DIVERSITY AMONG ANIMALS
→ Criteria of
animal classification
Kingdom Animalia
is divided into 33 groups called phyla. But only nine major phyla will be
studied.
1. Phylum Porifera.
2. Phylum Cnidaria
3. Phylum
Platyhelminthes.
4. Phylum
Aschelminthes.
5. Phylum Annelida.
6. Phylum Mollusca.
7. Phylum
Arthropoda.
8. Phylum
Echinodermata.
9. Phylum Chordata.
·
This classification or grouping of animals is called taxonomy
or systematics.
1-Classification
on the basis of presence or absence of tissues:
All animals
are multicellular and eukaryotic. These cells form tissues, tissue forms organs
and organs into organ systems into organisms, only porifera are grouped into a
separate subkingdom of Parazoa. Because its members lack real tissues.
The remaining 8 phyla consisting of subkingdoms are Eumetazoa (true
metazoans).
• Tissues
organized into organs in (lower group).
• Organs to
organ system in (higher forms)
2-
Classification based on no. of tissue layers:
Animals are
established on the basis of tissue layers. A total of 3 germ issue layers is
seen on most animal embryos. They are of 2 types.
(i)
Diploblastic: Animals
with 2 germs layers namely ectoderm & endoderm. They have tissue level of
organization
Ø e.g: Cnidarians.
(ii)
Triploblastic: Animals
with 3 germ layers namely, echinoderm, mesoderm & endoderm. They have organ
& system level of organization.
Ø e.g: Platyhelminthes to Chordata.
3-
Classification based on Symmetry:
Symmetry: shape Asymmetry:
No shape/irregular.
·
The Eumetazoans are divided into 2 groups on the basis
of symmetry.
(i)
Radial symmetry(two equal halves)
A radial animal has a top
and bottom, or oral and aboral sides, but no head and hind end, and no left and
right sides.
Ø e.g: Phylum Cnidaria, Phylum Echinodermata.
·
Animals of this group are collectively called Radiata.
(ii)Bilateral
symmetry(equal half/Mirror)
A bilateral animal not
only has a dorsal (top) side and a ventral (bottom) side, but also a front
(head) end and a back (tail) end, and left and right sides.
Ø e.g: Phylum Platyhelmithes.
·
Animals of this group are collectively called Bilateria.
4-Classification
based on Coelom(Body Cavity)
The bilaterally
symmetrical animals are classified into 3 group on the basis of coelom (body
cavity).
(i) Acoelomate (No Cavity)
Simple animals such as flatworms
which lack any internal space or coelom between the body wall & their gut.
Ø e.g: Platyhelminthes.
(ii)Pseudocoelomates (False Feet)
Animal such as round worms have a
cavity through it is incompletely lined with mesoderm There is a byer of
mesoderm beneath the body wall but not around gut.
Ø e.g: Aschelminthes.
(iii)Coelomates (Cavity present)
Animals that have a true body
cavity or coelom that is completely lined with mesoderm.
Ø e.g: Animals from Annelids-Chordates.
·
It is of two types.
Blastospore: The site of invagination during
development.
(1)
Protostome:
When blastospore is associated
with mouth the animal is a protostome.
Ø e.g: Annelids, Molluscs & Arthropoda.
(2)Deutrostome:
When the
blastospore is associate with anus & second opening becomes the mouth the
animal is deutrostome.
Ø e.g: Echinodermates, Hermichordates & Chordates.
