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Animal Biology - Introduction

Animal Biology

An animal – a living organism – is mobile and having heterotrophic mode of nutrition. There are various species of animals, which includes animals from unicellular protozoan to the highest mammals. They contains eukaryotic cells and do not possess thick cell wall.

They show well developed organ system and further classified based on the extent and type of the body design differentiation found.

As per Whittaker classification, all animals are included in Eukaryotic kingdom, which is further divided into Protista and Metazoan. Animals are either unicellular or multicellurar. Unicellular animals are amoeba and paramecium. Multicellular animals are further divided into parazoa and eumetazoa.

Organisms with holes and attached with solid support. They are non-mobile and holes all over the body leads to a canal system that helps in circulating water throughout the body to bring in food and oxygen. They are covered with a hard outside layer or skeleton. They do not show division of labor or organ formation.

The body design involves very minimal differentiation and division into tissues and commonly called as sponges. They are mainly found in marine habitats.
Example – Sycon, Euplectelea

Animals living in water and show more body design differentiation. There is a cavity in the body and the body is made up of two layers of cells – one makes up cells on the outside of the body and the other makes the inner lining of the body. They show division of labour

Some of these species live in colonies are called corals, while others have a solitary like span are called hydra.
Example – Jellyfish, sea anemone

They have bilaterally symmetrical body that means the left and right halves of the body have the same design. There are three layers of cells from which differentiated tissues can be made and hence called as tripoblastic.

The body is flattened dorsiventrally that means from top to the bottom body is flat and hence called as flatworms. They are either free-living or parasitic.
Example – planarians, liver flukes, Tapeworm

They have bilaterally symmetrical and triplobastic structure, however the body is cylindrical rather than flattened. They have tissues but no real organs, although a sort of body cavity or a pseudocoelom is present. Bodies of these animals are long and threadlike and hence called as roundworms. Ends of the body are pointed.

They are familiar as parasitic worms causing diseases like worms causing elephantiasis or the worms in the intestines like roundworms.
Example – ascaris, wuchereria, Guineaworm

They have bilaterally symmetrical and triplobastic structure with a true body cavity. They show extensive organ differentiation which occurs in a segmental fashion, with the segments lined up one after the other from head to tail. Body of these animals appears to be made up of many ring-like segments, the animals are called annelida.

These animals found in a variety of habitats – fresh water, marine water as well as land.
Example – Leech, earthworm,Nereis

They have bilaterally symmetrical and segmented. They have open circulatory system, and so the blood does not flow in well defined blood vessels. The coelomic cavity is blood-filled. They have joined legs.
Example – butterfly, cockroach, housefly, mosquito

They have bilaterally symmetrical and little segmentation. The coelomic cavity is reduced and has little segmentation. They have open circulatory system and kidney like organs for excretion. They have foot for moving around. Bodies of these animals are soft and hence called as mollusca.
Example – chiton, octopus, slug, bivalve, cowrie, conch

Echinos means hedgehog and derma means skin. They are spiny skinned organism and exclusively free-living marine animals. They are triploblastic and have a coelomic cavity. They possess peculiar water driven tube system for moving around and have hard calcium carbonate structure that they use as a skeleton. Body of these animals are covered by calcareous spines and hence called as echinodermata.
Example – star fish, sea cucumber etc.

They have true vertebral column and internal skeleton for movement. They have a completely different distribution of muscle attachment points to be used for movement.

They are bilaterally symmetrical, triploblastic, coelomic and segmented, with complex differentiation of body tissues and organs. They are further classified as
  Pisces – fish
  Amphibia – Frog
  Reptilia – turtle
  Aves – All birds like crow, pigeon, sparrow etc
  Mammalia – All mammals like human

All vertebrates possess following common features

  • Have a notochord
  • Have a dorsal nerve cord
  • Are triploblastic
  • Have paired gill pouches
  • Are coelomate

1.  Pisces:
They are marine animals like fish. Their skin is covered with scales or plates. They obtain oxygen dissolved in water by using gills. The body is streamlined and a muscular tail is used for movement. They are cold blooded and their hearts have only two chambers and lay eggs.

Some of them have skeletons made up of cartilage like sharks and some with a skeleton made up of both bone and cartilage like tuna or rohu.

2.  Amphibia
  They differ from the fish in the lack of scales, in having mucus glands in the skin and a   three-chambered heart. Respiration is through either gills or lugs. They lay eggs and found   both in water and on land.
  Example – Frogs, toads, salamanders

3.  Reptilia
  These animals are cold-blooded, have scales and breathe through lungs. While most of them   have a three-chambered hear, crocodiles have four heart chambers. They lay eggs with tough   covering and do not need to lay their eggs in water.
  Example – Snakes, turtles, lizards and crocodiles

4.  Aves
  They are warm-blooded animals and have a four chambered heart. They lay eggs. There is an outside covering of feathers and two forelimbs are modified for flight. They breathe through   lungs.
  Example – Birds

5.  Mammalia
  They are warm-blooded animals with four-chambered hearts. They have mammary glands for   the production of milk to nourish their young. Their skin has hairs as well as sweat and oil   glands. They are familiar for producing young ones.

Invertebrates and Vertebrates
Living organisms show diversities in their structure, functions and behavior. Depending on their similarities and differences, organisms are classified into different classes or groups. All the living organisms are identified and categorized on the basis of their evolution.  Most life forms that we see today have arisen by an accumulation of changes body design that allows the organism possessing them to survive better.

Difference between invertebrates and vertebrates:

Invertebrates Vertebrates
Vertebral coloum is not developed Vertebral coloum is developed on dorsal side of the body
Specific organ craniumis absent Cranium is present in head region
Notochord persists throughout the life span Notochord is transformed into vertebral column
Ex – Earthworm and cockroach Ex – Frog and rat

Nomenclature of animals:
Carolus Linnaeus is the scientist who introduced the system of scientific naming or nomenclature. Scientific name is given to the organism for their uniqueness and to identify them anywhere in the world. The scientific name of an organism is the result of the process of classification which puts it along with the organisms it is most related to.

Certain conventions are followed while writing the scientific names:

  • The name of the genus begins with a capital letter
  • The name of the species begins with a small letter
  • When printed, the scientific name is given in italics
  • When written by hand, the genus name and the species name have to be underlined separately.

Self study:
Q-1: Match the following

Porifera Animal shows division of labor
Coelenterata Mesodermal cells
Echinodermata No body cavity
Arthropoda Cellular level of organism


Porifera Body of animal possess pores
Coelenterata Animal shows division of labor
Echinodermata Body of animal is covered by calcareous spines
Arthropoda Animals that contains jointed legs

Q-2: Name the worm-blooded animals with mammary gland for production of milk to nourish their young ones.

  1. Mammalia
  2. Aves
  3. Reptiles
  4. Pisces

Answer: Mammalia are the worm blooded animals with mammary gland for production of milk to nourish their young ones.

Q-3: Body of the animals made up of many ring-like segments is called ……………..

  1. Coelenterata
  2. Porifera
  3. Annelida
  4. Nemetoda

Answer: Body of the animals made up of many ring-like segments is called annelid. © 2024 | Contact us | Terms of Use | Privacy Policy | Yellow Sparks Network
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