Animal Kingdom I

Subject: Science

Overview

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On the basis of presence or absence of vertebral column, animal kingdom is divided into invertebrate and vertebrate.

Animal Kingdom

Animal Kingdom

Sub-Kingdom: Invertebrate

The animals which lack backbone or vertebral column are called invertebrates. The invertebrate animals are divided into nine phyla. All the unicellular organisms are included in protozoa while the multicellular organisms are in metazoan.

 

Differences between vertebrates and invertebrates:

Invertebrates Vertebrates
Backbone or vertebral column is absent. Backbone or vertebral column is present.
Brain is absent or in the form of paired ganglia above the pharynx. Brain is present.
They are cold-blooded. They are cold or warm blooded.
Skin consists of only a single layer. Skin consists of two layers: epidermis and dermis.
Red blood cells are mainly absent. Red blood cells are present.
Body shape is either irregular or regular. Body shape is mostly regular.
Asexual reproduction predominant. Sexual reproduction predominant.
 
The invertebrates are further divided into the following nine phyla,
 

Phylum: Protozoa

They have the following characteristics:

  1. The protozoans are small and microscopic animals.
  2. They are unicellular organisms.
  3. Excretion and respiration take place by general body surface or by contractile vacuole.
  4. They commonly move with the help of pseudopodia.
  5. Their body is naked or bounded by a pellicle.

Examples: amoeba, paramecium, euglena, plasmodium etc.

 

Phylum: Porifera

They are called sponges and have the following characteristics:

  1. They do not move from place to place. Thus, they are called sessile.
  2. Most of the sponges are marine except spongilla.
  3. Sponges have two types of openings in their body. Small pores are called ostia and large pores are called osculum.
  4. The presence of sponging fibre, calcium and silicon make the sponges body rigid and strong.
  5. Both asexual and sexual reproduction occurs in sponges.

Examples: sycon, spongilla, euspongia etc.

 

Phylum: Coelenterata

They have the following characteristics:

  1. The bodies of coelenterates are hollow and tubular cavity called coelentron.
  2. Mouth serves for both ingestion and egestion of food.
  3. Mouth is surrounded by tentacles which help in locomotion and capturing of prey.
  4. They are diploblastic animals.
  5. They reproduce by both asexual and sexual method.

Examples: hydra, obelia, jellyfish, corals etc.

 

Phylum: Platyhelminthes

These animals are known as flat worms and have the following characteristics:

  1. The flat worms are soft and flat either leaf-like or tape-like.
  2. Their head is provided with hooks and suckers.
  3. They have mouth but no anus in their alimentary canal.
  4. They are hermaphrodite as their body contains both male and female reproductive organ.
  5. They are usually parasites but few of them are free living.

Examples: liver fluke, tapeworm, etc.

 

Phylum: Aschelminthes or Nemathhelminthes

They are commonly called round worms and have following characteristics:

  1. The body of round worms is cylindrical and unsegmented.
  2. Their body is covered with thick cuticle.
  3. The digestive system is complete with mouth and anus.
  4. The circulatory and respiratory systems are absent.
  5. They reproduce by sexual method.

Examples: hookworm, earthworm, pinworm etc.

 

Differences between male and female ascaris:

Male Ascaris Female Ascaris
The male is smaller than female. The female is larger than male.
The tail of male is curved. The tail is straight and pointed.
In male, genital pore and anus open onto a common chamber, the cloca. In female, the genital pore and anus open separately.
Tail of male is provided with a pair of penial setae. Penial setae are absent.

 

Phylum: Annelida

They are known as segmented worms and have following characteristics:

  1. These animals are cylindrical, segmented and elongated.
  2. They have moist skin through which they respire.
  3. Locomotory organs are called setae or parapodia.
  4. Digestive system is complete, having mouth and anus.
  5. They are usually hermaphrodite while a few of them are unisexual.

Examples: earthworm, leech etc.

 
Things to remember
  • On the basis of presence or absence of vertebral column, the animal kingdom is divided into invertebrate and vertebrate.
  • The animals which lack backbone are called invertebrates.
  • All the unicellular organisms are included in protozoa while the multicellular organisms are in metazoan.
  • Phylum protozoa includes small, microscopic animals.
  • Poriferons are aquatic and most of them are marine.
  • Coelenterates are hollow and tubular and their cells are much more specialized than sponges.
  • The body of Platyhelminthes is flat, either leaf like or ribbon like.
  • Nemathhelminthes are free living animals in the sea, fresh water, or soil.

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