Animal Classification Science Notes

Important Points :

  • The living organisms are classified according to their basic characteristics, such as presence or absence of nucleus, unicellular body or multicellular body, presence or absence of cell wall and the mode of nutrition in them.

→ The plants are classified according to the following basis :

  • Presence or absence of the organs.
  • Presence or absence of separate conducting tissues for the conduction of food and water.
  • Presence or absence of seeds in plants.
  • Whether seeds are enclosed in fruits or not.
  • Number of cotyledons in seeds : one or two.

Classification :

  • There is great diversity among the animals on the earth. There are about 7 million species of
    different animals.
  • Depending upon the similarities and differences among these animals, they have been classified. Such systematic classification makes it easy to study the great diverse animal forms.

Animal Classification Science Notes

History of animal classification :

→ To summarize the history of classification :

Scientist/Taxonomist Basis for classification Method
Greek philosopher Aristotle Theophrastus, Pliny, John Ray, Linnaeus Body size, habits and habitats ‘Artificial method’
Dobzhansky and Meyer Body organization, types of cells, chromosomes, bio-chemical properties Natural system of classification
Oarl Woese Presence or absence of notochord Method based on evolution Traditional method

Animal Classification Science Notes

→ Benefits of animal classification

  • By placing the animals in proper classified groups, their study becomes convenient.
  • By studying few animals from each group understanding the entire group becomes easy.
  • Animal classification leads to better understanding of animal evolution.
  • Identification of animals can be done with great accuracy.
  • The relationship of animals with other living organisms is better understood.
  • The habitat of each animal and it’s exact role in the nature can be understood by learning animal classification.
  • Various adaptations of animals can be studied.

→ Traditional method of animal classification :

Animal classification : Formation of groups and sub-groups of animals by taking into account their similarities and differences is called animal classification.

→ The gross difference between non-chordates and chordates :

Point of difference Non-chordates Chordates
Notochord Absent Present
Pharyngeal Gill slits Absent Present
Nerve cord Ventral, solid and paired Dorsal, hollow and single
Heart Dorsally located Ventrally located

Animal Classification Science Notes

→ Classification of Non-chordates into ten phyla :

  • Protozoa (Protista)
  • Porifera
  • Coelentarata/Cnidaria
  • Platyhelminthes
  • Aschelminthes
  • Annelida
  • Arthropoda
  • Mollusca
  • Echinodermata
  • Hemichordata

→ Chordates: All chordate animals belong to the single group which is called Chordata. Chordata has three subphyla, viz.

  • Urochordata
  • Cephalochordata
  • Vertebrata
  • Sub-phylum Vertebrata is further divided into following six classes as –
  • Cyclostomata
  • Pisces
  • Amphibia
  • Reptilia
  • Aves
  • Mammalia

→ Robert Whittaker has given five kingdom classification system. All the multicellular, heterotrophic organisms are included under kingdom Animalia or Animal kingdom.

Animal Classification Science Notes

→ According to this system the criteria for classification are as follows:

  • Body organization
  • Body symmetry
  • Body cavity
  • Germinal layers
  • Segmentation

New (method) system of animal classification :

Criteria for new system of classification:

→ Grades of organization: Unicellular organisms have a single cell. But in multicellular animals ther are many cells.

Grades of organization Information Examples
Protoplasmic grade organization Body made up of only protoplasm. Unicellular animals.
Cellular grade organization Many cells are present. But tissues are not formed. Porifera.
‘Cell-tissue grade’ organization Cells performing similar function form the tissues. Tissues perform all body functions. Cnidaria.
‘Tissue-Organ grade’ organization Tissues are organized to form some organs. But complete organ systems are not formed. Flat worms.
‘Organ-system grade’ organization Different organs form organ system to perform specific functions in the body. Human beings and all other higher animals.

Animal Classification Science Notes

Body symmetry:

Body symmetry Information Examples
Asymmetrical No imaginary axis can divide the body into two equal halves. Amoeba, Paramoecium, some sponges.
Radial Symmetry An imaginary cut passing through central axis in any plane of body, gives two equal halves. Thus, five different planes passing through central axis of body can divide the body into two equal halves. Star fish and other echinoderms.
Bilateral symmetry Only one imaginary axis passing through the body divides it into two equal halves. Insects, fishes, frog, birds, human.

Animal Classification Science Notes

Germinal layers :

Condition of Germinal layers Information Examples
Diploblastic Two germinal layers, ectoderm and endoderm present. Coelenterata/Cnidaria.
Triploblastic Three germinal layers, ectoderm, mesoderm and endoderm present. All other animals.

Body cavity:

Condition of body cavity Information Examples
Eucoelomate Body cavity present. During initial embryonic development period body cavity is formed from either mesoderm or gut. All animal phyla from Annelida to higher phyla.
Acoelomate Absence of coelom. Porifera, Cnidaria and Platyhelminthes.
Pseudocoelomate Body cavity is present but it is not formed by the mesoderm or gut. Hence it is not true coelom. Aschelminthes.

Animal Classification Science Notes

→ Segmentation : Segmentation is the phenomenon in which the body of animals is divided into segments
which are small, similar units. Body with segments is segmented body. E.g. Phylum Annelida shows segmented bodied animals. For non-chordate phyla, refer to the chart.

Kingdom Animalia :

  • Non-chordate animals :
  • Classification of Subphylum : Vertebrata

→ Chordates :

Phylum – Chordata Animals having a supporting notochord in their body are called Chordates.

→ Characters of phylum Chordata :

  • Presence of notochord in the body either throughout the life or at least in the developmental stage.
  • Presence of pharyngeal gill slits. (at least during developmental stage).
  • Presence of single, tubular and dorsal spinal cord.
  • Presence of ventrally situated heart.
  • Depending on the notochord, the Phylum chordata is classified into three subphyla.
  • Urochordata, Cephalochordata and Vertebrata/Craniata

→ Subphylum – Urochordata

  • Urochordates are animals having notochord only in tail region of larvae.
  • Marine, sedentary adults.
  • Larvae are free swimming, they metamorphose into sedentary adults.
  • Body is covered by test or tunic. This is a covering like a skin.
  • Hermaphrodite animals.
  • Examples: Herdmania, Doliolum, Oikopleura, etc.

Animal Classification Science Notes

→ Subphylum – Cephalochordata

  • Notochord is present in entire body length
  • Small, fish-like, marine animals.
  • Large pharynx having gill-slits.
  • Unisexual animals.
  • Example : Amphioxus.

→ Subphylum – Vertebrata/Craniata

For classification of Vertebrata refer to the chart.

  • Vertebrata has been divided into six classes.
  • This information has been given in the chart.

Science Notes