Chapter 4 Animal Kingdom

Common Fundamental characteristics are considered for the purpose of classification of animals.

If we consider specific characteristics, then each organism will be placed in a separate group and the entire objective of classification would not be achieved.

Classification of animals is also important in comparing different organisms and judging their individual evolutionary significance. If only a single characteristic is considered, then this objective would not be achieved.

There is a certain common fundamental feature that helps in classification of living organisms. The features that can be used in classification for a given specimen are as follows.

On the basis of above features, we can easily classify a specimen into its respective category.

Coelom is a fluid filled space between the body wall and gut wall and lined by mesoderm on all of its sides. The presence or absence of body cavity or coelom plays a very important role in the classification of animals. Animals that possess a fluid filled cavity between body wall and digestive tract are known as coelomates. Annelids, mollusks, arthropods, echinodermates, and chordates are examples of coelomates. On the other hand, the animals in which the body cavity is not lined by mesoderm are known as pseudocoelomates. In such animals, mesoderm is scattered in between ectoderm and endoderm. Aschelminthes is an example of pseudocoelomates. In certain animals, the body cavity is absent. They are known as acoelomates. An example of acoelomates is platyhelminthes.

Taenia (Tapeworm) and Fasciola (liver fluke) are examples of parasitic platyhelminthes.

Peculiar features in parasitic platyhelminthes are as follows.

1. They have dorsiventrally flattened body and bear hooks and suckers to get attached inside the body of the host.

2. Their body is covered with thick tegument, which protects them from the action of digestive juices of the host.

3. The tegument also helps in absorbing nutrients from the host’s body.

The phylum Arthropoda consists of more than 75% of the animal species found on this earth. The reasons for the success of arthropods are as follows.

i. Jointed legs that allow more mobility on land

ii. Hard exoskeleton made of chitin that protects the body

iii. The hard exoskeleton also reduces water loss from the body of arthropods making them more adapted to terrestrial conditions.

Water vascular system is a characteristic feature of the phylum Echinodermata. It consists of an array of radiating channels, tube feet, and madreporite. The water vascular system helps in locomotion, food capturing, and respiration.

The characteristic features of the phylum Chordata include the presence of a notochord and paired pharyngeal gill slits. In sub-phylum Vertebrata, the notochord present in embryos gets replaced by a cartilaginous or bony vertebral column in adults. But in cephelochordates, notochord persists throughout life as such and in urochordates, notochord is present only in larval stages and absent in adults. Thus, it can be said that all vertebrates are chordates but all chordates are not vertebrates.

Gas bladder or air bladder is a gas filled sac present in fishes. It helps in maintaining buoyancy. Thus, it helps fishes to ascend or descend and stay in the water current.

Birds have undergone many structural adaptations to suit their aerial life. Some of these adaptations are as follows.

(i) Streamlined body for rapid and smooth movement

(ii) Covering of feathers for insulation

(iii) Forelimbs modified into wings and hind limbs used for walking, perching, and swimming

(iv) Presence of pneumatic bones to reduce weight

(v) Presence of additional air sacs to supplement respiration

The numbers of eggs produced by an oviparous mother will be more than the young ones produced by a viviparous mother. This is because in oviparous animals, the development of young ones takes place outside the mother’s body. Their eggs are more prone to environmental conditions and predators. Therefore, to overcome the loss, more eggs are produced by mothers so that even under harsh environmental conditions, some eggs might be able to survive and produce young ones. On the other hand, in viviparous organisms, the development of young ones takes place in safe conditions inside the body of the mother. They are less exposed to environmental conditions and predators. Therefore, there are more chances of their survival and hence, less number of young ones is produced as compared to the number of eggs produced by oviparous mother.

The body segmentation first appeared in the phylum, Annelida (annulus meaning little ring).

            Column I                              Column II

(a)       Operculum                (viii)   Osteichthyes

(b)       Parapodia                  (v)       Annelida

(c)       Scales                         (iv)      Reptilia

(d)       Comb plates              (i)        Ctenophora

(e)       Radula                        (ii)       Mollusca

(f)        Hairs                           (vii)    Mammalia

(g)       Choanocytes             (iii)     Porifera

(h)       Gill slits                     (vi)      Cyclostomata and Chondrichthyes