Coelom
❑ Coelom: The coelom is the fluid-filled body cavity present between the alimentary
canal and the body wall.
The coelom is one of the characteristic features of metazoans. The true coelom is a body
cavity formed during embryo development from the three germinal layers. The body
cavity meaning a fluid filled space that can accomodate organs. The coelom is lined by
mesodermal epithelium cells. Presence or absence of coelom is one of the criteria for
classifying animals.
The animal kingdom is divided into three groups on the basis of the nature of
coelom.These are
A) Eucoelomate or coelomate
B)pseudocoelomat
C) Acoelomate
1. Acoelomate:
Coelom is absent. The blastocoel is completely occupied by mesoderm. There is only
spongocoel or coelenteron present.
Example: Porifera, Coelenterata and Flatworms (Platyhelminthes).
,2. Pseudocoelomate:
True coelom is not present. The blastocoel is partly filled by mesodermal cells. The
body cavity is lined by mesoderm only towards the body wall and mesoderm is not
present towards the gut.
Example: Roundworms (Aschelminthes)
3. Eucoelomate:
Animals that have a true coelom. The coelom is lined by mesoderm on both the sides,
towards the body wall and towards the gut. The blastocoel present in the gastrula gets
completely replaced by a true coelom. The body organs are suspended in the coelom
by mesenteries.
Example: from the phylum Annelida to Chordata.
Eucoelomates are further divided into Protostomes and Deuterostomes on the basis
of different embryonic development. The process of coelom formation in protostomes
and deuterostomes is different. The coelom is categorised into two types on the basis of
formation, namely, Schizocoelom and Enterocoelom.
A. Schizocoelom: It is present in the protostomes. The body cavity or coelom
originates from the splitting of the mesoderm. One part attaches to ectoderm
and the other surrounds the endoderm. The space between them develops
into the coelom. The blastopore forms the mouth. Examples of
schizocoelous animals are Annelida, Arthropoda and Mollusca. In
Arthropoda and Mollusca the coelom is filled by blood and is known as
Haemocoel.
B. Enterocoelom: It is present in the deuterostomes. The coelom is formed
from the fusion of the internal outgrowths of the archenteron, that pinches
, off and fuses together to form coelom lined by mesoderm. Examples of
enterocoelous animals are Echinodermates and Chordates.
Functions of Coelom
1) Coelom works as a shock absorber and protects from any kind of mechanical
shock. It gives more flexibility to the body organs to move and protects from any
damage on minor bends by cushioning the internal organs
2) The coelomic fluid acts as a hydrostatic skeleton, which helps in the locomotion
of soft-bodied animals and gives the body a definite shape. Contracting muscles
can push against the coelomic fluid because of the fluid pressure.
3) The coelomocyte cells, that either float freely in the coelom or attached to the
wall, support the immune system. They support the immune system by initiating
humoral immune response and phagocytosis
4) The coelomic fluid also helps in gaseous transport and transport of nutrients and
waste products
5) Coelom gives the extra space required by organs to develop and function. E.g.
pumping action of the heart, carrying a child in the womb, etc. is possible due to
coelom
❑ Coelom: The coelom is the fluid-filled body cavity present between the alimentary
canal and the body wall.
The coelom is one of the characteristic features of metazoans. The true coelom is a body
cavity formed during embryo development from the three germinal layers. The body
cavity meaning a fluid filled space that can accomodate organs. The coelom is lined by
mesodermal epithelium cells. Presence or absence of coelom is one of the criteria for
classifying animals.
The animal kingdom is divided into three groups on the basis of the nature of
coelom.These are
A) Eucoelomate or coelomate
B)pseudocoelomat
C) Acoelomate
1. Acoelomate:
Coelom is absent. The blastocoel is completely occupied by mesoderm. There is only
spongocoel or coelenteron present.
Example: Porifera, Coelenterata and Flatworms (Platyhelminthes).
,2. Pseudocoelomate:
True coelom is not present. The blastocoel is partly filled by mesodermal cells. The
body cavity is lined by mesoderm only towards the body wall and mesoderm is not
present towards the gut.
Example: Roundworms (Aschelminthes)
3. Eucoelomate:
Animals that have a true coelom. The coelom is lined by mesoderm on both the sides,
towards the body wall and towards the gut. The blastocoel present in the gastrula gets
completely replaced by a true coelom. The body organs are suspended in the coelom
by mesenteries.
Example: from the phylum Annelida to Chordata.
Eucoelomates are further divided into Protostomes and Deuterostomes on the basis
of different embryonic development. The process of coelom formation in protostomes
and deuterostomes is different. The coelom is categorised into two types on the basis of
formation, namely, Schizocoelom and Enterocoelom.
A. Schizocoelom: It is present in the protostomes. The body cavity or coelom
originates from the splitting of the mesoderm. One part attaches to ectoderm
and the other surrounds the endoderm. The space between them develops
into the coelom. The blastopore forms the mouth. Examples of
schizocoelous animals are Annelida, Arthropoda and Mollusca. In
Arthropoda and Mollusca the coelom is filled by blood and is known as
Haemocoel.
B. Enterocoelom: It is present in the deuterostomes. The coelom is formed
from the fusion of the internal outgrowths of the archenteron, that pinches
, off and fuses together to form coelom lined by mesoderm. Examples of
enterocoelous animals are Echinodermates and Chordates.
Functions of Coelom
1) Coelom works as a shock absorber and protects from any kind of mechanical
shock. It gives more flexibility to the body organs to move and protects from any
damage on minor bends by cushioning the internal organs
2) The coelomic fluid acts as a hydrostatic skeleton, which helps in the locomotion
of soft-bodied animals and gives the body a definite shape. Contracting muscles
can push against the coelomic fluid because of the fluid pressure.
3) The coelomocyte cells, that either float freely in the coelom or attached to the
wall, support the immune system. They support the immune system by initiating
humoral immune response and phagocytosis
4) The coelomic fluid also helps in gaseous transport and transport of nutrients and
waste products
5) Coelom gives the extra space required by organs to develop and function. E.g.
pumping action of the heart, carrying a child in the womb, etc. is possible due to
coelom
