Chapter:09 Diversity Among Animals

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.