone), Pennatula (Sea pen),
Pleurobrachia
Euspongia (Bath sponge) Gorgonia (Sea fan),
Meandrina (Brain coral)
1. Water canal system: Here, water enters through minute pores (ostia) in the body wall into a central cavity (spongocoel), from
where it goes out through osculum. Canal system is used for food gathering, gas exchange and removal of wastes.
2. Hermaphrodite (Monoecious): Male and female sex organs are seen in same individual.
3. Tentacles: Finger-like structures which surrounds the mouth of coelenterates. Used for food capture & defense.
4. Cnidoblasts (Cnidocytes): These are stinging cells (present on the tentacles and the body) with a poison-filled capsule called
nematocyst. Cnidoblast is used for anchorage, defense and to capture prey.
5. Polyp & Medusa: 2 types of body forms in cnidarians.
Polyp is tubular attached asexual form, with upwardly directed mouth & tentacles. E.g. Hydra, Adamsia.
Medusa is umbrella like, free-swimming sexual form, with downwardly directed mouth & tentacles. E.g. Aurelia (Jelly fish).
6. Alternation of generation (Metagenesis): The phenomenon in which polyps produce medusae asexually and medusae form
the polyps sexually. E.g. Obelia.
7. Bioluminescence: It is the property of some animals to emit light from the body.
Cnidoblast Medusa Polyp
2
