Animal Kingdom, Biology tutorial

Introduction to Animal Kingdom:

Animal is either vertebrate or an Invertebrate. This classification of animals is on the basis of presence and absence of vertebral column, generally referred to as backbone or spine in extremely developed animals. Animals which have vertebral column are known as vertebrates. On the other hand, those animals, which don't possess vertebral column, are known as invertebrates. In vertebrates, the Characteristics structure, notochord, develop in the embryonic period and afterward, same in replaced by the series of vertebrate, hardening vertebral column. In Invertebrate animals, notochord never grows. Thus, these are very frequently also designated as non-chordates or achordates.

General Characteristics of Invertebrates:

Invertebrates animals abound in number vary significantly, approx 95% of identified and explained species of living species of animals are invertebrates. They differ in size; few are microscopiclike Protozoans, whereas others are extremely large, like some huge cephalopods. Their shape is uneven and they illustrate different types of symmetry but significant number is Asymmetrical as well. Apart from protozoa other invertebrate phyla illustrates multicellularity. They exhibit various grades of body-organization; Protozoans and poriferans show cellular grade of organism but coelenterates show starting of tissue grade organization that has turn out to be more prominent in higher invertebrates. They integument of invertebrates is easy. The gut may be completely absent, or partly formed or entirely formed. Though, if present, it is all the time dorsal in position. Similarly, if heart is present, it is for all time dorsal in position. Nerve cord is ventral in position and solid in organization. Circulatory system, if present in invertebrates, may be open kind, or closed kind or mixture of both.

Difference between Invertebrates and Vertebrates:


Higher Invertebrate



Appendages if present are more than pairs.

There are never more than 2 pairs of appendages.


May have non-living exoskeleton

There is always the endoskeleton, composed of living tissues such as cartilage and bones.


The Central nervous system controls solid ganglia connected by nerve bones to form a chain.

Central nervous system is in form of hallow thick-walled tube


The nerve cord lies ventrally to the digestive tract.

Neutral tube lies dorsally to digestive tract.


The respiratory organs usually develop from the ectoderm.

Respiratory organs make in relation to wall of pharynx and comprise of gills or lungs, but gill clefts are present in embryo of all vertebrates.


The circulatory system is usually not closed.

Circulatory system is the closed system with veins, arteries and capillaries.


Heart is always dorsal in position.

Heart is always ventral and anterior.


Respiratory pigment haemoglobin, if present, dissolved in plasma.

Haemoglobin is included in red blood corpuscles.


Blood flowing through arteries may pass freely into body cavity.

Blood circulates through the closed system of vessels-arteries, capillaries and veins.


True tail is not found. Anus is terminal and opens at posterior end of body.

The true tail that may be stated as post anal continuation of body axis may be present.


Skin comprises of only one layer.

Skin comprise of 2 distinct layers, the outer epidermis overlying thick dermis.


Eyes develop from skin and not from brain. Compound eyes are frequently present.

Eyes grow as outgrowths of brain compound eyes are never found.


Alimentary canal present or absent

Alimentary canal all the time present.


No gill slits.

Gill Slits are there at least in embryos.


Reproduction sexual or asexual.

Gill Slits are there at least in embryos.

Phylum Protozoa:

The term Protozoa refers to Unicellular or acellular animals of microscopic size. They form simplest of all groups in animals' kingdom. Name protozoa means "first animals" and derived from 2 Greek words, PROTOS, means first and zoon, meaning animal. They are looked on as most primitive form of life, appearing first in evolutionary history. Structurally the protozoan is one-called animal similar with one cell or METAZOAN but functionally it is the complete organisms, physiologically balanced and executes all necessary process of the animal, therefore protozoans are known as acellular or non-cellular organisms.

Distinctive Features of Phylum Protozoa:

  • Mode of life can be free-living or parasitic.
  • Presence of moisture in the environment is the necessary condition for the mode of life.
  • Locomotry organs are finger - such as Pseudopodia or whip-like Flagella or hair-like Cilia or absent. Meganucleus) like Paramecium.
  • Nutrition may be holozoic (animal-like), holophytic (Plant-like), Sapro-phylic or parasitic.
  • Respiration happens through general surface of body.
  • Excretion happens through general surface or through contractile vacuoles that also serve for Osmo-regution.
  • Reproduction occurs asexually by binary or multiple fission and budding, and sexually by conjugation of adults or female gametes.
  • Encystement generally happens to assist in dispersal and to pass unfavorable condition.

Categorization of Protozoan:

The categorization of Phylum Protozoa is based on locomotory Structure. Phylum Protozoa is separated into sub-phylia;

  • Plasmodrome; Members include Pseudopodia (false feet) or flagella or no locomotory structure like Amoeba, Euglenas.
  • Ciliophora: Members include cilia and more than one nucleus of which one is large (Meganucleus) like Paramecium.)

Amoeba Phylum - Protozoa:

  • Subphylum - Plasmodroma
  • Class - Rhizopods
  • Order - Lobosa
  • Genus - Amoeba


Structure of Amoeba:

Amoeba, the member of class Sarcodine is common example of simplest animal life and is generally universally studied as:

The most common species is Amoeba proteus. It estimates approx 0.25 to 0.60mm in size and is hard to see without the assistance of the microscope. Under microscope, it emerges as the minute slate - colored shining, irregular mass of the gelatin-like substance with study moving fine particles. It has irregular shape due to fact that protrusions of its own substance and created at its surface in various directions -Pseudopodia and they are continually changing in shape in achieve animal by protoplasm. It comprises of very- thing elastic external plasma membrane or plasmallema


Common Amoeba Proteus may be gathered from the variety of places where condition of water, temperature and organic food are favorable like debris from watering troughs, pools, drains, bottom of ponds, ditches, abandoned tanning pits and wherever there is plentiful aquatic vegetation.


Pseudopodia are related with ingestion of food and Locomotion. In Locomotion, it form one or more blunt finger-shaped procedure or pseudopodia that carry on to grow more and more by flow of protoplasm that is clearly withdrawn from somewhere else and, thus, if formation of Pseudopodium is mostly in one direction, amoeba shold change in position and it is in this manner that locomotion is affected.


This has particular reference to pseudopodia. If pseudopodium, extension, must come in contact with foreign body, like the grain of sand, it is retracted and new one is pushed out in changed direction. This signifies that made Protoplasm of amoeba has power to perceived nervous messages or stimuli over whole of its surface, as at whatever point pseudopodium is extended it will respond to this reaction.

Food and Feeding:

Aquatic environment of amoeba has small particles of different organic substances, appropriate for food. This comprises unicelluar plants, specific bacteria and diatoms, small filaments of algae, different protozoan species together with organic debris of several kinds. It is holozoic in nutrition, i.e., it ingests solid organic particle. This is with aid of pseudopodia.


There is no specialized organelle in amoeba for throwing out indigestible material. It leaves animal through temporary opening in ectoplasm at rear of animal. Plasmallema ruptures at point of contact with vacuole and feaces are egested or animal flows away. New plasmalemma is created at ruptured area to stop outflow of endoplasm.


Process whereby Carbondioxide leaving protoplasm is exchange for oxygen entering it, is called as Respiration. In amoeba this exchange is carried on essentially through general surface of body. Water in which amoeba lives should comprise dissolved oxygen in order that this diffusion may go on.

Osmo Regulation:

Osmo regulation refers to regulation of water content. Contractile vacuole is liable for the function. Contractile vacuole is clear space. It has the fluid less dense than surrounding protoplasm. At more or less regular intervals, it abruptly collapses, its walls having contracted, force out fluid contents that is known to have traces of urea and Carbon dioxide but generally water.


Reproduction is asexual and is by methods of:

  • Binary Fission
  • Sporulation
  • Encystment

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